Time in Quantum Theory (TiQT) 2026

25 May 2026, 09:00 → 28 May 2026, 12:00 Europe/Stockholm

Albano 3: 4204 - SU Conference Room (56 seats) (Albano Building 3)

Viktoria Kabel (ETH), Magdalena Zych (Stockholm University), Sebastian Schuster (Stockholm University), Sara Butler (Stockholm University), Tara Michele Fortier (NIST), Francesca Vidotto (IEM-CSIC), Aephraim Steinberg (University of Toronto)

We are pleased to announce the 2026 edition of Time in Quantum Theory, which will take place on 25–28 May 2026 at Stockholm University.

 

The TiQT conference series brings together researchers from theoretical physics, experimental physics, and philosophy to exchange ideas on the nature of time in quantum theory and related areas.

 

 

Topics of interest include:

 

• fundamental limits of timekeeping
• foundational, operational, and experimental approaches to temporal measurement
• relativistic and gravitational effects
• quantum clocks and reference frames
• causality and temporal structure
• thermodynamics and the arrow of time
• philosophical perspectives on time in quantum theory

 

Confirmed speakers include:

 

• V. Vilasini  (Inria, Université Grenoble Alpes)
• Eddy Chen (University of California San Diego)
• Lucy James (University of Bonn)
• Joshua Foo (Kyushu University)
• Jan Klärs (University of Twente)
• Leon Loveridge (University of South-Eastern Norway)

 

Registration is currently closed. 

 

The conference is organized under Working Group 3 of the COST Action 23115 on Relativistic Quantum Information (RQI). COST is an EU-funded programme supporting scientific collaboration and training across its member states. Further information about the Action is available at https://rqi-cost.org. Interested participants are also welcome to join the Action as members.

There will also be a linked summer school on "Time, Memory, and Causality in Quantum Physics" the week before (18.–23.5.2026), as part of this COST Action. Especially junior participants are warmly welcomed to register for both events!

 

There will also be a social event on Saturday, 23 May, co-organized with the COST RQI School. More information to come!

 

Previous editions of TiQT

• 2025, Genoa, Italy: https://tiqt2025.quantummechanics.it/
• 2024, Smolenice, Slovakia: http://quantum.physics.sk/tiqt2024/
• 2023, Westport, Ireland: https://www.tocqs.com/tiqt
• 2022, Vienna, Austria: https://tqt2022conference.wordpress.com/
• 2021, Zurich, Switzerland: https://timequantum.phys.ethz.ch/

 

Monday 25 May

09:00 → 09:20 Welcome

09:20 → 12:00 Relativistic Quantum Information

Chair: Magdalena Zych

09:20 Quantum signatures of proper time in optical ion clocks

Optical clocks based on atoms and ions probe relativistic effects with unprecedented sensitivity. They resolve time dilation due to atom motion or different positions in the gravitational potential through frequency shifts. However, all measurements of time dilation so far can be explained effectively as the result of dynamics with respect to a classical proper time parameter. Here we show that atomic clocks can probe effects where a classical description of the proper time dynamics is insufficient as superpositions of proper time emerge. We apply a Hamiltonian formalism to derive time dilation effects in harmonically trapped clock atoms and show how second-order Doppler shifts due to the vacuum energy, squeezing, and quantum corrections to the dynamics arise. We also demonstrate that time-dilation-induced entanglement between motion and clock evolution can become observable in state-of-the-art clocks when the motion of the atoms is strongly squeezed, realizing proper time interferometry. Our results show that experiments with trapped ion clocks are within reach of probing relativistic evolution of clocks for which a quantum description of proper time becomes necessary.

Based on G. Sorci, J. Foo, D. Leibfried, C. Sanner, I. Pikovski, Phys. Rev. Lett. 136, 163602 (2026).

Speaker: Dr Joshua Foo (Kyushu University)

10:00 The time-energy uncertainty relation in quantum field theory

The time-energy uncertainty relation is often invoked as a heuristic explanation for virtual particles in interacting quantum field theory. However, this interpretation breaks down upon closer scrutiny for several reasons. Although concrete derivations and interpretations of time-energy uncertainty bounds in quantum mechanics have been established, most famously by Mandelstam and Tamm in 1945, there is no known rigorous connection between these bounds and the concept of virtual particles in quantum field theory. In this work, we show that virtual excitations associated with subcycle modes of a free scalar field can be converted into real excitations of an idealized mode-selective probe coupled to the field. Defining the time uncertainty as the effective duration of the probe-field interaction, we show that a time-energy uncertainty relation is satisfied in the deep subcycle regime. Our results provide concrete operational meaning to the textbook heuristic picture of virtual particles in quantum field theory in terms of the time-energy uncertainty principle.

Speaker: Mr Achintya Sajeendran (University of Queensland)

10:20 Coffee Break

11:00 Time-Resolved Signatures Of Observer-dependent Vacuum Fluctuations with Coherently Interacting Emitters

Time in quantum theory is operational, it is inferred from physical processes used as clocks and from temporal correlations registered by quantum systems. The Unruh effect is a striking manifestation of this idea, uniform acceleration changes the detector's notion of time and yields a thermal response in vacuum, linking time and motion. We developed time-resolved approach to detect Unruh effect using cavity QED and coherently interacting two-level atoms. In an open system framework where acceleration and boundaries enter through two-point correlation function of field, finite cavity quality factor reshapes temporal correlations, modifying cooperative decay and coherent interactions. In superradiant regime these changes become visible in timing and width of emission burst, providing operation probe of observer dependent vacuum fluctuations.

Speaker: Mr Akhil Deswal (Indian Institute of Science Education & Research (IISER))

11:20 Superluminal Transformations and Indeterminism

Quantum theory is widely regarded as fundamentally indeterministic, yet classical frameworks can also exhibit indeterminism once infinite information is abandoned. At the same time, relativity is usually taken to forbid superluminal signalling, yet Lorentz symmetry formally admits superluminal transformations (SpTs). Dragan and Ekert have argued that SpTs entail indeterminism analogous to the quantum type. Here, we prove a no-go theorem based on natural assumptions of consistent causal embedding of events across reference-frame transformations in a world with finite information. One way to interpret this is that superluminal transformations (SpTs) and finite information cannot coexist. Any theory accommodating SpTs must therefore allow unbounded information content, leading to a deterministic ontology akin to that of classical theories formulated over the real numbers. Thus, any apparent indeterminism arising from superluminal transformations reflects only probabilities arising from subjective ignorance, unlike the objective nature of probabilities in quantum theory, indicating that the claimed indeterminacy from superluminal extensions is not quantum.

