Early Career Conference in Trapped Ions (ECCTI) 2026, Oxford

6 Sept 2026, 12:00 → 11 Sept 2026, 17:00 Europe/London

Arjun Rao, Catherine Challoner (University of Oxford), Emma Vandrey (University of Oxford), Marion Mallweger (Stockholm University), Matthew Casey (University of Oxford)

Join us at ECCTI 2026 in Oxford, UK, from 6th Sept 2026 - 11th Sept 2026!

If you would like to attend the conference, please submit an abstract on the Call for Abstracts page. After confirmation that your abstract has been accepted, you will be allowed to register. In case of a room booking, the registration will be accepted after the payment has been received (this may take some days).

Due to the generous support of our Sponsors we are able to waive the conference fee. When registering for the conference, there will be an option to book accomodation as well. More details such as prices can be found here.

Conference information

ECCTI is intended to connect a broad community with very diverse scientific goals with common technical challenges.

We invite graduate students and early career researchers (within 5 years of completing a PhD) to share their cutting-edge work with a global audience. Dive into the physics research of today with a focus on:

• Atomic Clocks
• Quantum Information & Computation, Quantum Simulation, Quantum Technologies
• Antimatter Physics
• Precision & Molecular Spectroscopy
• Nuclear Physics

Why Attend? Engage in fruitful discussions shaping the future of physics. Connect with potential colleagues, broaden your perspectives, and partake in interactive sessions to develop skills essential for a successful career in research or industry. 

 🌈 We encourage applications from a diverse community. Part-time PhD students and those having been on career breaks are exempt from the 5-year post-PhD limit. Each application is assessed individually.

Monday 7 September

Welcome

10:05 Coffee Break

Nuclear Physics

1 Trapping and laser cooling of fast Sr+ beams: A stepping stone towards in-trap laser spectroscopy of short-lived isotopes

To better understand key nuclear properties, tremendous effort has been put into various theoretical models (eg. [1,2]), capable of reproducing experimental data with increasing accuracy. Benchmarking these models requires precise measurements of key nuclear observables, among which electromagnetic moments and charge radii play complementary roles. Laser Spectroscopy (LS) techniques allow one to measure all these quantities within a single experiment in an efficient and precise manner [3].

As an alternative to the well-established in-source and collinear LS methods, an offline beamline has been commissioned at KU Leuven to develop new spectroscopic methods to be implemented on trapped ions at Radioactive Ion Beam (RIB) facilities [4], complementing a pre-existing high-precision trap optimized for stable isotopes. This will substantially increase the laser-ion interaction time from a few microseconds to multiple seconds, ultimately limited only by the half-life of the radioactive ions. Via the excitation of weak transitions, such as radiofrequency transitions within a hyperfine manifold [5], electromagnetic moments beyond the electric quadrupole moment, like the magnetic octupole one, can be obtained. Therefore, another nuclear observable will be added as a benchmark for nuclear theory and provide information on the proton distribution inside the nucleus.

This contribution will give an overview of the project and present the latest results from our linear Paul trap, which includes the deceleration, trapping and laser cooling of Sr+ ions from 10 keV beam energy to below 10 mK temperature and the formation of Coulomb crystals. As an initial spectroscopic benchmark, the dipole-forbidden S1/2 → D5/2 transition was driven to quantify broadening mechanisms. Finally, the status of the ongoing installation of this setup at the IGISOL RIB facility [6] will be presented. The latter will enable both in-trap LS measurement of radioactive species and the preparation of ultra-cold ion bunches for Penning trap mass measurements [7].

References:
1. A. Ekstrom et al., Frontiers in Physics 11, 29094 (2023)
2. D. Bonatsos et al., Atoms 11(9), 117 (2023)
3. X. F. Yang et al., Progress in Particle and Nuclear Physics 129, 104005 (2023)
4. P. Imgram et al., Review of Scientific Instruments 96, 093302 (2025)
5. X. F. Yang et al., PRA 90, 052516 (2014)
6. I.D. Moore et al., Nuclear Instruments and Methods in Physics Research Section B 317, 208-213 (2013)
7. S. Sels et al., Physical Review Research 4, 033229 (2022)

Speaker: Stefanos Pelonis (Department of Physics and Astronomy, Instituut voor Kern-en Stralingsfysica, KU Leuven, 3001, Leuven, Belgium)

2 Towards ultra-high precision optical and radiofrequency spectroscopy of stable and radioactive Sr+

The nucleus is generally described using a number of observables, each providing a characteristic insight into nuclear properties. Two particularly interesting properties are the nuclear charge density distribution and nuclear multipole expansion. The charge density distribution is described by an expansion ($\delta\langle r^2 \rangle$, $\delta\langle r^4 \rangle$, $\delta\langle r^2 \rangle^2$...) and the nuclear multipole expansion is described similarly (magnetic dipole $\mu$, electric quadrupole $Q$, magnetic octupole $\Omega$...) [1]. Both distributions are successfully probed using Collinear Laser Spectroscopy (CLS) across the nuclear chart. However, the technique is limited in precision and can therefore only access the lowest order multipoles, $\delta\langle r^2 \rangle$, $\mu$ and $Q$.

Using ion traps, by operating in the Lamb-Dicke regime and exploiting long interaction times, allows us to improve the precision of the measurements by many orders of magnitude as compared to conventional methods used at Radioactive Ion Beam (RIB) facilities, gaining access to $\Omega$, $\delta\langle r^4 \rangle$ and $\delta\langle r^2 \rangle^2$. Despite extensive developments in ion trapping, an ion trap for high precision optical spectroscopy of short-lived radioactive isotopes has not yet been installed at an ISOL (Isotope Separator On-Line) facility [2]. This motivated the building of two ion trapping setups at KU Leuven, one aimed at high precision optical spectroscopy, the BICEPS (Bespoke Ion Cooling Experiment for Precision Spectroscopy) trap, and another focused on deceleration and trapping of radioactive ions [3]. Both traps are fully operational and actively performing measurements.

Using BICEPS, we will perform high precision Isotope Shift (IS) spectroscopy of stable bosonic Sr$^{+}$ isotopes, as well as radiofrequency spectroscopy, probing the hyperfine structure of ${}^{87}$Sr$^{+}$ to measure $\Omega$ [4]. Eventually, the IS will allow us to probe the higher order charge density moments and to put meaningful bounds on Beyond Standard Model (BSM) physics [5]. We have already performed first low-precision IS measurements on single ${}^{84}$Sr$^{+}$, ${}^{86}$Sr$^{+}$ and ${}^{88}$Sr$^{+}$ and currently performing Rabi oscillations between the two Zeeman levels of the ground state of ${}^{88}$Sr$^{+}$. This demonstrates our capacity to coherently manipulate state populations on single ions. Furthermore, in this contribution the ongoing developments of BICEPS regarding trap control and precision laser spectroscopy as well as prospects to measure nuclear observables with high precision on radioactive isotopes at an ISOL facility will be discussed.

[1] Reinhard, P. G., Nazarewicz, W., Garcia Ruiz, R. F., Phys. Rev. C, 101 (2020).

[2] Takamine, A. et al., Phys. Rev. Lett., 112, 162502 (2024).

[3] P. Imgram et al., Review of Scientific Instruments 96, 093302 (2025)

[4] Lewty, N., et al., Opt. Express, 20, 21379 (2012).

[5] Door, M., et al., Phys. Rev. Lett., 134, 063002 (2025).

Speaker: Robbe Van Duyse (KU Leuven)

Quantum Simulation

3 Non-paraxial effects on laser-qubit interactions

Optical tweezers offer new opportunities to control and manipulate trapped ions with applications in quantum information processing. We consider the light potentials induced on trapped ions by an optical tweezer beyond the paraxial approximation. Longitudinal field components in the beam center cause spatially-dependent Rabi frequencies and AC Stark shifts, leading to unexpected qubit-motion coupling [1]. We characterize single- and two-qubit gate infidelities due to this, and provide strategies to minimize adverse effects [2].
We further detail a novel method for driving a quantum logic gate which uses non-paraxial effects to excite the ion chain's vibrational modes [3]. The proposed gate may offer key benefits such as infrastructural simplification – the light only has to be supplied from one direction - and enhanced long-ranged interactions between the ion qubits. Finally, we detail a novel scheme to implement quadratic spin-phonon coupling using optical tweezers on trapped ions. With the addition of Mølmer-Sørenson-type interactions, we show the resulting system can be used to simulate a class of Bose-Hubbard models [4].

[1] R.J.C. Spreeuw. Physical Review Letters 125, 233201 (2020).
[2] Gallagher, L. P. H., et al. Physical Review Research 8, 013077 (2026).
[3] M. Mazzanti et al. Physical Review Research 5 (3), 033036 (2023).
[4] Gallagher, L. P. H., et al. Physical Review A 112, L020401 (2025).

Speaker: Louis Gallagher

4 Using Qudits for Quantum Simulation

Simulating non-adiabatic quantum dynamics, such as those governing photochemical processes in human vision or DNA resistance to UV, remains a major challenge [1]. Specifically, because these phenomena lie beyond the Born-Oppenheimer approximation, requiring both electrons and nuclei to be treated as an entangled quantum system, they are inherently hard to simulate classically. To describe these dynamics, we use the linear vibronic coupling model (LVCM), where $N$ electronic configurations couple to $M$ vibrational modes via vibronic couplings $\kappa_{mij}$:
\begin{equation}
H_{\text{mol}} = \sum_{i,j}^{N} \Delta_{ij} \psi_{i}^{\dagger} \psi_{j} + \sum_{m}^{M} \nu_{m} a_{m}^{\dagger} a_{m} + \sum_{m}^{M} \sum_{i,j}^{N} \kappa_{mij} \psi_{i}^{\dagger} \psi_{j} (a_{m}^{\dagger} + a_{m}).
\end{equation}
Previous simulations restricted this model to two electronic states ($N=2$) via single-qubit encodings. We overcome this bottleneck by employing qudits, directly expanding the simulation to $N=d$ configurations. Trapped ions provide an ideal mapping for this scaled architecture. The $d$-dimensional electronic space is encoded into discrete internal ion states, while the vibrational modes map naturally onto the continuous motion of a calcium-ion chain.

A key objective of this work is to assess how various algorithmic and physical error sources impact the simulation. First, since LVCM interaction terms are not natively available, we theoretically derive the necessary gate sequences for a qutrit ($d=3$) to implement short-time evolution operators, which are then combined using Trotterization. Second, we study how experimentally relevant noise sources, such as motional heating, amplitude damping, and dephasing, impact these simulated dynamics. Finally, we analyze the validity of the Lamb--Dicke approximation, quantifying the systematic errors that arise when approaching its breakdown regime. For our qutrit encoding, we aim to identify an optimal operating regime that balances these competing errors within the hardware's coherence limits.

Our work will provide concrete parameters for feasible simulations on the MILC trapped-ion platform and establish a pathway toward scaling to higher-dimensional qudits ($d>3$). Over the next five months leading up to the conference, I will extend these pulse constructions to larger qudit spaces, refine the error models, and explore noise mitigation strategies. By establishing these theoretical bounds, this work will dictate exactly which complex non-adiabatic chemical dynamics can be feasibly simulated on current trapped-ion hardware.

1. M. Kang et al., Seeking a quantum advantage with trapped-ion quantum simulations of condensed-phase chemical dynamics, Nat. Rev. Chem. 8 (2024), pp. 340–358.

2. J. Whitlow et al., Quantum simulation of conical intersections using trapped ions, Nat. Chem. 15 (2023), pp. 1509–1514.

3. C. H. Valahu et al., Direct observation of geometric-phase interference in dynamics around a conical intersection, Nat. Chem. 15 (2023), pp. 1503–1508.

4. T. Navickas et al., Experimental quantum simulation of chemical dynamics, arXiv:2409.04044 (2024)

Speakers: Irini Lindmar (ETH Zürich), Mr Raffaele Lanini (ETH Zürich)

5 Single-Setting Measurements for Characterizing Many-Body Quantum States

In quantum computations and simulations, it is important to have methods for measuring properties of interest of the quantum system. For small systems containing only a few qubits, the gold standard is to reconstruct these properties via quantum state tomography (QST). However, the number of distinct measurement settings required to obtain a tomographically complete dataset scales exponentially with the number of qubits. For intermediate-scale quantum simulators beyond only a few qubits, QST already becomes unfeasible. We therefore forsake the goal of reconstructing the entire quantum state and turn to methods that allow arbitrary properties of a quantum state's density matrix to be estimated directly.
One such method is the implementation of a symmetric informationally complete positive operator-valued measure (SIC-POVM), in which a single experimental setting provides access to an informationally complete measurement record.
I will present our latest experimental advances in implementing such a SIC-POVM-based measurement on our trapped-ion quantum simulator with 91 highly connected ion qubits arranged in a 2D crystal. Following Ref. [1], we implement the SIC-POVM by locally mapping the prepared qubit state onto multiple energy eigenstates of the $^{40}\mathrm{Ca}^{+}$ ion and detecting the POVM outcomes in a sequence of repeated exposures recorded in a single camera image, differentiating between four different brightness levels.
In contrast to more commonly used measurement schemes based on projection-valued measures, which require an additional layer of single-qubit addressing to apply random unitaries or rotate each qubit into the desired measurement basis, thereby adding experimental complexity and potentially errors, the method we use can be implemented entirely within a single experimental setting. It is independent of system size due to the use of global laser pulses acting on all ions in parallel. Because each shot of the SIC-POVM samples from an informationally complete distribution of the full quantum state, the method naturally combines with recent advances in randomized measurements and enables realtime estimation of arbitrary polynomial functions of the density matrix, with precision improving as more repetitions are accumulated.

