## Scope

Quantum physics isn't as weird as you think. It's weirder. Recent years have witnessed a burgeoning development of quantum theory from its very foundation including quantum measurements, quantum decoherence, quantum nonlocality to technological applications, including quantum computing, quantum sensing, and quantum thermodynamics. The aim of this workshop is to bring together the researchers from the community of quantum physics to discuss recent advances on theory and experiments on quantum measurements and quantum control, with applications to quantum thermodynamics, quantum sensing and quantum computing.

This workshop takes place in the 3rd week **13th - 17th May 2024** of the WINQ program on Complex and Quantum Systems.

## Invited Speakers

Obinna Abah

Adolfo Del Campo

Paul Erker

Masahito Hayashi

Susana Huelga

Andrew Jordan

Peter Samuelsson

Augusto Smerzi

Yanhong Xiao

Alberto Imparato

## Schedule

You can download the program schedule in pdf format from here

Monday 13th | Tuesday 14th | Wednesday 15th | Thursday 16th | Friday 17th | |

9:30 - 10: 30 | Andrew N. Jordan | Augusto Smerzi | Susana Huelga | Masahito Hayashi | Peter Samuelsson |

10:30 - 11:00 | Fika | Fika | Fika | Fika | Fika |

11:00-12:00 | Adolfo Del Campo | Yanhong Xiao | Obinna Abah | Paul Erker | Alberto Imparato |

12:00 - | Lunch break and free discussions | Lunch break | Lunch break and free discussions | Lunch break and free discussions | Lunch break and free discussions |

13:15-14:30 | Andrew N. Jordan (Niels Bohr Colloquium at Auditorium 7, Hus 4) |

On Monday there will be an additional welcome to Nordita Fika at 3:00 PM at Nordita, floor 6. The workshop dinner will take place on 14th (Tuesday) at 5: 00 PM in restaurant Proviant Albano.

__Andrew Jordan: ____Nanoscale Quantum Devices__

__Andrew Jordan:__

__Nanoscale Quantum Devices__

*I will present the physics of nanoscale quantum devices. The focus of the talk will be on mesoscopic systems including quantum dots, contacts, wells, and superlattices, as well as superconducting systems, where I will discuss junction physics and quantum circuits. Applications of these devices for quantum transport, quantum thermodynamics and quantum information processing will be discussed.*

__Niels Bohr colloquim (Andrew Jordan): Quantum Measurement, The Book__

__Niels Bohr colloquim (Andrew Jordan): Quantum Measurement, The Book__

*I will present an overview of some of the most striking advances in the theory and experiments of quantum measurement. Topics covered will include weak measurement, continuous measurement, amplification, and how to break the cardinal rules of textbook quantum measurements.*

__Adolfo Del Campo: Quantum Dynamics in Krylov Space__

__Adolfo Del Campo: Quantum Dynamics in Krylov Space__

*The dynamics of quantum systems typically unfolds within a subspace of the state or operator space, known as the Krylov space. Krylov subspace methods provide a compact and computationally efficient description of quantum evolution, which is particularly useful for describing nonequilibrium phenomena of many-body systems with a large Hilbert space. In this talk, I will explore the notion of Krylov complexity as a probe for operator growth, quantum chaos, and scrambling. I will discuss the generalized quantum speed limits in Krylov space and the formulation of shortcuts to adiabaticity in Krylov space for quantum control and quantum optimization. *

__Augusto Smerzi: Entanglement Enhanced Phase Estimation Theory__

*Multipartite entanglement (ME) is a necessary resource for the development of a new generation of quantum technologies for sensing and quantum computation. However, the detection and characterization of ME is typically quite problematic because it requires the analysis of states living in pretty large Hilbert spaces. I will discuss a novel approach for the detection and characterization of multipartite entanglement based on the, so called, Fisher information. Specifically, I will demonstrate a profound connection between the ability to statistically differentiate quantum states and the class of entangled states essential for ultra-sensitive interferometry. I will finally discuss, as an application, multiphase estimation in the context of quantum distributed sensing.*