Speaker: Ms Amrapali Sen (International Centre for Theory of Quantum Technologies)

11:40 Superluminal tunneling times in relativistic QFT

Many recent experimental works involving quantum tunneling claim their observations are consistent with superluminal or instantaneous barrier traversal times. However, we have recently proved [1] that microcausality prevents superluminal dynamics in the presence of tunneling in a QFT framework in which a potential barrier is represented by a background field. In this talk I will discuss how one can nevertheless define tunneling times that can in certain situations can give rise to superluminal velocities. I will focus on two such situations. First I will look at group velocities defined by connecting the maxima of the density expectation value to the left and to the right of a potential barrier [2]. A second example will involve working with a position operator of the Newton-Wigner type. The density is then propagated by the sole positive energy sector – evading microcausality and leading to densities leaking from the light cone [3]. For each case I will discuss the underlying physics (which turns out to be very different) and draw some lessons. [1] M. Alkhateeb and A. Matzkin, Phys. Rev. D 112, 076005, 2025 [2] D. Sokolovski and A. Matzkin, in preparation (should be posted on arxiv by mid-April) [3] F. Daem and A. Matzkin, Phys. Rev. A 111, L060202, 2025

Speaker: Prof. Alex Matzkin (LPTM (CNRS and CY Cergy Paris Univ.))

12:00 → 14:00 Lunch Break

Options:

• Proviant Albano Restaurant, bar and café (House 2, floor 4). Buffet style with a la carte options at the cafe. Vegetarian and vegan options available.
• Restaurant Albanova (AlbaNova, floor 3 of the main building). Roslagstullsbacken 21. Three set menu options. Vegetarian options available.
• The Coffice Albano (Albano, house 3). Hannes Alfvéns väg 10. For pre-made options, as well as hot buffet and salad bar.
• Pressbyrån, Albano (Albano House 4) Albanovägen 12. For quick, pre-made sandwiches and salads to-go.

14:00 → 15:20 Experiment

Chair: Josh Foo

14:00 Measuring the speed of tunnelling particles

Although quantum tunnelling has been studied since the inception of quantum mechanics, some aspects remain controversial, particularly the duration of tunnelling events. In a recent experiment [1], we investigate the quantum-mechanical motion of particles in a system of two coupled waveguide potentials, where population transfer between the waveguides acts as a clock, enabling the measurement of particle speeds along the waveguide axis. Applying this approach to exponentially decaying states at a reflective potential step, we determine an energy–speed relationship for tunnelling particles. We find that the lower the particle energy, the higher the measured speed inside the potential step. Our findings contribute to the ongoing debate on tunnelling times and can also be interpreted as a test of Bohmian trajectories.

[1] V. Sharoglazova, M. Puplauskis, C. Mattschas, C. Toebes, J. Klaers, Nature 643, 67 (2025).

Speaker: Prof. Jan Klaers (University of Twente)

14:40 Coffee Break

15:20 → 17:00 Poster Session

15:25 Accessible Properties from the Perspectives of General Quantum Clocks

A central question in the study of quantum information theory in the presence of symmetries concerns which properties of a system can be inferred by observers without access to the laboratory frame. We show how using a quantum system as a reference frame allows one to evade symmetry constraints, focusing on systems that can serve as quantum clocks. However, realistic quantum clocks cannot perfectly keep track of time. This might suggest that they are operationally less useful than ideal clocks. In this work, we explore whether the opposite is possible: are there any features that arise in the non-ideal case that are absent in the ideal one, thereby rendering non-ideal clocks more advantageous? We investigate this question within the framework of quantum reference frames that generalizes the extra-particle approach. Overall, we characterize the perspectives of quantum clocks through their operational capabilities, such as performing state tomography of an invariant state using relational observables.

Speaker: Mr Apostolos Giovanakis (ETH Zurich)

15:25 Adding and removing subsystems in quantum reference frames

The tensor product rule for composing subsystems is central to information-theoretic formulations of Quantum Theory. Adopting a relational view, we describe the adding and removing of subsystems in a quantum reference frame (QRF) for finite discrete translations following E. Castro-Ruiz, O. Oreshkov (2025). We show that textbook compositional rules only hold in a QRF perspective if the reference system is compatible with a `classical' external state. This issue is closely related to the so-called paradox of the third particle. An initial frame perspective can be inconsistent with the existence of an extra system in some relative state, making information of potentially far away systems appear to affect locally the description relative to a frame. There is, however, a way to recover the tensor product rule for any QRF by an invariance-preserving unitary map on the setup, as long as if it is redefined to include the external observer. We show how this procedure induces a modified adding rule for subsystems with a physical interpretation. We make an analogy between the map applied to a quantum frame, which recovers the standard adding properties, and changes of coordinates in classical physics which, via the equivalence principle, make non-inertial frames appear inertial. The procedure also recovers transformations from inequivalent QRF approaches without projections, hinting at a conceptual framework where different formalisms are consistent at the same time.

Speaker: Ms Bruna Sahdo (IQOQI-Vienna)

15:25 Contextuality from the vacuum

Contextuality, a key resource for quantum advantage, describes systems in which the outcome of a measurement is not independent of other compatible measurements, in contrast to classical hidden-variable descriptions. We investigate the harvesting of contextuality from the vacuum of a quantum field using Unruh-DeWitt detectors. We show that localized interactions with the field can endow initially non-contextual detectors with contextuality with respect to Heisenberg-Weyl measurements, as quantified by contextual fraction. The harvested contextuality correlates with the emergence of Wigner function negativity, in agreement with known equivalences between these notions. Our results show that contextuality is a resource that can be extracted directly from the quantum vacuum and establish contextuality harvesting as a fundamental phenomenon in relativistic quantum information.

Speaker: Ms María Rosa Preciado-Rivas (University of Waterloo)

15:25 Creative Time and Temporal Openness in Spacetimes with Closed Timelike Curves

The nature of time and its genuine passage are central problems at the interface of physics and philosophy. Inspired by Nicolas Gisin’s argument that free will is essential for rational reasoning and therefore implies the reality of temporal passage, this study examines how the structure of time may be understood in universes admitting Closed Timelike Curves (CTCs), and what implications such scenarios may have for quantum indeterminism. Using conceptual analysis and thought experiments grounded in quantum theory and general relativity, I analyze how indeterministic quantum events interact with the idea of creative time – a conception of time in which genuinely new events come into being – in spacetimes containing CTCs. Particular attention is given to how the openness of both the future and the past might be understood from this perspective. The analysis identifies conditions under which Gisin’s account of real temporal becoming remains philosophically and physically consistent, while highlighting potential tensions between a creative conception of time and the possibility of time travel. Within this framework, the coherence of free will appears as a related question emerging from the underlying ontology of time. These considerations illuminate the interplay between temporal ontology, quantum theory, and the conceptual foundations of time in physics.