[1] Stricker et al., PRX Quantum 3, 040310 (2022)

Speaker: Leo Walz (Universität Innsbruck)

12:30 Lunch

Quantum Simulation

6 Interaction-Induced Dynamics in Ultracold Atom–Ion Mixtures

We investigate quantum atom-ion scattering in the s-wave regime using a
hybrid apparatus comprising a single $^{138}$Ba$^{+}$ ion in a linear Paul trap and a $^{6}$Li Fermi gas. The atomic sample is prepared via sequential cooling in a magneto-optical trap (MOT) and a compressed MOT (cMOT) before confinement in a crossed optical dipole trap (xODT). Inelastic collision rates are manipulated via magnetically tunable Feshbach resonances. To overcome micromotion-induced energy limits in RF traps, we use radial displacement fields $E_{dc}$ to control the ion’s excess kinetic energy $\Delta E_{\text{ion}}$. This technique, calibrated via molecular dynamics (MD) simulations, allows for the systematic tuning of collision energies over four orders of magnitude—from the classical $E^{−3/4}$ scaling regime to below the s-wave limit $E_{s} = 8.8$ µK · $k_{B}$.
We present a characterization of the Feshbach spectrum between 240 G and
340 G with an average resonance density of 0.58(1) G$^{−1}$, utilizing fluorescence-based detection of ion survival probability $P_{\text{surv}}$. Technical emphasis is placed on the manipulation of the substructure of individual three-body resonances. We demonstrate that the resonance position, width, and amplitude are modulated by the external fields and the ion’s driven motion. These techniques enable high-speed interaction control, a prerequisite for future many-body quantum
simulations.

Speaker: Alexander Döring (Universität Freiburg)

Quantum Technologies

7 Fundamental building blocks for a trapped-ion quantum repeater link

The quantum repeater (QR) [1] is a fundamental building block for the realization of large, long-distance quantum networks. By dividing a transmission link into segments of entangled quantum memories and cells generating asynchronously entangled photons [2], it is possible to overcome the exponential loss of direct transmission.
We report on the implementation of a quantum repeater cell with free-space-coupled photons from two $^{40}$Ca$^+$ ions in the same Paul trap acting as memories. Ion-photon entanglement is generated asynchronously by controlled emission of single photons from the individually addressed ions into separate single-mode fibers. Photon-photon entanglement with 77.8(6)% average fidelity is then generated by applying a Mølmer–Sørensen gate and state projection of the ions.
The advantage of this protocol is highlighted by a 100-fold improvement of the photon pair probability compared to a synchronously operated QR cell, resulting in a single-attempt probability of $9.76(2)\cdot10^{-5}$ and a photon-pair detection rate of $11.34(2)$s$^{-1}$ [3].
A QR segment connects individual QR cells to form a quantum repeater link. We demonstrate the implementation of such a segment in the same setup with two $^{40}$Ca$^+$ quantum memories that are entangled by entanglement swapping of free-space-coupled single photons after generating ion-photon entanglement [4].
Entanglement of the two memories is verified by a parity measurement using two $\pi/2$ rotation pulses on the ions after photonic coincidence detection. To demonstrate the possible use for heterogeneous systems in which the second memory emits at a different wavelength, and to reduce attenuation for long-distance communication, the photons are converted to the telecom C band using polarization-preserving quantum frequency conversion [5] before their detection.
The parity oscillation shows a peak-to-peak value of 1.36(15), with a value larger than one being sufficient to prove entanglement [6]. This corresponds to a fidelity of better than 68(8)%. We produce entangled memories at a rate of 4.7 per day, which will be enhanced in the future by the use of an optical resonator.

[1] H.-J. Briegel et al., Phys. Rev. Lett. 81, 5932 (1998)
[2] P. van Loock et al., Adv. Quantum Technol., 3: 1900141 (2020)
[3] M. Bergerhoff et al., Phys. Rev. A 110, 032603 (2024)
[4] P. Baumgart, et. al. Optica Quantum 2.0 Conference and Exhibition, paper QTh4A.3 (2025)
[5] E. Arenskötter et al., npj Quantum Inf 9, 34 (2023).
[6] L. Slodicka et al., Phys. Rev. Lett. 110, 083603 (2013)

Speaker: Max Bergerhoff (Saarland University)

8 Scalable components for microwave-driven cryogenic trapped-ion quantum computing experiments

Surface electrode ion traps are a promising platform for building quantum computers. In our cryogenic experiments, we encode qubit states in a first-order magnetic field insensitive hyperfine transition. The qubit control is implemented with microwave conductors that are integrated into the chip, following the microwave near-field approach, which reduces the number of lasers required.
To scale up the number of qubits, we need to commission more advanced chips, develop methods to significantly increase the number of electrical signals required for dense ion storage and transport zones on future chips, and need to develop more integrated laser access.
In one experiment, we are commissioning an 8-qubit chip with a qubit interaction zone in between two storage registers. All-to-all connectivity will be implemented through swapping operations combined with linear transport between the storage zones. An upcoming junction chip for several more ions is also going to be installed in a second experiment later this year.
In a third experiment, we are exploring hybrid-integrated cryogenic control electronics, such as integrated microwave sources and DACs for multiplexed ion shuttling. Reducing the number of cables entering the cryostat will reduce the conductive heat load and enable more advanced chip architectures.
A scalable system will inevitably require a larger chip size with dedicated zones for cooling and detecting ions. To enhance the laser access for larger chip sizes, we are preparing to upgrade a fourth experiment to use integrated waveguides in trap chips and report on the progress made towards this.

Speaker: Sophie Najwa Al-Zaki (Leibniz Universität Hannover)

9 Ion trap surface investigation using Kelvin probe force microscopy

For applications of ion traps in quantum computing and metrology, understanding the origins of anomalous heating and dc stray fields is highly relevant. Anomalous heating and stray fields can both be linked to effects occurring on the ion trap surface e.g., adsorbate movement, fluctuating dipoles, two level fluctuators for anomalous heating and laser-induced charging, surface contaminations for stray fields[1], [2]. Despite numerous studies on different materials no definitive conclusion on root causes could be reached, yet. Some of the most recent studies focus on analyzing the elemental composition of ion trap surfaces using techniques such as Auger electron microscopy and X-ray photoelectron spectroscopy (XPS), aiming to improve the understanding of ion trap surfaces[3], [4].
In our research, we use a Kelvin probe force microscope (KPFM) to study ion trap surfaces. Unlike XPS, KPFM does not analyze the elemental composition of the surface, but rather the electrical potential. The KPFM technique is based on atomic force microscopy; therefore, a very fine tip is used to scan the sample surface. During this scan, the topography and surface potential are mapped simultaneously. The ion trap potential can be derived from the electrical potential the tip is measuring. However, due to the tip's small diameter of approximately 10 nm, a much higher lateral resolution can be achieved than with the ion itself.
Using this technique in ambient conditions, we demonstrate that the common assumption in ion trapping, that metals have an equipotential surface, is a drastic oversimplification. For both noble and non-noble metals, we found that surface potential divergences of 50–100 mV are common for chip trap surfaces. In certain cases, potential changes up to 0.5V were found. The main reasons for these changes in potential are grain boundaries and changes in grain structure.
In addition to these changes in untreated surfaces, we demonstrated that exposing aluminum to blue laser wavelengths alters the surface potential by up to 0.45 V (Illumination settings: Wavelength:405nm; Laser Power: 100µW; Laser diameter: 10µm; Illumination time: 5s) . We demonstrated that the change in potential is locally confined and stable over several days. Experiments are currently being conducted to show the correlation between these KPFM measurements and in-situ ion trap measurements

[1] S. X. Wang et.al „Laser-induced charging of microfabricated ion traps“,
doi: 10.1063/1.3662118.
[2] M. Brownnutt et.al, „Ion-trap measurements of electric-field noise near surfaces“, doi: 10.1103/RevModPhys.87.1419.
[3] M. Berlin-Udi et al., „Changes in electric field noise due to thermal transformation of a surface ion trap“, doi: 10.1103/PhysRevB.106.035409.
[4] J. A. Sedlacek et al. „Evidence for multiple mechanisms underlying surface electric-field noise in ion traps“, doi: 10.1103/PhysRevA.98.063430.

Speaker: Christian Flasch (Infineon Technologies Austria AG, Villach, Austria; Physikalisch-Technische Bundesanstalt, Braunschweig, Germany)

15:00 Coffee Break

Quantum Computing

10 Computational Capabilities and Compilation Strategies for Trapped-Ion Quantum Computers

Trapped-ion quantum computers mature to larger qubit numbers, but their computational capability is limited by architectural and control constraints. We present a framework for quantifying and optimizing the computational capabilities of trapped-ion processors. Using compiler techniques from classical computer science, we show how arbitrary quantum circuits can be mapped to hardware-efficient sequences of operations, optimized for metrics such as shuttling distance and gate overhead. The approach builds on and extends existing work on circuit compilation for trapped-ion quantum computers [1], and relates to analogous compiler frameworks developed for neutral atom systems [2]. It is demonstrated for both 1D and 2D [3] shuttling architectures, and extended toward logical qubit encodings to support fault-tolerant operations in future large-scale systems. In this context, we introduce a universal routing and scheduling algorithm for a shuttling-based trapped-ion quantum computer that efficiently orchestrates qubit register reconfiguration and gate execution, tailored to varying levels of ion-qubit connectivity.

---

References

[1] Kreppel, F., et al., Quantum circuit compiler for a shuttling-based trapped-ion quantum computer, Quantum 7, 1176 (2023).
[2] Schmid, L., Locher, D., Rispler, M., Blatt, S., Zeiher, J., Müller, M., Wille, R., Computational Capabilities and Compiler Development for Neutral Atom Quantum Processors - Connecting Tool Developers and Hardware Experts, Quantum Science and Technology (2024).
[3] Schoenberger et al., Shuttling for Trapped-Ion Quantum Computers with Embedded Processing Zones, Proc. IEEE QSW (2025).

---

This work is carried out in collaboration with the group of Prof. Robert Wille (Technical University of Munich) and neQxt GmbH.

Speaker: Jurek Eisinger (Johannes Gutenberg University Mainz)

11 Superconducting Ion Trap System for 87Sr+ Hyperfine Qubit

Large-scale trapped-ion quantum processors require highly integrated control architectures capable of supporting high-fidelity gate operations. An all-electronic control platform offers significant advantages in on-chip integration, scalability, and operational fidelity. Recently, a near-field gradient-based entangling method has demonstrated the highest two-qubit gate fidelity among all quantum computing platforms [1].
To date, the near-field gradient required for entangling operations is typically generated by alternating currents flowing through normal-metal trap electrodes. The maximum current that can be applied is constrained by Joule heating in the narrow trap electrodes and the associated power limits required to prevent chip damage. This limitation not only restricts the achievable gate speed but also presents a significant challenge for scaling to large systems, where tens to hundreds of traps may be integrated on a single chip, as the total power dissipation becomes substantial.
To address this challenge, we have demonstrated a full-superconducting surface ion-trap design incorporating a high-Q microwave resonator that generates sub-ampere oscillating currents with sub-milliwatt input power [2]. Furthermore, hyperfine splitting in trapped ions enables qubit encoding in the microwave regime, allowing compact on-chip resonator designs while maintaining long coherence times. Based on these considerations, the 87Sr+ ion is selected as the qubit platform.
In this work, we present the current progress in developing a cryogenic system for a superconducting ion trap based on 87Sr+ ions. This includes the design of a superconducting helical resonator, fabrication of the superconducting ion trap, and the implementation scheme for 87Sr+ ion operation.
[1] A. C. Hughes. et al. arXiv:2510.17286 [quant-ph] (2025)
[2] Y. Tsuchimoto, et al. EPJ Quantum Technol., 11 1 (2024) 56

Speaker: Qifeng Lao (Komaba Institute for Science (KIS), The University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan)

12 Distributed quantum error detection across a trapped-ion network

One approach towards a utility scale quantum computer uses smaller processors that are linked via a quantum network. In such systems, both computation and error correction must be performed across these nodes. Here, we demonstrate quantum error detection across a distributed trapped-ion network. Logical qubits are encoded in physical qubits that are spatially separated across two ion traps, $\sim 2~\mathrm{m}$ apart. Shared entanglement is used as a non-local resource to measure stabilisers between them.

Our platform consists of two mixed-species ion trap modules that are linked photonically, each containing $^{88}\mathrm{Sr}^+$ network qubits and $^{43}\mathrm{Ca}^+$ circuit qubits. Remote entanglement between network qubits is created by generating one photon from each ion and interfering them, with coincident detection heralding entanglement, achieving fidelities exceeding 96\% at a rate of $\sim 10~\mathrm{s}^{-1}$ [1]. Combined with mixed-species entangling gates, and classical feedforward, we have performed teleported gates between remote circuit qubits [2].

Building on this, we implement non-local stabiliser measurements using our shared Bell pair as an ancilla. Specifically, we encode logical information in the $X$-basis subspace of two remote circuit qubits and measure the $XX$ stabiliser with local entangling operations and measurements on the network qubits. We characterise the performance of a single round of this stabiliser measurement across a range of dephasing error rates. By conditioning on successful detection outcomes, we observe clear error suppression and an improved stabiliser value. Repeating this over multiple rounds progressively enhances the stabiliser expectation value, a key requirement for quantum error correction. Finally, we will extend the protocol to entangled logical states by preparing the remote circuit qubits in a Bell state, and then detecting and correcting both phase- and bit-flip errors on this state.

Our demonstration of non-local stabiliser measurements across a
quantum network establishes a key building block for scalable, fault-tolerant quantum computing in modular architectures.

[1] D. Main et al., arXiv:2506.14334.
[2] D. Main et al., Nature 638, 383–388 (2025).

Speaker: Ms Ellis Ainley (University of Oxford)

13 Scaling up trapped ion processors using high-speed and high-connectivity two-qubit gates

Conventional two-qubit gate mechanisms feature high connectivity between spatially-separated qubits, mediated by collective vibrations of ions within a single trap. However, controlling off-resonant excitation of spectator modes becomes increasingly challenging as the length of the chain increases, reducing gate speeds and fidelities. Modern architectures circumvent this challenge by separating ions into small chains connected via ion shuttling or photonic interconnects. However, these approaches introduce significant resource overheads, making them the primary bottlenecks when scaling trapped-ion processors.

An alternative pathway to increasing quantum logic rates in trapped-ion systems is to employ ‘fast gate’ protocols, where the ions are subject to sequences of spin-dependent kicks (SDKs) driven by broadband laser pulses. Previous studies suggest fast gates can enable MHz quantum logic rates in current trapped-ion processors without reduction of gate speed in scaled ion crystals, while also supporting more flexible trap geometries. However, while fast gates have been widely studied in the context of nearest-neighbour operations, their potential for enabling scalable, high-connectivity architectures remains an open question.

We present a theoretical study of fast all-to-all entangling gates in trapped-ion processors [1]. We explore how fast gate protocols operating in different regimes of the ion dynamics can be exploited to achieve high-fidelity, non-local entangling operations in scalable trapped-ion crystals. In particular, we identify a regime of phonon-mediated entanglement in which gates between arbitrary ion pairs can be performed in approximately 1.3-2 center-of-mass oscillation periods. We further assess the experimental feasibility of the proposed gate schemes, showing that the required SDK resources are independent of both chain length and qubit separation [2].

These results suggest that entangling gates based on impulsive spin-dependent excitation can overcome key scaling bottlenecks in trapped-ion platforms, and outline pathways toward combining fast operation, high connectivity, and modular scalability in future quantum processors.

[1] I. Savill-Brown, J. J. Hope, A. K. Ratcliffe, V. D. Vaidya, H. Liu, et al. High-Speed and High-Connectivity Two-Qubit Gates in Long Chains of Trapped Ions. 2025. arXiv: 2506.11385 [quant-ph].
[2] I. Savill-Brown, Z. Mehdi, A. K. Ratcliffe, V. D. Vaidya, H. Liu, et al. Error-Resilient Fast Entangling Gates for Scalable Ion-Trap Quantum Processors. 2025. arXiv: 2508.07593 [quant-ph].

Speaker: Isabelle Savill-Brown (The Australian National University)

Social

Tuesday 8 September

Lab Tours

Poster Session: Poster Session 1

12:30 Lunch

Molecular Spectroscopy

14 Precision spectroscopy and coherent control of single molecular nitrogen ions

In this work, we demonstrate the quantum control and precision spectroscopy of a clock transition in a single molecular nitrogen ion. We report the first observation of Rabi oscillations and spectra on a mid-infrared electric-quadrupole rovibrational transition in a molecular ion, thus establishing a robust platform for the coherent manipulation of high-fidelity molecular qubits and clock transitions.
Our experimental architecture utilizes a single calcium atomic ion co-trapped with the molecule in a linear Paul trap. State detection is achieved via a quantum-logic-inspired scheme based on optical lattice-induced coherent motional excitation, enabling high-fidelity, non-destructive identification of the molecular state [1]. Due to the extremely narrow linewidth of the transitions, we employ wide-range rapid adiabatic passage (RAP) scans for initial signal identification, followed by iterative RAP-based frequency narrowing to enable high-resolution Rabi spectroscopy [2].
The spectroscopic measurements are referenced to the Swiss primary frequency standard at the Swiss National Institute of Metrology (METAS) via a stabilized optical-fiber link enabling SI-traceability of measured frequencies [3]. Our results demonstrate a clear pathway toward the realization of molecular clocks, the study of state-resolved reaction dynamics, tests of fundamental physics, and the development of molecular qubits for quantum information processing.

[1] Sinhal, M., Meir, Z., Najafian, K., Hegi, G., & Willitsch, S. (2020). Quantum-nondemolition state detection and spectroscopy of single trapped molecules. Science, 367(6483), 1213-1218.
[2] Shlykov, A., Diouf, M. L., Karl, R., Roguski, M., Joshi, U. C., & Willitsch, S. (2026). Quantum-logic spectroscopy of forbidden vibrational transitions in single nitrogen molecular ions. arXiv preprint arXiv:2603.10553.
[3] Husmann, D., Bernier, L. G., Bertrand, M., Calonico, D., Chaloulos, K., Clausen, G., ... & Morel, J. (2021). SI-traceable frequency dissemination at 1572.06 nm in a stabilized fiber network with ring topology. Optics express, 29(16), 24592-24605.

Speaker: Nicolas Adrian Nuñez Barreto (University of Basel)

15 Quantum Logic Spectroscopy - What happens if the Raman lasers can access the dissociation continuum?

H$_2^+$ is the simplest molecular system, and its energy-level structure can now be calculated at the parts-per-trillion level[1]. Comparing experimental and theoretical transition frequencies enables the improvement of the value of fundamental constants, such as the proton-to-electron mass ratio $\frac{m_p}{m_e}$[2].

An increased sensitivity to $\frac{m_p}{m_e}$ can be obtained when measuring microwave transitions between weakly-bound levels located just below the H(1s) + H$^+$ dissociation threshold. These levels are comprised of spin-rotational states from the highest vibrational level of the electronic ground state $X^{+~^2}\Sigma_g^+$ and the lowest vibrational level of the first excited electronic state $A^+~^2\Sigma_u^+$[3]. Using fast ion beams, microwave transitions between these levels have been observed[4].

In an ongoing experiment, H$_2^+$ ions are selectively prepared in weakly-bound levels using a resonant multi-photon excitation of H$_2$ Rydberg states, followed by field ionization. The resulting ions will then be injected into an RF ion trap for precision measurements[5].

To avoid destructive detection and ion loss, Quantum-Logic Spectroscopy can be employed[6], as already demonstrated in the determination of the hyperfine structure interval of the H$_2^+$ $X^+$ vibrational ground state[7]. In such measurements, a stimulated Raman transition in the infrared is used, which overcomes the small Lamb-Dicke parameter, typical of long-wavelength microwave transitions.

We discuss whether stimulated Raman transitions remain feasible for the weakly-bound states, where the lasers can access the vibrational continuum, potentially resulting in loss of the molecules because of photodissociation.

AC polarizabilities of the molecular levels and Rabi frequencies for the stimulated Raman transitions are calculated using a Green’s function technique. This eliminates the necessity for an explicit sum-over-states approach and naturally includes the effect of the continuum. Implemented using both the Numerov method and Discrete Variable Representation, the effects of all other rotational, vibrational (bound & continuum), and electronic levels are taken into account systematically.
In addition to a specific calculation for H$_2^+$, we also provide a widely applicable model involving Morse potentials, which can be easily adapted to other molecules.

References:
[1] V. I. Korobov et al., Phys. Rev. Lett. 118, 233001 (2017).
[2] S. Alighanbari et al., Nature 644, 69–75 (2025).
[3] R. Moss, Molecular Physics 80, 1541–1554 (1993).
[4] A. Carrington et al., Faraday Trans. 89, 603 (1993).
[5] D. Y. Knapp et al., 10.48550/arXiv.2602.15668 (2026).
[6] P. O. Schmidt, edited by D. Bruß et al., 799–826 (2016).
[7] D. Holzapfel et al., Phys. Rev. X 15, 031009 (2025).

Speaker: Srishti Sharma (Vrije Universiteit Amsterdam)

16 Infrared absorption spectroscopy of a single trapped polyatomic molecular ion

Quantum logic spectroscopy (QLS) has been established as a versatile technique for high-precision spectroscopic studies of diatomic molecular ions co-trapped with atomic ions in an ion trap, contributing to fundamental physics research and quantum information applications [1-6]. However, extending this protocol to larger polyatomic molecular species is challenging due to their more complex internal structure and has not yet been demonstrated experimentally. Furthermore, QLS is not directly applicable to studies that use broadband ultra-short laser pulses to investigate fast molecular processes such as intramolecular vibrational redistribution, which plays an important role in chemical and biological processes. Using an adapted version of quantum logic methods, we investigate polyatomic molecular ions by probing their photon-absorption signal. This is achieved by preparing the shared motional mode of the trapped molecular and atomic ions in a non-classical state that is sensitive to the momentum recoil associated with the absorption of a single photon [7]. We demonstrate this scheme by measuring the infrared absorption spectrum corresponding to the O–H stretch mode of a CaOH⁺ ion co-trapped with a Ca⁺ ion using broadband femtosecond laser pulses [8]. The measured spectrum shows good agreement with ab initio theoretical predictions for the transition frequency and oscillator strength. This suggests that the recoil detection method has potential applications in studying more complex polyatomic molecular ions at the single-particle level, such as in the initial identification of transitions, as well as in pump-probe experiments using femtosecond laser pulses that facilitate the investigation of ultrafast intramolecular dynamics [9]. Furthermore, improvements in the signal-to-noise ratio could enable single-shot readout using this technique, combined with spectral shaping this would allow for measurement-based rotational state preparation in polyatomic molecules.

[1] P. O. Schmidt et al., Science 309(5735),749-752 (2005).
[2] F. Wolf et al., Nature 530(7591), 457–460 (2016).
[3] C. W. Chou et al., Nature 545(7653), 203–207 (2017).
[4] M. Sinhal et al., Science 367(6483), 1213–1218 (2020).
[5] D. Holzapfel et al., arXiv:2409.06495 (2024).
[6] L. Qi et al., arXiv:2411.07137 (2024).
[7] C. Hempel et al., Nature Photonics 7, 630–633 (2013)
[8] Z. Wu et al., arXiv:2511.19687 (2025)
[9] P. Schindler, New J. Phys. 21(8), 083025 (2019).

Speaker: Tim Duka (Universität Innsbruck)

17 Novel Background-Free, Agent-Driven, Ion-Trap Action Spectrometer for Radioactive Molecular Ions

Radioactive molecules provide an incredible $10^{12}$-fold boost in precision for measuring parity violation in the nuclear weak force [1]. Realizing this potential requires accurate rotational spectroscopy to locate, assign, and control the relevant quantum states. Moreover, the rotational transitions of heavy, short-lived molecules lie in the microwave-to-radio domain, providing a powerful, largely untapped tool for radio astronomy to nucleosynthesis production pathways in space [2]. However, spectroscopic data on such radioactive molecules remain scarce due to low production rates, short lifetimes, and spectral complexity.

To explore these exotic species, we developed a novel ion-trap-based action spectrometer with single-ion sensitivity. The method integrates three techniques: Multi-Reflection Time-of-Flight (MRTOF) ion trap filtering, multi-step photon dissociation for resonance identification, and MRTOF enhancement of spatial resolution of constituent ions with single-ion detection – all within milliseconds. Our first spectroscopic results on SiO+ will be presented, along with our ongoing efforts to automate the setup using an agent-based digital twin.