Speaker: Ms Nina Mazurewicz (University of Warsaw)

15:25 Emergence of Classicality in Wigner’s Friend Scenarios

The Wigner’s Friend thought experiment, where two observers disagree about experimental outcomes due to different models of measurements, has long been used to frame questions in quantum foundations. It has also recently seen a resurgence as a way to produce novel nonclassical effects such as the Local Friendliness Inequalities (LFIs). But few works have approached these topics using the powerful tools of decoherence theory. Here we study WF scenarios under quantum Darwinism, a framework that describes how environments store information about quantum systems during decoherence. We model the measurement thermodynamically: as a dynamical equilibration process between the system, the friend, and the environment that spreads information between them over time. We then observe how this model affects one’s ability to produce WF-type disagreements and violate LFIs. We find that in our model, the environment produces two novel WF-like effects, including a classical WF analogue. In addition, we numerically observe classicality emerging as the friend and environment grow in size. We also report on ongoing work to understand the relationship between temporal and spatial correlations in WF scenarios, by studying the connections between LFIs and Leggett-Garg inequalities. T. Rivlin, S. Engineer, V. Baumann, arXiv:2507.21221 (2025)

Speaker: Dr Tom Rivlin (TU Wien)

15:25 Entanglement dynamics in a curved spacetime

The interplay between quantum theory and gravity is still an open problem. Here, we investigate the dynamics of gravitationally induced entanglement in a single photonic state delocalized in a three-arms interferometer, each hosting quantum memories, in Earth's gravitational field. The output statistics can be related to entanglement measures, enabling the study of the dynamics of correlations induced between the internal and external degrees of freedom of the quantum system, after storage in different gravitational levels. Furthermore, in this setup we can also test fundamental postulates of quantum mechanics, such as Born rule, and we can perform Bell and Leggett-Garg tests in the presence of gravity.

Speaker: Mrs Marina Pisaturo (Universität Bremen)

15:25 Fully covariant Dirac equation

We detail how the Dirac equation can be expressed in the fully covariant relativistic quantum mechanics framework of the Geometric Event based quantum mechanics (GEB).

Speaker: Prof. Lorenzo Maccone (Università di Pavia, INFN Pavia)

15:25 Gravitational Interaction of Quantum Systems in the Weak-Field Regime

Understanding how quantum systems interact gravitationally remains an important open problem at the interface of quantum theory and general relativity. While a complete theory of quantum gravity is still lacking, valuable insight can be gained by studying quantum matter coupled to gravity in the weak field regime. In this work we investigate the gravitational interaction of quantum systems within the framework of linearized gravity. Attention is also given to situations in which the reference frame itself is associated with a quantum system. In this regard we explore how gravitational interactions are described when transformations between such frames are considered, and discuss the implications for frame-independent physical quantities.

Speaker: Mr Eleftherios Stamatelopoulos (University of Patras)

15:25 Machines for autonomous distinction (MADs) and distinguishability under constrained agency

How much memory does a quantum device need to tell two multi-time processes apart? We study process discrimination in a realistic regime where the probing device is reusable, time-homogeneous, and limited to finite coherent memory. While the strategy norm captures the ultimate power of arbitrary adaptive testers, it generally presumes step-dependent control and unbounded quantum memory. We introduce \emph{machines for autonomous distinction} (MADs), a class of fixed devices that probe a process step after step using the same quantum instrument, a coherent memory of dimension $d_a$, and a complete classical record for the final optimal decision. This defines a hierarchy of operational distinguishability measures. We prove that, for any finite horizon $N$, every admissible $N$-step tester can be compiled into a single MAD with an internal clock and sufficiently large memory, implying that the hierarchy increases with $d_a$ and reaches the strategy norm at fixed $N$. For stationary repeated-interaction processes, we further derive a one-step transfer-map description that generates co-emission probabilities for two simultaneous processes and bounds the optimal discrimination success probability. Simulations for a qubit model show explicitly how added coherent memory and internal time-keeping close the gap to fully general adaptive discrimination.

Speaker: Ms Magdalini Zonnios (Trinity College Dublin)

15:25 Relativistic spatiotemporal quantum reference frames from first principles

Existing approaches to relativistic quantum reference frames typically begin by assuming Lorentz or Poincaré symmetry and then constructing quantum frame transformations compatible with that structure. Here we propose an alternative route based on a minimal physical postulate: the existence of a perspective-invariant maximal velocity. Working within a timeless, constraint-based formulation in which spatial and temporal coordinates are treated as quantum observables, we introduce constraints that implement this requirement. We then analyze how the resulting constraint structure restricts the admissible transformations between spatiotemporal quantum reference frames. Observable coordinate time emerges relationally through conditional probabilities, connecting the construction to the Page-Wootters mechanism while extending it toward a relativistic spatiotemporal setting. Finally, we identify the conditions that such a framework must satisfy to recover full Lorentz covariance from the constraint structure alone.

Speaker: Dr Michael Suleymanov (Bar-Ilan University)

15:25 Scattering cross section formula derived from macroscopic detectors models

We are concerned with the justification of the statement, commonly (explicitly or implicitly) used in quantum scattering theory, that for a free non-relativistic quantum particle with initial wave function $\Psi_0(\mathbf{x})$, surrounded by detectors along a sphere of large radius $R$, the probability distribution of the detection time and place has asymptotic density (i.e., scattering cross section) $\sigma(\mathbf{x},t)= m^3 \hbar^{-3} R t^{-4} |\widehat{\Psi}_0(m\mathbf{x}/\hbar t)|^2$ with $\widehat{\Psi}_0$ the Fourier transform of $\Psi_0$. We give two derivations of this formula, based on different macroscopic models of the detection process. The first one consists of a negative imaginary potential of strength $\lambda>0$ in the detector volume (i.e., outside the sphere of radius $R$) in the limit $R\to\infty,\lambda\to 0, R\lambda\to \infty$. The second one consists of repeated nearly-projective measurements of (approximately) the observable $1_{|\mathbf{x}|>R}$ at times $\mathcal{T},2\mathcal{T},3\mathcal{T},\ldots$ in the limit $R\to\infty,\mathcal{T}\to\infty,\mathcal{T}/R\to 0$; this setup is similar to that of the quantum Zeno effect, except that there one considers $\mathcal{T}\to 0$ instead of $\mathcal{T}\to\infty$. We also provide a comparison to Bohmian mechanics: while in the absence of detectors, the arrival times and places of the Bohmian trajectories on the sphere of radius $R$ have asymptotic distribution density given by the same formula as $\sigma$, their deviation from the detection times and places is not necessarily small, although it is small compared to $R$, so the effect of the presence of detectors on the particle can be neglected in the far-field regime. We also cover the generalization to surfaces with non-spherical shape, to the case of $N$ non-interacting particles, to time-dependent surfaces, and to the Dirac equation.