[1] Karthein et al. Phys. Rev. Lett. 133, 033003 (2024)
[2] T. Kaminski et al., A&A 644, A59 (2020)

Speaker: Nicholas Schnoor

15:00 Coffee Break

Quantum Technologies

18 Conformal mapping for computationally efficient ion trap designs

Solving the electrostatic problems governing the potentials in ion traps is typically performed using numerical finite element methods. However, these simulations are slow due to the large number of mesh points needed to accurately approximate the potential. It has been recognised that translationally invariant [1] and axisymmetric [2] geometries can be solved analytically using the conformal mapping approach.
The solutions to Laplace's equation expressed in the complex plane are harmonic functions. Conformal maps are holomorphic functions which conserve this property. They can therefore be used to transform a solution from a simple geometry, such as a circle, to a more complicated geometry, such as an open polygon.
Historically, conformal maps have been used to calculate laminar airflow around a Joukowsky foil by transforming the solution obtained for a cylinder. Here, we employ the Schwarz-Christoffel transformation to calculate the electric potential and pseudopotential produced by arbitrary electrode configurations, to find optimal ion trap geometries with different boundary constraints.

[1] J. H. Wesenberg, PRA, 78, 063410 (2008).
[2] A. Valette and P. Indelicato, PRST, 13, 114001 (2010).

Speaker: Peter Drmota (University of Oxford)

19 A Cryogenic Surface Trap with Rydberg Ions

Trapped Rydberg ions are a unique platform for quantum information processing, metrology and simulations [1,2] as they combine the exceptional control over trapped ions with the tunable, long-range interactions of Rydberg states. Rydberg ions have been used to demonstrate sub-microsecond entangling gates [3] but one of the biggest challenges while working with Rydberg ions is double ionisation due to blackbody radiation since Rydberg states are close to the ionisation threshold. The operation of the system in a cryogenic environment would reduce this effect significantly and here we present such an experimental system. The setup hosts a surface ion trap, with separate trapping and experimental zones. The first measurements with the surface trap are presented with the goal of showcasing Rydberg excitations on such a system. The large polarisability of Rydberg ions makes them highly sensitive to surrounding electric fields and can be utilised as a precise probe for sensing microwave fields around the chip.
[1] M. Müller, et al., NJP, 10, 093009 (2008).
[2] F. Schmidt-Kaler, et al., NJP, 13, 075014 (2011).
[3] C. Zhang, et. al., Nature 580, 345 (2020)

Speaker: Vinay Shankar (Stockholm University)

20 Quantum characterization and control of single molecules

The QCosmo team studies quantum states and dynamics in trapped polyatomic molecular ions with quantum logic spectroscopy (QLS). This method maps molecular transitions to a co-trapped atomic logic ion via a shared motional mode, enabling robust and efficient state readout. We focus on novel spectroscopy techniques, rovibronic state preparation and control, and the possibilities and limitations of applying quantum information processing techniques such as quantum error correction to molecular ions [B. Furey et al. Quantum 8, 1578 (2024)]. We have measured the photodissociation spectra of CaOH$^+$ [Z. Wu et al. J. Chem. Phys. 161, 044304 (2024), and more recently the infrared vibrational transition frequency in the OH stretch mode of a single trapped CaOH$^+$ molecular ion using cat state recoil spectroscopy [Z. Wu et al., arXiv:2511.19687[quant-ph] (2025)]. This method uses non-classical spin-motion-entangled cat states to amplify the detection of the recoil of a single absorbed photon via an accumulated geometric phase. We are also developing Raman QLS to enable molecular hyperfine and rotational spectroscopy and control. Ongoing work includes planning and development of a cryogenic experiment with a segmented ion trap. The segmented design enables potential splitting, allowing the realization of specific Coulomb-crystal configurations of logic and spectroscopy ions. Additionally, it facilitates shuttling operations, such that selected ions are positioned in tightly focused laser beams to perform logic operations. The cryogenic environment suppresses quantum jumps from thermal radiation and background gas collisions, thus extending ion storage and coherence times. Also under development is an ion-injection system, which introduces molecular ions into the ion trap from an external source. It comprises a quadrupole mass filter and a quadrupole deflector, enabling a highly species-selective injection as well as flexible adaptation to different molecular species. The trap dynamics can be synchronized with the molecular injection by monitoring the ion yield using a time-of-flight mass spectrometer.

Speaker: Max Koppelstätter (University of Innsbruck)

21 Towards Cavity QED with Trapped Barium Ions

Scalability remains one of the central challenges to achieve fault-tolerant quantum computation in trapped-ion systems. A modular approach, where multiple ion trap modules are interconnected using optical photons [1] is a promising route to tackle this endeavor. In this context, efficient coupling of ions to well-defined optical modes is essential for achieving the remote-entanglement rates required between modules. Cavity QED in the strong coupling regime [2,3], with applications such as efficient single photon sources [4], nodes for quantum communication [5], and non-linear optics at the quantum level [6], enables fast ion-photon entanglement generation with applications in quantum computing and networks. We report our plans and progress towards implementing such a system with barium ions.

Small mode volumes that are required for strong coupling between the ion and cavity can be obtained using fiber-based microcavities [7,8]. We discuss progress and challenges towards integrating microcavities in an ion trap for coupling to barium ion’s strong S-P transition at 493 nm, with the long-term goal of using ion-cavity modules as nodes of a quantum network or qubits of a quantum computer that can be entangled by using photonic flying qubits. Cavities operating at short wavelengths have been hampered by degradation in vacuum [9]. We present results showing stable cavity operation at 493 nm in vacuum at low circulating powers [10].

Further, we discuss a number of planned experiments, including fast generation of atom-photon entanglement, fast cavity-assisted state readout, and state readout in the dispersive regime. Additionally, we present our monolithic ion trap platform fabricated via selective laser-induced etching (SLE) with integrated fiber-based Fabry-Perot cavity (FFPC). Together, these represent the crucial step toward a cavity QED system with barium ions, contributing to the broader effort of building modular trapped-ion quantum computers.

Acknowledgements
This work was supported by JST Moonshot R&D Grant Number JPMJMS2063 and MEXT Quantum Lead Flagship Program (MEXT Q-LEAP) Grant Number 20181503.

References

1. C. Monroe, et al., Phys. Rev. A 89, 022317 (2014).
2. H. J. Kimble, Phys. Scripta 1998, 127 (1998).
3. H. Takahashi, et al., Phys. Rev. Lett., 124.1, 013602 (2020).
4. M. Keller, et al., Nature 431, 1075–1078 (2004).
5. H. J. Kimble, Nature 453, 1023–1030 (2008).
6. D. E. Chang, et al., Nat. Photonics 8,403, 685–694 (2014).
7. E. Kassa, et al. Phys. Rev. Applied 23, 024038 (2025).
8. S. Gao, et al. Opt. Express 33, 39009-39022 (2025)
9. T. G. Ballance, et al.,” Phys. Rev. A 95, 033812 (2017).
10. D. Das, et al., arXiv:2603.17638 (2026).

Speaker: SAVELII DUDOLADOV (Okinawa Institute of Science and Technology)

Lab Tours

Wednesday 9 September

Lab Tours

Poster Session: Poster Session 2

12:30 Lunch

Clocks and Precision Spectroscopy

22 Towards a network of 43Ca+ optical clocks for entanglement-enhanced metrology

Over the past few decades, advancements in optical atomic clocks have enabled measurements of time and frequency with unprecedented stability and systematic uncertainty [1,2]. Precision frequency comparisons between macroscopically separated clocks have applications in geodesy [3], probing variations in fundamental constants, and in dark matter searches [4]. Frequency comparisons between independent clock systems are limited by the standard quantum limit (SQL). In contrast, a set of N entangled atomic clocks can achieve a $\sqrt{N}$ stability improvement to surpass the SQL and approach the Heisenberg limit - the ultimate precision possible in quantum theory.

We previously demonstrated this enhancement in a network of two \ion{Sr}{88} clocks [5] on the 674 nm $5S_{1/2} \leftrightarrow 4D_{5/2}$ quadrupole transition using Ramsey spectroscopy, whose stability was mainly limited by the short probe duration of 20~ms due to magnetic field fluctuations. We are now setting up the next generation of the experiment wherein we map the remote Sr-Sr entanglement onto two $^{43}$Ca$^+$ ions. The 729 nm $^{43}$Ca$^+$ $\vert 4S_{1/2}, F=4, m_F=4 \rangle \leftrightarrow \vert 3D_{5/2}, F=4, m_F=3 \rangle$ optical clock transition is field-insensitive at 4.96 G, enabling probe durations at the excited state lifetime limit of $\sim$ 1 s (comparable to the start-of-the-art clocks [1]) and thus improve our stability.

We will present progress towards these clock experiments, including the setup of a 729 nm laser system locked to a high finesse cavity, as well as fibre noise cancellation on a 20 m fibre. We will further present some theoretical work on quantum metrology with Dicke states in the presence of spontaneous decay in larger networks of clocks.

[1] M. C. Marshall et al., Phys. Rev. Lett. 135, 033201 (2025).
[2] E. Oelker et al., Nature Photonics 13, 714–719 (2019).
[3] T. E. Mehlstaubler et al., Reports on Progress in Physics 81, 064401 (2018).
[4] M. S. Safronova et al., Rev. Mod. Phys. 90, 025008 (2018).
[5] B. C. Nichol et al., Nature 609, 689–694 (2022)

Speaker: Ayush Agrawal (Department of Physics, University of Oxford)

23 Sensing thermal motion of single ions with structured light.

We present results showing that using LG beams allows sensing temperature in the direction perpendicular to the propagation of the beam and with increased sensitivity with respect to plane waves. We use two counterrotating and copropagating vortex laser beams, which isolates the azimuthal gradients of the fields, eliminating longitudinal and curvature effects. By performing Coherent Population Trapping spectroscopy with this configuration we are able to measure the thermal motion of the ion in the direction transversal to the propagation of the beam. Furthermore, by having tightly focused beams we can perform this experiments near the center of the vortex, achieving sensitivity beyond the plane wave Doppler Shift

Speaker: Muriel Bonetto (Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física, Buenos Aires, Argentina)

24 Three Body Quantum Scattering in a Hybrid Atom-Ion System

We investigate quantum atom-ion scattering in the s-wave regime using a hybrid system comprising a single ${}^{138}\text{Ba}^{+}$ ion trapped in a linear Paul trap and a near-degenerate ${}^6\text{Li}$ Fermi gas confined in a crossed optical dipole trap. The ion is positioned within the Fermi gas and will undergo collisions. Inelastic collisions are directly related to formation of molecular states. The rates of inelastic collision can be tuned via magnetic Feshbach resonances using external fields, allowing for the enhancement or suppression of molecular formation channels. The existence of those channels depend on electronic states. To date, we have characterised both two-body (atom-ion) and three-body (atom-atom-ion) processes. While Feshbach resonances are well-established in neutral atom experiments, achieving the ultracold regime in RF traps remains challenging due to micromotion, which limits the minimum achievable collision energy.
Building on our previous characterisation of resonances’ position, width, and asymmetry across parameter space (collisional energy, magnetic field, and atomic spin polarization), we present an ongoing study focused on manipulating the substructure of single three-body Feshbach resonances. We demonstrate that this substructure is modulated by the external fields and the ion motion. These investigations aim to refine the theoretical understanding of few-body dynamics in atom-ion systems and establish the precise control necessary for future many-body quantum simulations.

Speaker: Patrick Mullan (Albert-Ludwigs-Universität Freiburg)

25 Measurements of the bound-electron $g$ factor in highly charged ions: testing fundamental physics

The $g$ factor of the bound electron in few-electron highly charged ions is a highly sensitive probe for new physics and its measurement allows to test the predictions of quantum electrodynamics (QED) in the extremely strong electric field of the nucleus. Studying these simple atomic systems allows to examine bound-state (BS-) QED and even nuclear effects to high accuracy. ALPHATRAP [1] is a cryogenic Penning-trap apparatus for high-precision $g$-factor measurements. By confining single ions in ultra-stable electromagnetic fields, the $g$-factor can be determined at the sub-ppb level [2].
Here, I will present the results of our recent g-factor measurements at ALPHATRAP as well as the future plans on an even more precise measurement on $^{12}$C$^{5+}$ and $^{14}$C$^{5+}$.

[1] S. Sturm, \textit{et al}. \textit{Eur. Phys. J. Spec. Top.} \textbf{227}, 1425-1491 (2019).
[2] J. Morgner, \textit{et al}. \textit{Nature} \textbf{622}, 53–57 (2023).

Speaker: Max Anton Gramberg (Max Planck Institute for Nuclear Physics (DE))

15:00 Coffee Break

Quantum Computing

26 Implementing and Characterising Error Mitigation by Virtual Distillation under Structured Noise

Error mitigation is a key tool for improving the performance of near-term quantum devices, but its efficacy depends strongly on the structure of the underlying noise [1]. In realistic systems, errors can exhibit temporal and spatial correlations, which determine which suppression strategies are effective. Virtual distillation (VD) is a promising approach, where exponential error suppression in the estimation of observable expectation values is achieved by increasing the number of state copies [2,3,4]. Like many mitigation techniques, however, it relies on the assumption that noise acts independently across copies.

Here, we combine error mitigation with a direct probe of this assumption. We demonstrate VD for the first time on a trapped-ion platform and introduce a scheme based on randomised benchmarking using parallel (“k-copy”) sequences that isolates correlated error components with minimal experimental overhead. Applying this method before and after VD allows us to study the effect of correlated errors on its performance. Together, these results provide a scalable route to implementing, diagnosing, and validating error mitigation in the presence of structured noise.

[1] Z. Cai, et al., Rev. Mod. Phys. 95, 045005 (2023).
[2] B. Koczor, Phys. Rev. X 11, 031057 (2021).
[3] W. J. Huggins, et al., Phys. Rev. X 11, 041036 (2021).
[4] T. Araki, J. F. Goodwin, and B. Koczor, Phys. Rev. A 112, 042619 (2025).

Speaker: Iver Romvig Øvergaard (University of Oxford)

27 Generation of Two-Photon Entanglement Using a Single Ion--Cavity System

Control over the internal states of trapped ions makes them the ideal system to generate single
and two-photon states. Coupling a single ion to an optical cavity enables efficient emission of single
photons into a single spatial mode and grants control over their temporal shape, phase and frequency.
Using the long coherence time of the ion’s internal states and employing a scheme to protect the
coherence of the ion-cavity interaction, we demonstrate the generation of a two-photon entangled
state with full control over the phase. Initially, ion-photon entanglement is generated. A second
photon is subsequently generated, mapping the ion’s state onto the second photon. By adjusting
the drive field the phase of the entangled state can be fully controlled. We implement this scheme
in the most resource efficient way by utilizing a single 40Ca$^+$ ion coupled to an optical cavity and
demonstrate the generation of a two-photon entangled stated with full phase control with a fidelity
of up to 82\%.

Speaker: Adrien Amour (University of Sussex)

28 Observation of Cooperative Scattering Light in Trapped-Ion Crystals

Understanding the collective interaction of light with quantum emitters is of paramount importance in quantum optics and a wide range of applications. Trapped-ion systems provide an ideal platform for studying light–matter interaction at the level of a few atomic scatterers, offering precise control over both electronic and motional degrees of freedom, and enabling access to a regime where emitters can be individually controlled yet collectively probed.

We experimentally demonstrate control over the photon statistics of light emitted by several mutually independent quantum scatterers - trapper ions using interference. In particular, we observe a transition from sub-Poissonian to super-Poissonian statistics for constructive and destructive interference of the elastically scattered component of resonance fluorescence, respectively. We show that this effect can be exploited in the mesoscopic regime to achieve deviations from the thermodynamic limit of photon statistics, highlighting the persistent role of coherent scattering. The interference between coherent scattering and spontaneous emission leads to spatial variations in both intensity and two-photon correlations, $g^{(2)}(\tau=0)$, demonstrated for ion chains with up to 18 ions.

To further enhance control over trapped ion–light interactions and to enable the observation of subtle cooperative phenomena~\cite{Item2, Item3}, we implement several crucial methods to increase the coherent fraction of scattered light. This is achieved by implementing electromagnetically induced transparency cooling of linear strings of $^{40}$Ca$^+$ ions, combined with a fast pulsed excitation sequence that optimizes coherent scattering on a selected dipolar transition within the S–P level transition manifolds. With these improvements, we reach unprecedentedly high coherent fractions in the scattered light. For example, the interference visibility for a four-ion string reaches $97.4\pm 0.9$ %, approaching the limit set by ground-state position uncertainty.

This enhanced control enables the observation of the onset of cooperative effects in a well-controlled and addressable system of laser-cooled ion strings. In particular, we resolve significant peak-to-peak modulations of the scattering rate arising from dipole–dipole interactions between two ions in a steady-state, with amplitude of up to $\sim$2 % and investigate its scaling with the number of ions in the crystal.

Our results mark a new milestone in optical scattering from ion crystals, bridging the regime from interference-dominated photon statistics to one where cooperative emission effects become observable. This establishes trapped-ion crystals as a platform for exploring cooperative quantum optical phenomena in fully controlled and addressable systems, and for engineering novel quantum light sources based on mesoscopic many-body light–matter interactions in free space.

Speaker: Kratveer SINGH (Palacky University Olomouc)

29 Practical quantum error correction on maximally modular networked architectures

Scaling quantum devices while preserving coherence remains a central challenge for practical quantum computation. Quantum error correction (QEC) addresses this, but its implementation depends critically on hardware constraints. By the threshold theorem, errors can be suppressed arbitrarily by increasing the number of physical qubits if physical error rates fall below a code-dependent threshold, motivating architectures that combine scalability with high-fidelity qubits.

Trapped ions are a promising platform for QEC due to their high fidelities and connectivity, both advantageous for codes encoding a high number of logical qubits per physical qubits [1, 2]. Decoding speeds are also unlikely to be limiting due to the relatively slow gate speeds. The challenge is then to scale the architecture without degrading its appealing properties.

Traditional approaches scale trapped-ion systems either by extending ion chains or by shuttling ions between zones. Both define a single quantum processing unit (QPU) and face limitations at large scales: long chains suffer from overly crowded motional mode frequencies, while shuttling introduces overhead from transport and cooling. More broadly, scaling a single QPU appears challenging across qubit platforms.

Modular architectures offer a complementary approach, where multiple moderate-sized QPUs connected via entanglement enable universal quantum computation. This shifts the challenge from scaling individual QPUs to reliably generating inter-module entanglement, which has been demonstrated in trapped ions using photonic links [3, 4].

In this work, we study a “maximally modular” architecture where each QPU contains a minimal number of (around 2–5) ions [5, 6]. This keeps local operations fast and reliable, but makes probabilistic, noisy entanglement generation the main bottleneck. Its stochastic nature complicates QEC scheduling, as asynchronously generated entanglement must be coordinated to minimise redundancy and errors.

We develop scheduling strategies across multiple layers, including parallelised parity checks, cutoff policies for aborting delayed operations, and synchronised entanglement attempts. We numerically simulate the performance of our implementation using a realistic error model based on modular trapped-ion devices. Our analysis provides a practical framework for implementing distributed QEC in trapped-ions and beyond.
[1] N. P. Breuckmann et al., Quantum low-density parity-check codes, PRX Quantum 2, 040101 (2021).
[2] S. Bravyi et al., High-threshold and low-overhead fault-tolerant quantum memory, Nature 627, 778 (2024).
[3] L. J. Stephenson et al., High-rate, high-fidelity entanglement of qubits across an elementary quantum network, Phys. Rev. Lett. 124, 110501 (2020).
[4] D. Main et al., Distributed quantum computing across an optical network link, Nature 638, 383 (2025).
[5] N. H. Nickerson et al., Topological quantum computing with a very noisy network and local error rates approaching one percent, Nature Communications 4, 1756 (2013).
[6] N. H. Nickerson et al., Freely scalable quantum technologies using cells of 5-to-50 qubits with very lossy and noisy photonic links, Phys. Rev. X 4, 041041 (2014).

Speaker: Tenzan Araki (University of Oxford)

Thursday 10 September

Quantum Computing

30 Microwave-driven same-species sympathetic cooling

Trapped ions are a promising hardware platform for quantum computing as they unite properties such as long coherence times, high gate fidelities, low state preparation and measurement errors, and networking capabilities. While running algorithms composed of long gate sequences on trapped-ion quantum computers, it is essential to cool the ions' motional modes in order to minimise errors caused by motional heating. This can be achieved by sympathetically cooling the logic ion with an ion of a different species, such that the laser beams required for cooling one ion do not affect the information stored in the other. However, this approach significantly increases the hardware complexity, and the difference in mass between the ion species leads to a suboptimal cooling efficiency.

Using microwave-driven sideband cooling in combination with a narrow-linewidth quadrupole laser at 729 nm, we demonstrate sympathetic cooling with two ions of the same species to an average phonon number of $\overline n = 0.09(3)$. Due to the large hyperfine splitting of the $^{43}$Ca$^{+}$ ground-state manifold at 28.8~T, the information stored in the logic ion is well-isolated from the cooling process and the introduced error of $9(1)\times10^{-4}$ per cooling cycle does not limit algorithm performance.

In addition to reducing hardware complexity and increasing cooling efficiency, same-species sympathetic cooling offers the benefit that, between cooling cycles, the coolant ions could be repurposed as ancilla qubits for error correction schemes.

Speaker: Emma Vandrey (University of Oxford)

31 Non-destructive parity measurement of a motional cat state

Quantized motional states of trapped ions are a quantum degree of freedom that is emerging as a platform for applications such as quantum computing and quantum simulation that involve bosonic degrees of freedom. One important tool, useful for example in quantum error correction, is parity measurement. Non-destructive measurements of the parity of a motional state enable mid-circuit projections into eigenstates of parity and can be used for example in bosonic stabilizer error correction schemes. However, ion internal state measurements typically rely on conditional fluorescence of an ion, “bright” or “dark”. The state of a motional mode will generally not be preserved after “bright” detection due to motional heating when the ion experiences thousands of photon recoils.

To preserve motional information upon measurement, we engineer the motional modes of a multi-species ion chain and entangle the internal state of an ion with a motional state of a mode in which this ion does not participate. This enables protection of the motional state from decoherence due to photon recoils when the ion fluoresces. We aim to demonstrate non-destructive parity measurements and apply them to create and characterize motional “Schrödinger’s cat” states in a mixed-species ion crystal of 9Be+-25Mg+-9Be+. We entangle motional states with two internal states of the Mg+ ion using a parity operation. This parity operation is implemented with a simple ion trapping tool, a Raman carrier pulse, making use of its motional dependence due to a finite Lamb-Dicke parameter. The motional states are then swapped from the motional mode on which the entanglement was performed to a “protected” motional mode, in which the Mg+ ion does not participate, by applying oscillating fields to the trap electrodes that coherently couple the two modes. Fluorescence detection on the Mg+ ion projects it to a particular internal and motional state and avoids the effects of photon recoil on the protected mode. A coherent state of motion whose parity is measured in this way will be projected into either an even or odd motional cat state, with the cat-state parity heralded non-destructively by the measurement. The parity can subsequently be verified by a second, destructive or non-destructive, measurement.

I will show results of critical steps needed to realize this protocol, including the entanglement of states on a single ion and on a multi-ion chain, Wigner function tomography of non-classical motional states on a single ion, and protection of the motional parity from detection by using motional mode-mode coupling on a multi-ion chain.

Speaker: Ingrid H. Zimmermann (University of Colorado Boulder)

32 Four- and six-photon stimulated Raman transitions for coherent qubit and qudit operations

We experimentally demonstrate transitions between electronic angular momentum states with a difference in magnetic quantum numbers $\Delta m_J$ = 3, 4, and 5 via resonant four- and six-photon stimulated Raman transitions in a single trapped atom. Derivation of the corresponding Rabi frequencies, which are verified experimentally, follows the standard treatment of two-photon transitions including the adiabatic elimination of intermediate states. We demonstrate a four-photon transfer fidelity of 96(1)% and discuss pathways to increase the observed multi-photon transition fidelities to >99.99%, providing a tool for efficient, high-fidelity control of qudits and single-atom logical qubits. Additionally, we measure ac Stark shifts up to eighth order in perturbation theory and speculate on potential applications to driving a two-qubit “light-shift” entangling gate on clock qubits and reducing crosstalk in individually-addressed qubit arrays.

Speaker: Gabriel Gregory (University of Oregon)

33 Entanglement of trapped-ion qubits over a 50 km-long fiber link

Quantum networks of registers of atoms have promising applications in cryptography, distributed computing, sensing, and clock synchronization. The realization of such networks requires the establishment of entanglement between atoms tens of kilometers apart. We recently performed an experiment to entangle two trapped atomic ions separated by 50 km of spooled optical fiber. Preliminary analysis of the data shows clear entanglement between the two ions. The entanglement is heralded by the detection of two photons – each collected from an ion using an optical cavity. In my presentation I will detail the experimental setup, give a quantitative analysis of our results in terms of the achieved Bell state fidelity and rates, and present our understanding of the main limiting factors. A key feature of our approach is the use of the two-photon click scheme, which does not require interferometric stabilization of the 50 km fiber path. Our results therefore open the door to robust metropolitan-scale networks of trapped-ion quantum processors, sensor arrays and clocks.

Speaker: Armin Winkler (Universität Innsbruck)

10:50 Coffee Break

Quantum Technologies

34 Remote Entanglement of Trapped Ions Using Integrated Photonics for Collection and Interference

Large-scale quantum processors will likely require modular architectures, and photon-mediated entanglement is a promising route to achieving high-fidelity interconnection using trapped ions. Current implementations rely on bulk photon-collection and interference optics, where mode-matching constraints and system-to-system variability impede scalability and limit the rates at which entangled pairs can be generated. To address these limitations, we demonstrate remote entanglement using an integrated photonics platform that enables passive phase stability, straightforward photonic manipulation, and intrinsic reproducibility. Specifically, we engineer waveguide-integrated gratings to couple photons emitted from trapped ions into single optical modes that are interfered on a multi-mode interferometer beam splitter within a microfabricated ion-trap chip, with detection of a single photon heralding entanglement between ions in separate trapping zones. The integrated collection gratings support straightforward multiplexing of remote entanglement in future devices. This demonstration could thus lay the foundation for scalable, high-rate, high-fidelity interconnects between modules of a distributed trapped-ion quantum computer.