Speaker: Ms Rashi Kaimal (University of Tübingen)

15:25 Stories in the two-state vector formalism

The two-state vector formalism is a time-symmetrised approach to quantum theory. Although its predictions can be derived from the principles of standard quantum mechanics, recent developments in constructing a covariant quantum field theory of particles with negative squared mass suggest that it may constitute a preferred interpretation. In our work, we identify an overlooked aspect of the formalism, which motivates the introduction of the concept of a story — a compatible pair consisting of a two-state vector and an ideal measurement. This notion carries fundamental physical significance within the formalism and provides a tool for examining the structure of the space of all two-state vectors. We analyze the problem of distinguishability and confirm that some pairs of two-state vectors or their statistical mixtures cannot be physically distinguished. This leads us to formulate the definition of a strictly non-separable two-state vector as a genuine manifestation of entanglement between the past and the future.

Speaker: Mr Patryk Michalski (University of Warsaw)

15:25 Temporal nonclassicality in continuous-time quantum walks

Understanding what makes a quantum process genuinely nonclassical in time is a central question in the foundations of quantum theory. We investigate this question in continuous-time quantum walks by comparing two operational notions of quantumness: a single-time measure based on the quantum–classical dynamical distance, and a multi-time quantifier based on violations of Kolmogorov consistency conditions for sequential measurements. We show that these notions are not equivalent: a quantum walk can reproduce the single-time probability distribution of a classical random walk while still exhibiting genuinely nonclassical temporal correlations. We further show that multi-time nonclassicality displays a universal short-time behavior determined by local connectivity, while at longer times it depends strongly on graph topology. Finally, we analyze the impact of decoherence in different bases, showing that distinct noise mechanisms affect temporal nonclassicality in qualitatively different ways. These results highlight continuous-time quantum walks as a natural setting in which to investigate the temporal structure of quantum processes.

Speaker: Mr Paolo Luppi (University of Milan)

15:25 The Impact of Universal QFT Effects in Observer-dependent Time Measurements

Vacuum fluctuations in quantum field theory impose fundamental limitations on our ability to measure time in short scales. To investigate the impact of universal quantum field theory effects on observer-dependent time measurements, we introduce a clock model based on the vacuum decay probability of a finite-sized quantum system. Using this model, we study a microscopic twin paradox scenario and find that, in the smallest scales, time is not only dependent on the trajectory connecting two events, but also on how vacuum fluctuations interact with the microscopic details of the clocks.

Speaker: Dr Rick Perche (Stockholm University)

15:45 Quantising causality

In generally covariant theories, physical configurations are defined modulo diffeomorphisms, and the induced equivalence relation is highly singular. In particular, recent results show that complete sets of observables need not be Borel-definable, and their existence may fail within standard measurable frameworks. This obstructs any direct parametrisation of spacetime geometry in terms of well-behaved invariants.

We adopt an operational formulation in which spacetime is specified by a measurable space of events, a probability measure, and a causal accessibility relation encoded by a measurable kernel. Physical equivalence is restricted to measure-preserving transformations. In this setting, the relevant invariant is the probability law obtained by sampling the kernel. By the reconstruction results of Gromov and Vershik, such matrix distributions provide complete invariants of measurable structures of this type, up to measure-preserving isomorphism. They therefore separate equivalence classes at the level of observable data, modulo null sets.

This leads to a state space of operational spacetimes realised as a subset of probability measures on infinite matrices. Within appropriate regularity classes, this space admits a natural structure as an infinite-dimensional manifold; in particular, it can be modelled as a Fréchet manifold when described in terms of smooth densities or moment coordinates. This provides a well-defined differential framework compatible with its statistical interpretation.

We propose to quantise causal structure on this space. The differential structure allows the construction of a cotangent bundle and, under suitable conditions, a canonical symplectic form. This yields a phase space for operational causal configurations. One can then construct a representation into a projective Hilbert space, thereby associating quantum states to classical causal data. In this representation, amplitudes encode invariant statistical features of causal relations.

This framework defines quantum causal states directly from operationally accessible structures. It bypasses the non-Borel-definability of observables in the fully diffeomorphism-invariant setting, while retaining the essential causal and measure-theoretic content of spacetime.

References:
Panagiotopoulos, A., Sparling, G. A. J., & Christodoulou, M. (2023). Incompleteness Theorems for Observables in General Relativity. PRL 131, 171402.
Vershik, A. M. (2004). Random metric spaces and universality. Russian Mathematical Surveys 59(2), 259–295.
Kuchař, K. V. (1992). Time and interpretations of quantum gravity. In Proceedings of the 4th Canadian Conference on General Relativity and Relativistic Astrophysics.

Speaker: Mr Nicolás Medina Sánchez (University of Vienna)

16:05 Analysis of the Precision of a Minimal Autonomous Quantum Clock

Quantum clocks, such as atomic clocks, are known to have advantages over classical ones. Autonomous quantum clocks are a relatively new addition to this realm. What makes them particularly interesting is the little external control they need. My research is focused on a minimal thermal clock model previously proposed. This consists of two qubits operating between macroscopic heat baths, extracting work from the heat flow and exerting it onto an external system, which works as a clock. I show that the precision of this particular model is classical and reproducible by stochastic models. I will also present results showing that the ladder system used as the clock evolves with non-Markovian dynamics. Finally, I will include a study of the clock in the virtual qubit framework.

Speaker: Mr Elia Sciama Bandel (University of Bristol)

Tuesday 26 May

09:00 → 12:00 Causality

09:00 Cyclic quantum causal models: the graph-separation problem and emergent time direction

Can the direction of time and causal structure be inferred from operational quantum principles, rather than assumed? Causal models and tensor networks both formulate a notion of quantum causality without reference to spacetime, in complementary ways. Causal models are operationally well-defined, yet typically assume acyclicity, which induces a global direction. Tensor networks assume no directionality, but their causal content is not operationally well understood. Connecting the two promises progress on both fronts. However a key challenge in the bridge is to consistently describe general quantum causal models beyond the acyclic case, allowing for cyclic scenarios where central causal modelling tools, such as graph-separation theorems breakdown.

This talk will first present a framework for cyclic quantum causal models equipped with a robust probability rule, and show how the graph-separation problem is resolved in this framework. We will then construct two-way mappings between such (possibly cyclic) quantum causal models and tensor networks, giving an operational meaning to causal influence in tensor networks by linking it to the concept of signalling between agents in causal models. Finally, the talk will discuss applications of these results for defining discrete space-time rotations of causal models that preserve signalling relations and some implications for the emergence of a time direction.

Based on joint works with Carla Ferradini, Victor Gitton and Giulia Mazzola (https://arxiv.org/abs/2502.04168, https://arxiv.org/abs/2603.12283).

Speaker: Dr V. Vilasini (Inria, Université Grenoble Alpes)

09:40 Identifying causal structures which cannot support quantum correlations without fine-tuning

Bell’s eponymous theorem implies that Quantum Mechanics is incompatible with local causality. This leads to tension between Relativity and Quantum Theory because certain quantum correla- tions cannot be explained locally. Non-classicality of such quantum correlations is often realized to arise because of their non-local nature. Making use of the framework of classical causality and causal discovery algorithms, Wood and Spekkens have shown that for the Bell causal structure Bell inequality violating correlations cannot be explained causally without resorting to fine-tuning. Here we follow Wood and Spekkens and use the framework of classical causality to study the non-classicality of observed correlations for other arbitrary causal structures. For our results we apply the IC∗ algorithm to observed conditional independences corresponding to certain causal structures and show that there are several other causal structures apart from the Bell structure which possess non-classical correlations that need not necessarily be non-local, but their causal explanation necessarily requires fine-tuning. We show that requiring fine-tuning to be explained classically is another interesting feature of the non-classicality of such correlations apart from just the fact that they could be non-local. Moreover, we show that the Bi-locality, the GHZ, and the general multi-partite Bell causal structures are also examples of such structures. On the other hand for a number of causal structures, which exhibit non-classical quantum correlations, we show that we can always explain such non-classical quantum correlations perfectly classically– using instead another causal structure which has the same observed conditional independences. The non-classicality of the observed correlations was an artifact of having assumed the wrong causal explanation. This work also validates the observation that causal discovery algorithms that try to reproduce a causal hypothesis for a given set of data must also look into properties of the data other than just the observed conditional independences present in it. A candidate for such a property can be the strength of correlations that are allowed to be possible. Since causal discovery finds applications in Machine Learning and Artificial Intelligence, our work may therefore be of relevance to these fields as well.

Speaker: Dr Shashaank Khanna (LIS, CNRS, Aix-Marseille University)

10:00 Higher-order processes beyond finite dimensional quantum theory

The framework of higher-order quantum operations (process matrices/supermaps) on finite-dimensional systems is primarily motivated by providing an information-theoretic abstraction of a spacetime environment. In doing so, it provides a way to extract operational causal structure from quantum circuit configurations, and a way to formalise quantum (indefinite) causal structures, which have been proposed as a salient information-theoretic feature of quantum gravity. However, there are strong reasons to push the theory of higher-order operations to infinite-dimensional and supra-quantum settings. Quantum gravity, when built on quantum field theory rather than quantum computation, is likely to involve infinite-dimensional quantum systems. And just as studying generalised theories places quantum theory along a spectrum of non-local correlations, studying higher-order processes on generalised theories places it along a spectrum of non-causal correlations. In this talk I will explain how abstract categorical methods give a way to develop these desirable generalisations via a theory-independent axiom for higher-order processes in terms of “locally-applicable transformations” [1], together with its application to infinite-dimensional systems in the unitary setting [2]. I will then describe recent results [3] giving a concrete representation of locally-applicable transformations for a broad class of theories—including classical theory, quantum theory, real quantum theory, and boxworld—revealing a surprising stability within the theory of higher-order processes beyond finite-dimensional quantum theory. The talk will emphasise the conceptual takeaways, and present the infinite-dimensional and supra-quantum cases in familiar linear-algebraic, functional-analytic, and circuit-diagrammatic terms, remaining accessible to those without prior exposure to category theory. [1] https://arxiv.org/abs/2205.09844 [2] https://arxiv.org/abs/2207.09180 [3] https://arxiv.org/abs/2602.23865

Speaker: Dr Matt Wilson (CentraleSupelec, University of Paris-Saclay)

10:20 Coffee Break

11:00 Exploring Sequential Identities within Indefinite Causal Structures

This talk investigates an interpretation of the quantum switch by projecting its spatial paths into a superpositional basis. By redefining traditional operations as delocalized superpositional processes, we explore whether indefinite causal order can be recast as a definite sequential evolution through superposed identities. We specifically consider configurations where a particle might undergo the same delocalized operation twice (e.g., A+iB→A+iB) or transition through an orthogonal pair (e.g., A+B→A−B), suggesting that causal ambiguity may be a basis-dependent perspective rather than an absolute one.

Speaker: Mr Stanislav Filatov (University of Latvia)

11:20 Closing the closed-labs loophole in device-independent tests of indefinite causality

Device-independent (DI) tests draw conclusions about nature solely from observed correlations, without trusting the devices used. Originating in Bell's work on nonlocality, this paradigm has become central to foundational studies of quantum theory and practical applications (e.g., cryptography). More recently, DI tests of indefinite causal order (ICO) have extended this approach to more exotic quantum structures where correlations may violate the assumption of a definite causal order. However, unlike Bell tests where loopholes can be closed, tests of ICO face a fundamental challenge that has been largely overlooked: the closed-labs (CL) assumption. This requires that each party interacts with a shared signal-mediating system at most once, preventing two-way signalling mimicking ICO correlations. Yet CL is inherently device-dependent and cannot be directly verified without revealing a definite spacetime structure, thereby destroying any causal indefiniteness present. In this talk, I introduce a framework that embeds a validation of the CL assumption directly within a DI test of ICO. By adding a minimal set of components, we transform CL from a trust assumption into an operationally testable feature of the lab infrastructure. Placing beamsplitters with detectors at the device input and output ports allows the inter-lab signalling structure to be probabilistically probed. The resulting detection statistics bound the number of system-device interactions per run, enabling an operational test of CL. Our work highlights a fundamental structural difference between DI tests of ICO and those of nonlocality: certifying ICO necessitates additional operational assumptions not required in the nonlocality setting. By making these assumptions explicit and testable, our framework shows that their associated limitations can be overcome. Our results enable rigorous certification of ICO suitable for practical applications such as cryptography, and open avenues for foundational experiments probing quantum causal structures, which may in turn offer insights for quantum gravity.