Speaker: Sam Bishop (MIT)

35 Fabrication and Automated Characterisation of Optical Cavity Mirrors for Quantum Networking

To achieve high rates of entanglement generation in trapped ion quantum networks [1], the Purcell enhancement offered by optical cavities can be used to reach near-unit photon collection efficiency [2]. In this work, we address the challenges of fabricating and characterizing microcavity mirrors with ultralow, Å-level roughness, necessary to achieve high cooperativity in ion-cavity systems. We use focused ion beam (FIB) milling to produce features with state-of-the-art surface roughness for this size and scale [3,4]. To rapidly characterize these mirrors and to drive iterative improvements of the fabrication methods used, we design and build an automated cavity mode-matching experiment. An algorithm controls the degrees of freedom of a multi-axis stage (hexapod), on which the cavity is mounted. Using this method, we can achieve dominant coupling to the fundamental within the span of minutes, for a wide range of initial misalignments, and obtain the cavity finesse through automated measurements. These fabrication and characterisation developments offer a repeatable and scalable route to realising high finesse microcavities suitable for integration into ion trap network nodes.

1. L.J. Stephenson, et al., Phys. Rev. Lett. 124, 110501 (2020).
2. J. Schupp, PRX Quantum 2, 020331 (2021).
3. P. Maier, Opt. Express 33, 19205-19219 (2025).
4. A.A.P. Trichet et al., Opt. Express 13 17205-17216 (2015).

Speaker: Catherine Challoner (University of Oxford)

36 A Linear Ion Trap with Integrated Fiber Fabry–Perot Cavity for Distributed Quantum Computing

Distributed quantum computing with trapped ions is expected to rely on modular architectures in which many small ion registers are connected by photonic links [1]. In such a network, efficient ion–cavity coupling is crucial because it increases photon collection into a well-defined cavity mode and fiber channel, thereby boosting the remote-entanglement rate between modules. Short fiber Fabry–Perot cavities (FFPCs) are a promising route to this regime, but bringing dielectric mirrors close to the ion can introduce stray charging, trap distortion, and excess heating [2].
We present a combined hardware and fabrication approach toward compact, shielded ion–cavity interfaces for a linear ion trap. First, we developed a miniaturized, monolithic linear Paul trap for transverse FFPC integration, fabricated from gold-coated fused silica via selective laser etching [3]. The monolithic geometry removes post-fabrication electrode alignment, preserves trap symmetry, and provides large optical access while allowing conductive shielding of nearby cavity holders. Single 40Ca+ ions were successfully trapped, and the measured secular frequencies agree with finite-element simulations, yielding fitted imperfection factors of 0.96, 0.95, and 0.92 for the two radial and axial modes, respectively.
Second, we developed an adaptive CO2-laser machining method for fiber mirrors with in situ interferometric imaging [4]. The method updates multi-shot ablation patterns from the measured surface after each step. A key control parameter is the pause between shots, which tunes heat accumulation and therefore the lateral extent of each ablation event, enabling a controlled transition between global shaping and local correction. Using this approach, we fabricate Gaussian or near-spherical concave mirrors with radii of curvature of 250-700 µm, effective diameters of about 60 µm, and low ellipticity ($r_e < 0.2$) with close-to-unity yield. After high-reflectivity coating, the resulting FFPCs reach a finesse of $1.5 × 10^5$ at 854 nm and maintain $>10^5$ for cavity lengths up to 430 µm. These results provide key components for scalable, low-loss ion–photon interfaces in distributed trapped-ion quantum computing.

References

1. C. Monroe, R. Raussendorf, A. Ruthven, K. R. Brown, P. Maunz, L.-M. Duan, and J. Kim, Large-scale modular quantum-computer architecture with atomic memory and photonic interconnects, Phys. Rev. A 89, 022317 (2014).
2. H. Takahashi, E. Kassa, C. Christoforou, and M. Keller, Strong coupling of a single ion to an optical cavity, Phys. Rev. Lett. 124, 013602 (2020).
3. S. Teh, E. Kassa, S. Gao, S. Oya, and H. Takahashi, Ion Trapping with a Laser-written 3D Miniaturized Monolithic Linear Paul Trap for Microcavity Integration, arXiv:2409.05075 (2024).
4. S. Gao, V. Kavungal, S. Oya, D. Okuno, E. Kassa, W. J. Hughes, P. Horak, and H. Takahashi, Profile control of fiber-based micro-mirrors using adaptive laser shooting with in situ imaging, Opt. Express 33, 39009 (2025).

Speaker: Shuma Oya (Okinawa Institute of Science and Technology)

12:30 Lunch

Antimatter

37 Improved Precision for Hyperfine Spectroscopy of Magnetically Trapped Antihydrogen at ALPHA

Antihydrogen, the antimatter counterpart of hydrogen, provides a unique platform for testing fundamental symmetries in nature. One of its key properties, the ground-state hyperfine splitting (GSHFS), serves as a sensitive probe for Charge-Parity-Time (CPT) symmetry. In hydrogen, this splitting is known to a precision of 1.4 parts in 10¹² [1], offering a precise benchmark for comparison. As the GSHFS is also sensitive to nuclear structure, precise measurements in antihydrogen enable stringent tests of CPT symmetry through direct comparisons with hydrogen.

The ALPHA Collaboration, an international research team at CERN, leads efforts to investigate the fundamental properties of antihydrogen by producing and trapping antihydrogen atoms within a magnetic minimum trap for precision spectroscopy. One of ALPHA’s primary experimental efforts focuses on the GSHFS of antihydrogen, with the aim of performing precise comparisons with the well-known value in hydrogen. Previous measurements have yielded a value of 1,420.4 ± 0.5 MHz [3], limited primarily by statistics and magnetic field uncertainties. The introduction of Be⁺-assisted antihydrogen production, which vastly increases the production rate [4], combined with improved magnet control and characterization [5], has enabled significantly improved measurements of the GSHFS in antihydrogen.

This presentation will report on the most recent antihydrogen GSHFS measurements from the ALPHA experiment, highlighting the experimental method, achieved precision, and the outlook for future improvements in GSHFS spectroscopy at ALPHA.

References
[1] H. Hellwig, R. F. C. Vessot, M. W. Levine, P. W. Zitzewitz, D. W. Allan, and D. J. Glaze, “Measurement of the Unperturbed Hydrogen Hyperfine Transition Frequency,” IEEE Trans. Instrum. Meas., vol. 19, no. 4, pp. 200–209, Nov. 1970, doi: 10.1109/TIM.1970.4313902.
[2] V. A. Kostelecký and A. J. Vargas, “Lorentz and C P T tests with hydrogen, antihydrogen, and related systems,” Phys. Rev. D, vol. 92, no. 5, p. 056002, Sep. 2015, doi: 10.1103/PhysRevD.92.056002.
[3] M. Ahmadi et al., “Observation of the hyperfine spectrum of antihydrogen,” Nature, vol. 548, no. 7665, pp. 66–69, Aug. 2017, doi: 10.1038/nature23446.
[4] R. Akbari et al., “Be+ assisted, simultaneous confinement of more than 15000 antihydrogen atoms,” Nat. Commun., vol. 16, no. 1, p. 10106, Nov. 2025, doi: 10.1038/s41467-025-65085-4.
[5] R. Akbari et al., “The ALPHA-2 apparatus - facilitating experimentation with trapped antihydrogen,” Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip., vol. 1072, p. 170194, Mar. 2025, doi: 10.1016/j.nima.2024.170194.

Speaker: Jay Suh (University of Calgary)

38 Be+-Assisted Synthesis of Antihydrogen

The antihydrogen atom (the antimatter counterpart of a standard hydrogen atom) provides a unique testbed for probes of CPT invariance and the Weak Equivalence Principle (WEP) due to its mathematical simplicity and neutral charge respectively. However, prior to performing any such tests the antiatoms must first be synthesised from their constituent particles.
Presented here are the recent developments in antihydrogen synthesis and trapping made by the ALPHA collaboration in both the ALPHA-2 and ALPHA-g experiments. Novel techniques first reported in [1], (and implemented in ALPHA-2) use laser cooled $\mathrm{Be^{+}}$ ions to sympathetically cool $\mathrm{e^{+}}$ plasmas to around 7 K, compared to 18 K without $\mathrm{Be^{+}}$ ions. The resulting synthesis produces antihydrogen at lower temperatures thereby confining a larger fraction of the produced population within ALPHA’s magnetic minimum trap. Despite only trapping around 0.05% of the produced antihydrogen, ALPHA can repeat the synthesis cycle an arbitrary number of times and is now regularly able to accumulate samples over $10^{4}$ atoms.
Near-linear increases in the antihydrogen trapping with the number of antiprotons used in synthesis have further revealed that the sympathetic cooling provided by the $\mathrm{Be^{+}}$ ions not only reduces the $\mathrm{e^{+}}$ plasma temperature but also help to maintain it throughout synthesis. This additional cooling power counteracts the inherent heating rates associated with the merge of the antiproton and positron plasmas as well as heating due to patch potentials on the electrode surfaces and the radial octupole magnetic field (which provides radial confinement of the antihydrogen atoms in the magnetic trap). [2]
The effects of other parameters that contribute to the 3-body recombination reaction underlying antihydrogen formation at ALPHA [3] such as $\mathrm{e^{+}}$ density, $\mathrm{e^{+}}$ temperature and the shape of the magnetic minimum trap fields have also been studied in efforts to maximise the antiatom yield.
In 2024, the $\mathrm{Be^{+}}$ system was fully integrated into the ALPHA-g experiment where, as expected, it immediately outperformed the traditional synthesis reported in [4]. At present, the collaboration is able to obtain antihydrogen populations comparable to those in ALPHA-2 in the ALPHA-g machine.
The significant increase in antiatom availability for experiments is a paradigm shift in ALPHA’s capabilities which in the future may permit ALPHA to perform stronger tests of CPT invariance via precision spectroscopy of antihydrogen[5] (in the ALPHA-2 apparatus), as well as further probes of the Weak Equivalence Principle through future gravity release protocols (in the ALPHA-g machine).

[1] Akbari, R., de Araujo Azevedo, L.O., Baker, C.J. et al. Be+ assisted, simultaneous confinement of more than 15000 antihydrogen atoms. Nat Commun 16, 10106 (2025)
[2] Goncalves, Maria. Be+-Assisted Antihydrogen Synthesis and Trapping. Swansea, 2026.
[3] Zammit, M. et al. Antihydrogen Chemistry, Phys. Rev. A 111, 050101 (2025)
[4] Anderson, E.K., Baker, C.J., Bertsche, W. et al. Observation of the effect of gravity on the motion of antimatter. Nature 621, 716–722 (2023)
[5] Baker, C.J., Bertsche, W., Capra, A. et al. Precision spectroscopy of the hyperfine components of the 1S–2S transition in antihydrogen. Nat. Phys. 21, 201–207 (2025)

Speaker: Tom Robertson-Brown (Swansea University)

39 Developments of BASE Hannover towards quantum logic spectroscopy of the (anti-)proton g-factor

In our cryogenic multi-Penning trap experiment, we aim to contribute to high-precision (anti-)proton $g$-factor$^{[1,2]}$ measurements pursued by the BASE collaboration, providing stringent tests of CPT symmetry$^{[3]}$. To reach precision at the parts-per-trillion level and to gain access to SME coefficients currently unreachable with existing techniques, we are implementing techniques based on quantum logic spectroscopy (QLS)$^{[4,5]}$, where both sympathetic cooling and spin-state detection of the (anti-)proton are mediated with a single $^{9}\mathrm{Be}^{+}$ ion. This will be achieved by coupling the particle motions via Coulomb interaction in a double-well potential.

In a previous experimental phase, we demonstrated several key QLS prerequisites in Penning traps, including optical sideband spectroscopy$^{[6]}$, ground-state cooling$^{[7]}$ of a single $^{9}\mathrm{Be}^{+}$, and fast adiabatic transport$^{[8]}$. In this contribution, we report on our current status, including the implementation of a new Penning trap stack. Within this setup, we aim to load protons, and achieve motional coupling between two $^{9}\mathrm{Be}^{+}$ ions in a symmetric double-well potential. This configuration serves as a proof-of-principle demonstration in which both particles are laser-accessible, before extending the scheme to the coupling of a $^{9}\mathrm{Be}^{+}$ ion to the (anti-)proton in an asymmetric double-well potential due to the 9:1 mass ratio of the particles.