Speaker: Ms Hannah Seabrook (University of Bristol)

11:40 Higher-order quantum processes respecting closed labs in a spacetime have quantum controlled causal order

In quantum causality and quantum information, there is a vast landscape of abstract quantum protocols that permit cyclic or non-acyclic causal structures between quantum operations. This includes widely studied frameworks for indefinite causal order and higher-order quantum processes, such as process matrices. However, a longstanding open question has been which is the largest class of such abstract processes that admit physical realisations without post-selection. In this work, we provide a rigorous answer by adopting a top-down approach grounded in relativistic causality principles, motivated by the fact that physical experiments are implemented consistently with such principles in spacetimes with acyclic lightcone structures. Building on the framework of causal boxes, which characterise the most general quantum information-processing protocols compatible with fixed background spacetimes, we formalise additional physically motivated constraints (Acting Once + Local Order) capturing the closed-laboratory assumptions of the process matrix framework at a fine-grained spacetime level. We prove that any protocol realisable in a classical acyclic spacetime and satisfying these spatiotemporal closed-lab conditions is behaviourally equivalent to a quantum circuit with quantum control of causal orders (QC-QC), providing a top-down derivation of QC-QCs from physical principles. Our results therefore show that QC-QCs constitute precisely the class of higher-order quantum processes, including those with indefinite orders, that can be physically realised within classical spacetime, clearly ruling out the possibility of any experiment in this regime that could realise more general non-causal processes under such a closed-labs assumption. This clarifies the relationship between abstract higher-order process matrix frameworks and experimentally accessible quantum protocols, as well as the interplay between coarse-grained cyclic and fine-grained acyclic operational causal structures. We also develop characterisation techniques and results for process box protocols that lead to new causality-based open questions concerning spacetime quantum protocols and relativistic quantum experiments.

Speaker: Mr Matthias Salzger (International Centre for Theory of Quantum Technologies, University of Gdańsk)

12:00 → 14:00 Lunch Break

Options:

• Proviant Albano Restaurant, bar and café (House 2, floor 4). Buffet style with a la carte options at the cafe. Vegetarian and vegan options available.
• Restaurant Albanova (AlbaNova, floor 3 of the main building). Roslagstullsbacken 21. Three set menu options. Vegetarian options available.
• The Coffice Albano (Albano, house 3). Hannes Alfvéns väg 10. For pre-made options, as well as hot buffet and salad bar.
• Pressbyrån, Albano (Albano House 4) Albanovägen 12. For quick, pre-made sandwiches and salads to-go.

14:00 → 15:20 Philosophy

Chair: Gui Franzmann

14:00 Density Matrix Realism, Arrows of Time, and Observation Typicality

According to density matrix realism, the quantum state of the universe is objective but could be fundamentally mixed. I develop this framework and motivate it using considerations about the arrows of time. I then present a new class of results—observation typicality—which establish fundamental limits on our ability to infer or distinguish universal quantum states from observations. I explore how these epistemic constraints bear on the choice between density matrix realism and wave function realism.
(Related papers: https://arxiv.org/abs/2405.01025; https://arxiv.org/abs/2410.16860)

Speaker: Prof. Eddy Chen (University of California San Diego)

14:40 Coffee Break

15:20 → 16:00 Causality

15:20 A Causal-Modelling Reconstruction of Quantum Mechanics

Using Bayes' theorem and the quantum formalism, one can infer unobserved variables from observed variables in a quantum experiment [1]. Quantum mechanics specifies the physical relations among these variables. These relations can be expressed as a joint probability distribution which can then be factorized into a causal model. Based on [2-3] we propose a simple causal model in which the transformation between two sequential measurements is a collider for the hidden variables and observables associated with each measurement; conditioning on this collider induces a correlation between the measurements. This perspective helps explain why the model has been overlooked: it involves future-input dependence, in that the collider variable is an effect of variables in its future---the hidden variable and the observable associated with the second measurement. [1] Di Biagio, A., Donà, P., & Rovelli, C. (2021). The arrow of time in operational formulations of quantum theory. Quantum, 5, 520. [2] Price, H., & Wharton, K. (2021). Entanglement swapping and action at a distance. Foundations of Physics, 51(6), 105. [3] Price, H., & Wharton, K. (2025). Taming entanglement. arXiv preprint arXiv:2507.15128.

Speaker: Mr Joppe Widstam (Max Planck Institute for the Physics of Complex Systems)

15:40 Higher-order transformations of bidirectional quantum processes

Bidirectional devices are devices for which the roles of the input and output ports can be exchanged. Mathematically, these devices are described by bistochastic quantum channels, namely completely positive linear maps that are both trace-preserving and identity-preserving. Recently, it has been shown that bidirectional quantum devices can, in principle, be used in ways that are incompatible with a definite input-output direction, giving rise to a new phenomenon called input-output indefiniteness. Here we characterize the most general forms of input-output indefiniteness, associated with a hierarchy of higher-order transformations built from transformations of bistochastic quantum channels. Some levels of the hierarchy correspond to transformations that combine bistochastic channels in a definite causal order, while generally using each channel in an indefinite input-output direction. For other levels of the hierarchy, the indefiniteness can involve both the local input-output direction of each process and the global causal order among the processes. On the foundational side, the hierarchy of higher-order transformations characterized here can be regarded as the largest set of physical processes compatible with a time-symmetric variant of quantum theory, where the possible state transformations are restricted to bistochastic channels.

Speaker: Dr Kyrylo Simonov (University of Vienna)

17:00 → 18:30 Panel Discussion

18:30 → 21:30 BBQ

Wednesday 27 May

09:00 → 11:40 Quantum Reference Frames

09:00 Some observations concerning the role of unsharp time observables as quantum reference frames

The famous Pauli theorem rules out the possibility of time observables being represented by self-adjoint operators in physically realistic theories. Nevertheless, often time-translation covariant POVMs do exist. When used as quantum reference frames, such `non-ideality' is sometimes viewed as an inconvenience. In this talk, I will argue that in some settings it is an important feature - for instance regularising certain quantum field theories. It also opens up interesting new lines of investigation relating to e.g. the causal structure of QFTs, which I will describe.