Finally, we highlight recent developments for the future experimental phase, where we aim to sympathetically cool the (anti-)proton. We show simulations$^{[9]}$ describing the proposed cooling scheme, along with progress in the development of a microfabricated coupling trap where this cooling will be implemented. We also show that this cooling scheme could be applied to the vibrational spectroscopy molecular (anti-)hydrogen ions$^{[10]}$.
[1] G. Schneider et al., Science 358 (2017).
[2] C. Smorra et al., Nature 550 (2017).
[3] R. Lehnert, Symmetry 8 (2016).
[4] D. J. Heinzen and D. J. Wineland, Phys. Rev. A 42 (1990).
[5] P. O. Schmidt et al., Science 309 (2005).
[6] J. M. Cornejo et al., Phys. Rev. Res. 5 (2023).
[7] J. M. Cornejo et al., Phys. Rev. Res. 6 (2024).
[8] M. v. Boehn et al., Comms. Phys. 8 (2025).
[9] N. Poljakov et al., arXiv:2602.22826 (2026).
[10] S. Schiller et al., in review (2026).

Speaker: Nikita Poljakov (Leibniz Universität Hannover, Germany)

Quantum Computing

40 Quantum information processing using 176Lu+ Qudits

Extending the computational Hilbert space, we encode qudits in the magnetically insensitive hyperfine states in the 3D1 manifold of Lutetium ions. Equipped with error-suppressing pulses through optimized dynamical modulation of optically driven couplings, this is designed to implement universal control for qudit quantum information processing. Additionally, the system can co-trap ytterbium ions, enabling exploration of practical applications such as quantum non-demolition measurements [1], quantum-logic-assisted syndrome readout protocols, and quantum simulations for chemistry [2].

1. D. Hume et al., Phys. Rev. Lett. 99, 120502 (2007).
2. R. J. MacDonell et al., Chem. Sci., 2021,12, 9794-9805 (2021).

Speaker: Prachi Nagpal (University of Sydney)

41 Native polyqubit gate mediated by multi-tone drive

The leading approach to increase the computational capabilities of an ion-trap quantum computer is to increase the number of ions in the device. Employing multi-level systems, however, also significantly increases the Hilbert space dimension but with less hardware overhead. In trapped ions, multi-level systems can be made, for example, by using more atomic states or by harnessing the harmonic modes of motion of the chain. The multiple levels can be treated either as one large base-$d$ register (known as qudits) or as multiple base-2 qubits (known as polyqubits or virtual qubits).$^1$ While the two interpretations are equivalent, the theoretical and experimental study of qubits is much more mature than that of qudits. Interpreting each ion as multiple qubits might provide more insight and intuition.

Manipulating a multi-level system is technically challenging. Driving gates within a single multi-level system requires control of multiple tones: at least $d-1$ tones are needed to address a $d$-level system. Generating these tones is experimentally complex, especially in certain use cases where they must be phase-locked to each other. The tones are usually driven sequentially, and switching between them exposes the system to errors that don't appear in qubit devices.$^2$ Each pair of states within the polyqubit must remain phase coherent with its driving tone, so any phase that is accrued while that transition is not addressed must be tracked and corrected.

We present a novel approach to driving individual qubits in a polyqubit that addresses the sources of error inherent to single-tone gate schemes. We also provide an implementation of this gate in a polyqbuit with two qubits stored in a single $^{137}$Ba$^+$ ion across the ground $S_{1/2}$ and metastable $D_{5/2}$ levels. Our multi-tone technique directly drives single-qubit gates with one pulse, compared to single-tone schemes which use multiple two-qubit gates to construct single-qubit gates. In our polyqubit gate, all tones are driven at the same time, creating a closed-contour interaction$^{3,4}$. The tones interfere with each other to create the desired dynamics that drive a single-qubit gate. Choosing whether to drive one qubit versus the other can be done in software by simply updating the relative phases of the tones. This technique leverages the unique features of multi-level systems instead of using techniques originally developed for two-level systems to create a more native polyqubit gate.

References
[1] Shivam et al., arXiv:2406.19332 (2024).
[2] A. Vazquez-Brennan, PhD thesis. Manuscript in preparation (2026).
[3] Buckle et al., Optica Acta: International Journal of Optics, 33(9), 1129–1140 (1986).
[4] Barfuss et al., Nat. Phys. Volume 14, 1087–109 (2018).

Speaker: Sophie Decoppet (University of Oxford)

15:10 Coffee Break

Quantum Technologies

42 Trapped ions as a platform for quantum communication over an urban fiber link

Large-scale quantum networks provide the basis for many potential quantum communication applications, such as quantum key distribution (QKD) and distributed quantum computing. Due to the widespread availability of telecom fibers used in classical communication, these could serve to implement such networks over potentially several hundred kilometers by encoding and sending quantum information via photons. Using long fiber-based networks also provides challenges such as environmentally induced polarization drifts, high losses due to splices, and the ability to interface different types of quantum memories.
We report on the realization and characterization of a 14 km-long quantum communication fiber testbed as well as the implementation of several quantum network protocols based on a single $^{40}$Ca$^+$ ion as a quantum memory. Due to an exposed above-ground section, a fast and automated polarization drift compensation is implemented that allows us to maintain ~99% process fidelity .
Using the $^{40}$Ca$^+$ ion and an ion-resonant photon-pair source, we demonstrate entanglement distribution with up to ~$99\,\%$ fidelity and atom-to-photon quantum state teleportation [1] with an average fidelity of ~$84\,\%$ over the fiber link [2]. To reduce transmission loss, we utilize quantum frequency conversion from the ionic wavelength of $854\,$nm to $1550\,$nm [3].
We also demonstrate the conversion of atom-photon entanglement from polarization to time-bin encoding in order to enable interfacing dissimilar quantum memories, such as ions and color centers. We use a fiber-based telecom encoding and analyzer setup with active phase and temperature stabilization with a conversion fidelity of $97.8\,\%$. The resulting converted atom-photon entanglement fidelity is $70.4\,\%$ compared to $93\,\%$ without conversion to time-bin. The reduction is mainly due to a low signal-to-background ratio and long-term drifts in the setup.
We also demonstrate a device-independent quantum key distribution protocol [4] based on atom-photon entanglement over an emulated fiber link of $20\,$km length. We also include quantum frequency conversion to telecom and back to the ion wavelength, as well as automated polarization compensation and classical communication to show the viability of the protocol for the actual fiber testbed.

[1] E. Arenskötter et al., Phys. Rev. Research 6, 023061 (2024)

[2] S. Kucera et al., npj Quantum Inf. 10, 88 (2024)

[3] E. Arenskötter et al., npj Quantum Inf 9, 34 (2023)

[4] R. Schwonnek et al., Nat. Commun. 12, 2880 (2021)

Speaker: Christian Haen (Universität des Saarlandes)

43 Experimental Characterization of Normal Modes in Planar Ion Traps by Selective Mode Excitation

Our group has demonstrated the trapping of parallel chains of ${}^{40}\mathrm{Ca}^+$ ions using a planar-electrode ion trap. By applying two radio-frequency (RF) voltages, a double-well potential is generated, and the distance between ion chains can be controlled by adjusting the ratio of these RF voltages. Ideally, the trapping potential is perfectly harmonic for a one-dimensional ion chain. In practice, however, distortions arise from stray electric fields and electrode asymmetries. These effects become more pronounced in double-well configuration, where more complex electrode structures are required. In this study, we characterize the trapping potential from ion imaging data by extracting higher-order motional eigenmodes. To this end, we develop and demonstrate techniques to optically excite motional modes and perform time-resolved imaging. These methods provide access to higher-order modes and their phase information, enabling detailed characterization of stray fields and nonlinear components of the trapping potential. These techniques are expected to enable accurate estimation of trapping potentials via the mode-structure measurements, extending beyond harmonic confinement to anharmonic potentials and two-dimensional ion configurations.

We define the direction along which ions align in a single chain as the $z$-axis. For a system of $N$ ions confined in a harmonic potential, the total potential consists of the harmonic confinement and the Coulomb interaction between ions. This system exhibits $N$ normal modes of vibration along the $z$-axis. The curvature of the harmonic potential corresponds to the eigenvalue of the fundamental motional mode, known as the center-of-mass (COM) mode, in which all ions oscillate in phase with equal amplitude.

There are two primary methods for measuring motional frequencies. One method is based on sideband spectroscopy, which identifies modes from carrier and sideband transitions, but requires highly stable lasers and precise spectroscopic techniques. The other method is electrical “tickling,” in which forced oscillations are induced by applying an AC signal to a DC electrode. By detecting resonance, the eigenfrequency of a mode can be determined. This method is widely used due to its simplicity; however, because it generates a global excitation field acting on the entire ion chain, it becomes increasingly difficult to excite higher-order modes due to the asymmetry of their eigenvectors. To overcome this limitation, we investigate an alternative approach termed optical tickling, in which motional modes are excited via amplitude modulation of the cooling laser. By individually addressing ions, a localized excitation field is generated, enabling efficient excitation of all normal modes, including higher-order modes that are difficult to access electrically. In parallel, we are developing a time-resolved imaging technique capable of measuring eigenvectors of the excited modes with phase resolution. We have demonstrated this method for COM and stretch modes by using an acousto-optic modulator as a fast optical shutter. In this presentation, we report recent progress in the excitation of higher-order motional modes using optical tickling and their characterization via time-resolved imaging.

Speaker: Ryosuke Nishimoto (University of Osaka)

44 Quantum computing with X- junction for 2D navigation of trapped ion qubits

Quantum computing with X- junction for 2D navigation of trapped ion qubits

*> S. Mohandas, A. Conta, J. Müller, U. G. Poschinger, and F. Schmidt-

Kaler*

QUANTUM, Institute of Physics, 55128 Mainz, Germany

Trapped-ion quantum processors are currently transitioning from proof-of-concept laboratory experiments to robust, scalable, and user-ready devices. A critical requirement for large-scale computation, particularly within a Quantum Charge-Coupled Device (QCCD) architecture, is the ability to dynamically shuttle ions through multi-zone, micro-structured trap arrays. Leveraging advanced trapped ion control electronics, our team at Johannes Gutenberg University Mainz (JGU) is refining the reliable transport of ion crystals across complex trap junctions.
We utilize a segmented X-trap which is fabricated in our own clean room via Selective Laser Etching (SLE). Fully sculptured trap geometry has been meticulously engineered and scaled down to optimize radiofrequency (RF) requirements, mitigate anomalous heating, and minimize stray capacitance. The design features a central X-junction equipped with a split bridge to facilitate highly controlled transport. The voltage protocols driving this transport are generated using a recently developed numerical toolchain tailored for fast, low-excitation ion shuttling in segmented trap [1]. Based on a precise electrostatic model of our trap electrode geometry, this framework combines an electrostatic field solver with efficient unconstrained optimization and dynamical simulations of ion motion. It computes time-dependent voltage waveforms that realize prescribed transport trajectories across the junction while strictly adhering to real-world experimental constraints.
Here, I describe the experimental setup in detail. Moreover, I sketch the sequence comprising initial ground-state preparation via sideband cooling, followed by the transport of an ion crystal across the X-junction to benchmark the performance of both the SLE trap and the computed waveforms. Important characterizations include the measurement of the motional excitation per round trip. The X-trap will eventually serve to distribute qubit entanglement in a scalable 2D quantum computing architecture.

Reference

1. Conta, Andreas, Santiago Bogino, Frodo Köhncke, Ferdinand Schmidt-Kaler, and Ulrich Poschinger. "Toolchain for shuttling trapped-ion qubits in segmented traps." arXiv preprint arXiv:2601.08495 (2026).

Speaker: Salvi Mohandas (Johannes Gutenberg-Universität Mainz,Germany)

45 Switchable low-noise permanent magnet gradients for long-wavelength trapped-ion quantum information.

Static magnetic field gradients can be used to couple the spin and motional states of trapped-ions, allowing for two-qubit gates using long-wavelength radiation. The use of permanent magnets to create such gradients give rise to much better noise specifications than the use of current carrying wires (CCWs), enabling much higher entanglement fidelities while reducing the required power consumption. The desire for scalability, as well as the need to switch fields off between gate and shuttling operations, has led to the development of trap-integrated current carrying wire methods of gradient generation. Gradients produced by CCWs inevitably introduce current-dependant noise which must be mitigated with bulky low-noise current supplies. We present a method of generating magnetic field gradients with a novel magnetic field switching system. This “Saturable Electronic Reluctance Switch” (SERS) allows the field of a permanent magnet to be switched on and off by application of a current, but without any current dependence at the output field. This allows for fully stable output field akin to a permanent magnet allowing for high-fidelity two-qubit gates, but with the ability to switch the field on and off for shuttling operations within a QCCD architecture. This method is the first bi-stable magnetic field switch, and can find applications in other areas of atomic and molecular physics such as micro-NMR imaging and neutral atom traps.

Speaker: Caleb Burhan (University of Sussex)

Social: Conference Dinner

Friday 11 September

Clocks and Precision Spectroscopy

46 A transportable Al+ quantum logic optical clock

Optical atomic clocks are the most precise measurement tools, achieving fractional frequency uncertainties below $10^{−18}$. Transportable systems can extend this accuracy to a broader range of applications. High-precision frequency ratio measurements are essential to validate clock accuracy and ensure consistency across platforms – a key requirement towards the redefinition of the SI second. Transportable systems allow these comparisons on-site at various metrology institutes when a connecting fiber link is missing. Furthermore, transportable optical clocks can be used for relativistic geodesy as they allow height difference measurements on the cm level over large distances.
Our fully rack-integrated clock setup is based on the $^1𝑆_0\rightarrow {^3𝑃_0}$ transition in $^{27}\mathrm{Al}^+$. A co-trapped $^{40}\mathrm{Ca}^+$ ion allows for sympathetic cooling and state detection through quantum logic spectroscopy. We present the results of our investigation of various frequency shifts in our optical clock. Furthermore, we present ground state cooling, quantum logic spectroscopy, and our progress towards clock operation.

Speaker: Joost Hinrichs (Leibniz University Hannover & Physikalisch-Technische Bundesanstalt)

47 Development of a Second ¹⁷¹Yb⁺ Ion Optical Clock at NPL Towards the Redefinition of the SI Second

Optical frequency standards now surpass caesium frequency standards in accuracy and stability, forming the motivation for the future redefinition of the SI second [1]. Key requirements for the redefinition are the validation of uncertainty budgets at the level of ≲ 2 × 10⁻¹⁸ and agreement between independent optical frequency ratios at uncertainty ≲ 5 × 10⁻¹⁸. The ¹⁷¹Yb⁺ optical clock at the National Physical Laboratory (NPL), based on the electric octupole (E3) transition (NPL-E3Yb+3), has demonstrated the first of these requirements through systematic evaluations reported in [2], achieving a total fractional systematic uncertainty of 2.2 × 10⁻¹⁸. Recent improvements in NPL-E3Yb+3, including reduced systematic uncertainties, longer coherence times of the atom–laser interaction, and increased operational uptime have reduced the overall measurement uncertainties still further. Local comparisons with the strontium optical frequency standard at NPL (NPL-Sr1) and remote comparisons with European optical frequency standards have now demonstrated measurement uncertainties at the required level of 5 × 10⁻¹⁸. These results represent significant progress towards fulfilling the criteria for redefining the second.

To extend capability, a second ¹⁷¹Yb⁺ optical clock is under construction at NPL, and we report progress on its development. The new system is based on an updated end-cap ion trap [3] with a redesigned RF feed-through that reduces capacitance to the vacuum chamber, suppressing RF dielectric heating and the associated temperature rise. This will improve control of black-body radiation shifts and support trap-related fractional uncertainties below 10⁻¹⁸. The setup also incorporates a multi-layer magnetic shield with a shielding factor of ~1000 to suppress the ambient field fluctuations. This enhanced stability enables the operation of the E3 clock on Zeeman-sensitive transitions, cancelling the electric quadrupole shift and reducing the associated uncertainty in the second-order Zeeman shift. In addition, automated beam alignment will be implemented using piezo-actuated translation stages to increase operational robustness and unmanned operation. The second Yb+ system will enable a direct comparison with the first, providing a rigorous test of calculated systematic uncertainty budgets and supporting frequency ratio measurements at the low 10⁻¹⁸ level of uncertainty.
References

[1] N. Dimarcq et al., “Roadmap towards the redefinition of the second”, Metrologia, vol. 61, p. 012001, 2024.
[2] A. Tofful et al., “171Yb+ optical clock with 2.2 × 10-18 systematic uncertainty and absolute frequency measurements”, Metrologia, vol. 61, p. 045001, 2024.
[3] P. B. R. Nisbet-Jones et al., “A single-ion trap with minimized ion–environment interactions”, Appl. Phys. B vol. 122, 57, 2016.

Speaker: Thilina Senaviratne (National Physical Laboratory)

48 A Penning trap single-photon counter for axion detection

The Quantum enhanced particle astrophysics (QuEPA) project attempts to use an electron Penning trap as one part of a detector for axion dark matter [1]. Axions emerged as a dark matter candidate after initially being proposed to resolve the observed lack of charge parity (CP) violation in the strong interaction. Axions can convert into microwave photons in the presence of a strong magnetic field due to their coupling to the electromagnetic field [2]. A microwave single photon counter dramatically improves the scanning rate of an axion detector [3]. As no technology currently exists to efficiently detect photons in the frequency band of 30-60 GHz, we propose the use of a single electron in a Penning trap as a microwave photon counter. Incoming photons are absorbed by the electron's cyclotron motion, which, through the continuous Stern-Gerlach effect, produces a detectable phase shift in the axial oscillation.

In this session, we present an update on the progress towards realising this detector. We have designed and built a novel cryogenic Penning trap system housed within a dilution refrigerator capable of reaching temperatures below 50 millikelvin. We have developed a custom impedance-matched image-current detection system featuring GaAs semiconductor switches, allowing electronic switching between detection and cooling modes, laying the groundwork for cooling the electron below its ambient temperature. We have successfully trapped clouds of around 500 electrons on demand and are currently performing initial trap characterisation measurements, with preliminary dark matter searches and phase-sensitive detection of the axial motion as the next steps.

[1] J. A. Devlin, M. L. Wojtkowiak, S. R. Banhatti, H. Zhang, J. Shi, T. S. Dofher, J. M. H. Gosling, M. R. Tarbutt, and R. C. Thompson, A Penning trap single-photon counter for axion detection, arXiv:2601.05472 (2026).

[2] I. G. Irastorza and J. Redondo, New experimental approaches in the search for axion-like particles, Prog. Part. Nucl. Phys. 102, 89 (2018).

[3] S. K. Lamoreaux, et al., Phys. Rev. D 88, 035020 (2013).

Speaker: Marko Wojtkowiak (Imperial college London)

49 Implementation of a Josephson Voltage Standard for the First Direct Measurement of the Nuclear Magnetic Moment of $^{3}$He$^{2+}$

The first direct high-precision measurement of the magnetic moment of the bare $^{3}$He$^{2+}$ nucleus requires resolving minuscule spin-flip-induced axial frequency shifts of the order of $50\, \text{mHz}$, a factor of $400$ smaller than observed for $^{3}$He$^{+}$ ions [1]. This challenging measurement will be performed on a single ion confined in a Penning trap at MPIK.
Current axial frequency stability is limited, amongst others, by the stability of the state-of-the-art commercial voltage source, the UM1-14, which enables relative frequency stabilization at a level $2\cdot 10^{-8}$ [2], corresponding to several tens of $\text{mHz}$.
To overcome this limitation, we replace the UM1-14 with a $1\, \text{V}$ programmable Josephson Voltage Standard (PJVS), built at PTB Braunschweig. Based on the inverse AC Josephson effect, the PJVS generates a voltage that depends solely on the irradiation frequency of the Josephson junctions and fundamental constants which are fixed to exact values in the SI system. This eliminates dependencies on junction geometry, temperature, and other experimental conditions. This near-ideal frequency-to-voltage conversion is expected to improve axial frequency resolution by at least a factor of two.
We present progress in the integration and characterization of the PJVS, report stability measurements and outline the timeline toward achieving the first direct determination of the $^{3}$He$^{2+}$ magnetic moment.

References:
[1] Schneider et al., Nature 606, 878–883 (2022).
[2] Kaiser et al., Appl. Phys. Lett. 124, 224002 (2024).

Speaker: Mr Felix Grüner (MPI Nuclear Physics, Heidelberg, Germany)

10:50 Coffee Break

Quantum Computing

50 Progress on room-temperature microwave-driven two qubit quantum processor

Our group develops scalable ion-trap quantum computers based on the Charge-Coupled Quantum Device (QCCD) architecture. To realize elementary quantum gate operations on the trapped-ion qubits, we employ the microwave near-field approach [1] which uses microwave conductors embedded in the trap structure and the resulting amplitude gradients of the microwave magnetic field. This poster reports on results from a room-temperature surface-electrode ion trap apparatus, which we employ to develop new gate schemes and qubit control techniques. The setup employs $^9\text{Be}^+$ ions in a surface-electrode ion trap. We have recently demonstrated a universal computation register based on amplitude-modulated two-qubit microwave gates and micromotion-sideband single-ion addressing [2]. We report on important experimental upgrades to this setup, including a new control system and an individual-ion real-time capable readout, which significantly enhances our gate analysis capability, as well as novel multi-qubit gate schemes. This work has been supported by the QVLS-Q1 project, the BMFTR ATIQ project and the EU Millenion-SGA1 project.

[1] C. Ospelkaus et al., Nature 476 7359 (2011)
[2] N. Pulido-Mateo et al.,Phys. Rev. Research 6, 2 (2024)

Speaker: Alexander Onkes (Leibniz Universität Hannover, Physikalisch-Technische Bundesanstalt)

51 Enabling mid-circuit measurement and readout with trapped barium ions

Mid-circuit measurement and readout (MCMR) are essential requirements for fault-tolerant trapped-ion quantum computers, as they enable syndrome measurement and feedback in quantum error correction protocols. Implementing these operations on auxiliary qubits in single-species trapped ion crystals remains challenging, as photon absorption due to resonance-fluorescence detection can introduce significant decoherence in nearby data qubits. In this work, we investigate a simplified MCMR architecture with trapped barium ions that utilises tightly focused, far off-resonant lasers combined with a global beam that couples to the $6S_{1/2} \rightarrow 5D_{3/2}$ transition at 2051 nm in Ba$^+$. We propose to mitigate decoherence in data qubits by implementing background-free detection of the auxiliary qubits with the 2051 nm laser, after which the auxiliary qubits can be cooled via mid-sequence sideband cooling with the same laser. To support stable operation, we perform frequency stabilisation of the 2051 nm laser via locking to an optical frequency comb. Ultimately, this work supports the implementation of MCMR and mid-sequence cooling in single-species quantum processors.

Speaker: Phoebe Grosser (Universität Innsbruck)

52 Beyond squeezing: applications of generalized squeezing in hybrid spin-oscillator quantum information processing

Squeezing and displacement of a bosonic mode are well-known operations with a wide range of applications in quantum information processing (QIP), from two-qubit gates [1] to precision metrology [2]. Generalized, higher-order spin-dependent squeezing interactions in hybrid spin-oscillator systems have recently come under experimental control [3,4], and represent a novel, rich, and under-explored resource for QIP. Here we discuss one of several applications of these interactions: genuine N-body spin interactions mediated by individually addressed spin-dependent generalized squeezing, which allow for efficient construction of large-scale Toffoli gates and many-body Hamiltonians. We report two strategies to generate N-body gates and their duration in trapped-ions.

[1] R. Srinivas, et al., "High-fidelity laser-free universal control of trapped ion qubits," Nature 597, 209 (2021).
[2] J. Aasi, et al., "Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light," Nat. Photonics 7, 613 (2013).
[3] O. Băzăvan, S. Saner, et al., "Squeezing, trisqueezing, and quadsqueezing in a spin-oscillator system," arXiv:2403.05471 (2024). Accepted to Nat. Phys.
[4] S. Saner, O. Băzăvan, et al., "Generating arbitrary superpositions of nonclassical quantum harmonic oscillator states," arXiv:2409.03482 (2024).

Speaker: Kai Shinbrough (University of Oxford)

53 Trapped-Ion Quantum Computing Setup Joining Shuttling- and Addressing-Based Architecture

To enhance the capabilities of trapped-ion quantum computers, systems possessing hundreds of qubits are required. In pursuit of this objective, our system combines single-ion addressing with the transport of ion chains in a micro-segmented Paul trap [1]. Our setup will feature two independent laser addressing zones, each capable of performing quantum gates, while shuttling facilitates connectivity between the ions in the two zones [2]. Each zone is designed to address a ten-ion chain, and the segmented electrode architecture allows additional chains to be stored between the addressing regions. This design therefore has the potential to perform quantum algorithms involving multiple chains of ten qubits. Addressing is implemented using a crossed-AOD system, enabling fast beam steering without shifting the beam frequency [3]. The addressing design was simulated to provide a tightly focused beam with minimal aberrations along the entire ion chain, resulting in low nearest-neighbour intensity crosstalk. To improve coherence times, the system will be housed in three layers of mu-metal shielding to suppress magnetic field fluctuations, and the quantisation axis is generated by a temperature-stabilised Halbach coil configuration. This poster presents the current progress on the system, including characterisation measurements of the trap frequencies, qubit and motional coherence times, as well as the motional heating rates. We further compare the simulated and measured addressing crosstalk, as well as the beam profiles for all ten ions.

[1] Ruster, T., et al. Experimental realization of fast ion separation in segmented Paul traps. Physical Review A, 90(3), p.033410, 2014.
[2] Kreppel, F., et al. Quantum circuit compiler for a shuttling-based trapped-ion quantum computer. Quantum, 7, p.1176, 2023.
[3] Chen, Y.L., et al. Low-crosstalk optical addressing system for atomic qubits based on multiple objectives and acousto-optic deflectors. Physical Review Applied, 22(5), p.054003, 2024.

Speaker: James Rumbold (Johannes Gutenberg University)

Closing

13:00 Lunch

Social: Activities