Speaker: Prof. Leon Loveridge (University of South-Eastern Norway)

09:40 Foundations of scalar relational quantum field theory

We develop foundations for a relational approach to quantum field theory based on the operational quantum reference frames framework considered in a relativistic setting. Unlike other efforts in combining QFT with QRFs, we use the latter to provide novel mathematical and conceptual foundations for the former. We focus on scalar fields in Minkowski spacetime and discuss the emergence of relational local observables and fields from the consideration of Poincaré-covariant frame observables defined over the space of inertial reference frames. We recover a relational notion of Poincaré covariance, with transformations on the system directly linked to the state preparations of the QRF. We introduce and analyse various causality conditions, and construct an explicit example of a covariant scalar relational quantum field which is causal relative to operationally meaningful preparations of a relativistic QRF. The theory makes direct contact with established foundational approaches to QFT: we demonstrate that the vacuum expectation values derived within our framework reproduce many of the essential properties of Wightman functions, carry out a detailed comparison of the proposed formalism with Wightman QFT with the frame smearing functions describing the QRF's localisation uncertainty playing the role of the Wightmanian test functions, and show how the properties of algebras generated by relational local observables suitably extend the core axioms of Algebraic QFT.

Speaker: Mr Samuel Fedida (University of Cambridge)

10:00 Quantum limits of a space-time reference frame

We study the limitations for defining spatial and temporal intervals when the only available reference frame is a single composite quantum system, whose internal degrees of freedom serve as a temporal reference — a clock — and whose centre-of-mass degrees of freedom act as a spatial reference — a rod. By combining quantum speed limits with the mass–energy equivalence of special relativity, we show that spatial localisability and temporal resolution are not independent: sharpening one inevitably blurs the other. Specifically, the internal-energy coherence needed for precise timekeeping affects the centre-of-mass dynamics, enhancing position spreading during free evolution. As a result, a single composite system cannot act as a perfect quantum reference frame for both space and time, leading to a Heisenberg-like uncertainty relation between spatial and temporal intervals.

Speaker: Mr Davide Mattei (University of Rome, Tor Vergata)

10:20 Coffee Break

11:00 Time delocalization and causality across temporal quantum reference frames

In relational quantum dynamics, evolution emerges via the correlations between some system of interest and a clock system, which plays the role of a temporal reference frame. Their combined state satisfies a Wheeler-de Witt-like constraint equation, and therefore does not evolve, leading to a „block universe“ picture. I will talk about temporal localization and causal relations, when comparing emergent dynamics with respect to different choices of clock. Starting by explaining to which extent two clocks can agree on the direction of time and the temporal localization of events, I will then present ways to incorporate the operational notion of causality into relational dynamics. This requires a clearly defined notion of interventions, i.e. quantum operations, and I will compare two different approaches to modeling these operations within relational dynamics. The first considers their application via the choice of solutions to the constraint equation, i.e. the choice of which „history“ is considered. The second approach incorporates the operations into the constraint equation itself and thereby into its solutions, giving a dynamical picture of the interventions. From the perspective of a single clock, both approaches allow for a notion of operational causality in relational dynamics. However, for multiple clocks, only the second approach gives a consistent picture regarding causal relations, while necessarily manifesting some degree of temporal delocalization between frames. Moreover, this second approach, when considering certain cases of temporal delocalization, naturally describes scenarios with indefinite causal order, a well-known quantum feature of operational causality.

Speaker: Dr Veronika Baumann (IQOQI Vienna)

11:20 Network of quantum reference frames and the nature of conservation laws in quantum mechanics

In quantum theory, conservation laws are typically formulated at a statistical level, holding only on average across measurement outcomes. Recent work has shown that this limitation can be overcome in certain scenarios: by explicitly including the quantum reference frame associated with a system’s preparation, exact conservation can be recovered at the level of individual measurement outcomes. In this talk, we show that this picture becomes substantially more subtle in networks of quantum reference frames, where a single frame may prepare multiple other frames that, in turn, prepare systems which may subsequently interact. In such scenarios, tracking the exchange of conserved quantities in time reveals nontrivial and counterintuitive features, and raises questions about the very nature of conserved quantities.

Speaker: Dr Ismael Lucas de Paiva (Universidade Federal de Pernambuco)

11:40 → 12:00 Quantum Foundations

Chair: Leon Loveridge

11:40 The time of arrival problem in the Page-Wootters formalism

The time-of-arrival problem asks for a probability distribution for when a quantum particle reaches a specified location. It has been the subject of decades of debate, exemplifying the lack of a self-adjoint time observable in quantum theory. In the Page–Wootters framework, time is a relational quantity, emerging from correlations between a system and a clock induced by a global Hamiltonian constraint. We construct a time-of-arrival distribution by inverting the Page-Wootters approach, asking what time a clock reads given that the particle arrives at some fixed position. The result coincides with a common approach to the time-of-arrival problem, suggesting a potential relational interpretation to the latter. Our investigation provides a relational description of the time-of-arrival problem, applying the abstract Page-Wootters formalism to a concrete physical problem, and revealing some complications with the canonical interpretation of the Page-Wootters formalism as a theory of conditional probabilities.

(The manuscript corresponding to this abstract is in its final stages and will be uploaded to arXiv soon.)

Speaker: Ms Niyusha Hosseini (TU Wien)

12:00 → 14:00 Lunch Break

Options:

• Proviant Albano Restaurant, bar and café (House 2, floor 4). Buffet style with a la carte options at the cafe. Vegetarian and vegan options available.
• Restaurant Albanova (AlbaNova, floor 3 of the main building). Roslagstullsbacken 21. Three set menu options. Vegetarian options available.
• The Coffice Albano (Albano, house 3). Hannes Alfvéns väg 10. For pre-made options, as well as hot buffet and salad bar.
• Pressbyrån, Albano (Albano House 4) Albanovägen 12. For quick, pre-made sandwiches and salads to-go.

14:00 → 15:40 Quantum Foundations

Chair: Leon Loveridge

14:00 Exponential gain in clock precision using quantum correlated ticks

Creating precise timing devices at ultra-short time scales is not just an important technological challenge, but confronts us with foundational questions about timekeeping's ultimate precision limits. Research on clocks has either focused on long-term stability using an oscillator stabilized by a level transition, limiting precision at short timescales, or on making individual stochastic ticks as precise as possible. Here, we prove the viability of a conceptually different avenue: the autonomous self-correction of consecutive ticks by quantum correlations. This provides a new paradigm that integrates the advantages and insights from quantum transport theory to operate clocks at ultra-short timescales. We fully solve a model of coupled quantum systems and show how the emergent Pauli exclusion principle correlates the clock at the quantum level yielding an exponential advantage in precision. We furthermore demonstrate through simulations with realistic imperfections that this remarkable gain in precision remains stable providing a roadmap for implementation with contemporary quantum technologies.

Speaker: Mr Florian Meier (Technische Universität Wien)

14:20 Timed demolition measurements

Picture an experimental scenario where a closed quantum system, evolving through a time-independent Hamiltonian, is subject to a demolition measurement at a chosen time. The Hamiltonian, the measured observables, the initial state of the physical system and even its Hilbert space dimension are unknown; we nonetheless assume a promise or constraint on the energy distribution of the state. In this context we find that, for many natural energy constraints, the set of feasible time series or datasets can be characterized efficiently. Furthermore, under the assumption of a bounded energy spectrum, we prove that there exist "self-testing" datasets, whose approximate realization singles out specific Hamiltonians, states and measurement operators. Investigating to what extent the extrapolation of past measurement data is possible in this framework, we identify energy-constrained physical systems for which a non-trivial prediction at time $\tau$ requires a precision in the measurement data superexponential in $\tau$. We also discover two extrapolation phenomena: "aha! datasets", which drastically increase the predictability of the future statistics of an unrelated measurement; and "fog banks" fairly simple datasets that exhibit complete unpredictability at some future time $\tau$, but full predictability at a later time $\tau'>\tau$. Besides their relevance for quantum foundations, our results have applications in semi-device independent quantum communication, the simulation of complex quantum systems, and the design of optimal atomic clocks.

Speaker: Dr Miguel Navascués (IQOQI Vienna)

14:40 Quantum work operator beyond the two-point measurement scheme

In this paper we address and propose a solution to the problem of the definition of work in quantum mechanics. We define a work operator for driven quantum systems by recasting the problem in an automatized picture, where the driving of the system is replaced by a time-independent interaction with a battery. In this energy-conserving setting, the work operator is recovered as the energy that left the battery, thereby providing an operational definition of work that describes both classical and quantum statistics. Within this framework, the exchanged energy is not determined solely by the energy eigenvalues accessed by the two-point measurement scheme, but can also depend on off-diagonal coherences, which must therefore be included for a complete energetic description. We present an explicit protocol in which such coherence contributions are essential and a work operator is required to account fully for the energetics. We then derive a general quantum fluctuation theorem for this work operator, which recovers the Jarzynski equality as a special case in the appropriate classical regime. This also clarifies why our construction remains compatible with the previous no-go theorem for work fluctuations, since the relevant classical limit is more restrictive than mere diagonality in the initial energy basis. Our results thereby provide a framework for describing work and energy exchange in coherent quantum processes beyond the two-point measurement scheme, and open fascinating avenues for investigating the emergence of a quantum arrow of time.

Speaker: Mr Carlo Cepollaro (University of Vienna / IQOQI Vienna)

15:00 Coffee Break

18:00 → 18:30 Travel to Dinner

For information and directions, visit https://indico.fysik.su.se/event/9609/page/809-conference-dinner

18:30 → 21:00 Dinner

Thursday 28 May

09:00 → 11:00 Quantum Gravity

Chair: Sebastian Schuster

09:00 From Heat Engines to Cosmology

This talk raises several issues with standard explanations of time asymmetry, which assume a universally applicable statistical mechanical version of the second law of thermodynamics with a past hypothesis. The theme of criticism concerns the conceptual shifts which take place as thermodynamic entropy is reduced and the resulting definition (I focus on Boltzmann's) migrates between contexts. The most serious difficulties arise when attempting to use the past hypothesis to constrain explicit characterisations of the state of the early universe, while remaining consistent with modern cosmology. In particular, accounting for gravity, dark energy, infinite degrees of freedom, and observed inhomogeneities in the cosmic microwave background are all open problems, with varying prospects for satisfactory solution. I argue that this is enough to motivate considering alternative explanations of time asymmetry, and fortunately, some are available. I outline three options, finally making the case that Gryb and Sloan's ideas involving Janus points and attractors offer the most promising line of research in this area.

Speaker: Dr Lucy James (University of Bonn)

09:40 Coffee Break

10:20 Gravitational self-interaction mitigates superluminal signalling

The Schrödinger–Newton equation aims at describing the dynamics of massive quantum systems subject to the gravitational self-interaction. As a deterministic nonlinear quantum wave equation, it is generally believed to conflict with the relativistic no-signalling principle. Here I challenge this viewpoint and show that it is of a key importance to study the quantitative and operational character of the superluminal effects. To this end, a rigorous formalism of probability measures on spacetime was employed to quantify the probability of a successful superluminal bit transfer via the single-particle Schrödinger–Newton equation. Here it is demonstrated that such a quantity decreases with the increasing size and mass of the system. Furthermore, I prove that the Einstein–Dirac system, which yields the Schrödinger–Newton equation in the non-relativistic limit, is perfectly compatible with the relativistic causal structure. The presented study demonstrates that the Schrödinger–Newton equation, which is by construction non-relativistic, is in fact ‘more compatible’ with the no-signalling principle than the ordinary free Schrödinger equation.

Speaker: Mrs Julia Osęka-Lenart (Astronomical Observatory, Jagiellonian University)

10:40 Time dilation from entropy and purity

A quantum object is extended by virtue of uncertainty.  When subjected to gravity, different parts of its wave function experience distinct local relativistic effects, leading to tidal and interference phenomena absent in the classical limit. These effects can be incorporated into a geometric extension of classical spacetime. For states that are quantum correlated in at least two directions, a complete description of motion requires a non-Riemannian geometry whose form is controlled by the state's entropy and purity. A specific implication of this framework is the appearance of quantum parameters in the time-dilation law in addition to the usual dependence on velocity and gravitational potential. The new methods imply specific squeezing rates that optimize a quantum clock.

Speaker: Prof. Martin Bojowald (The Pennsylvania State University)

11:00 → 12:00 Closing Remarks