__Yanhong Xiao: Quantum metrology with entangled spins and squeezed light in atomic ensembles__

__Yanhong Xiao: Quantum metrology with entangled spins and squeezed light in atomic ensembles__

*Squeezing and entanglement play crucial roles in quantum metrology. However, achieving entanglement is challenging in systems with large atom number where higher absolute sensitivities are expected. I will review our experiment results on how to create squeezed atomic spin state for 10^11 atoms, and how to employ it for weak magnetic field sensing. In parallel, photon shot noise constitutes fundamental limits in optical measurements. The interplay of quantum optical noises and the sensing process will be discussed. I will show squeezed light can be self-generated during sensing to overcome the quantum limit, and simultaneous squeezing of the atomic spin and the light is possible for further suppression of quantum noises. Finally, prospects on routes to “quantum supremacy” in quantum metrology will be given.*

__Susana Huelga: Coherent Effects in Biological Processes: A Case Study in the Dynamics and Response of Open Quantum Systems__

__Susana Huelga: Coherent Effects in Biological Processes: A Case Study in the Dynamics and Response of Open Quantum Systems__

*The inquiry into non-trivial quantum effects in biological systems has persisted since the inception of quantum mechanics. Recent experiments utilizing non linear ultrafast spectroscopy of molecular aggregates have reignited this discussion. In this seminar, we will delve into recent research conducted within our group aimed at characterizing the possible origin and nature of coherent oscillations observed in the spectral response of pigment protein complexes (PPCs). These complexes serve as the fundamental components in light-induced reactions, crucial for processes ranging from photosynthesis to vision. We will explore the methodologies employed, which span from quantum master equations to tensor network simulations, to dissect the intricacies of PPC dynamics. This examination will highlight the significant challenges in establishing a quantitative connection between the experimental spectral response and underlying theoretical models. Furthermore, we will investigate the application of resource theories, rooted in the formalism of quantum information theory, to offer a complementary perspective on this enduring debate.*

__Obinna Abah: Quantum control in quantum technology__

*The recent research in quantum control has seen growing popularity of so-called “shortcuts to adiabaticity”, i.e., fast processes with the same outcome as an ideal, infinitely slow process. Although, various techniques of realising effective adiabatic dynamics are known, a critical assessment of the energetic resources required for their implementation is still lacking. In this talk, by considering some paradigmatic settings, I will assess the cost of implementing high fidelity control and provide a hierarchy in the resource intensiveness of quantum control. In the end I will present the applications of quantum control in the characterisation of quantum thermal machines and fast generation of nonclassical states.*

__Masahito Hayashi: Multiparameter quantum metrology through conic programming. From state-estimation to channel estimation__

*The ultimate precision in quantum sensing could be achieved using optimal quantum probe states. However, current quantum sensing protocols do not use probe states optimally. Indeed, the calculation of optimal probe states remains an outstanding challenge. In the first step, we present notable relation between the estimation precision and conic programming under correlated and uncorrelated measurement strategies even in the multiparameter setting. To calculate the estimation precision, we derive a conic program algorithm which minimizes a linear objective function subject to conic constraints on a operator-valued variable. In the second step, we study algorithms that efficiently calculate a probe state for correlated and uncorrelated measurement strategies. By using the conic program presented in the first step, our algorithm outputs a probe state that is a simple function of the optimal variable. We prove that our algorithm finds the optimal probe state for channel estimation problems, even in the multiparameter setting. For many noiseless quantum sensing problems, we prove the optimality of maximally entangled probe states. We also analyze the performance of 3D-field sensing using various probe states. Our work opens the door for a plethora of applications in quantum metrology.*

__Paul Erker: Clocks, Thermodynamics and Computation__

__Paul Erker: Clocks, Thermodynamics and Computation__

*The seminar will start with a discussion on why a single ion on its own does not constitute a clock. Once we know what does not constitute a clock, we will go on to find out about the minimal constituents of a clock. We need clocks to measure time as quantum mechanics does not provide us with an observable for it. To be able to understand and investigate time measuring devices, we introduce a model of a clock, namely the autonomous quantum clock and show how thermodynamics limits its abilities to keep time, as well as the trade-off relations that follow. Next we present an experiment that hints at the fundamental nature of these trade-off relations and also discuss the connection of timekeeping to quantum computation.*

__Peter Samuelsson: Measurement and control of nanoscale engines converting information to work.__

*I will present a discussion of nanoscale information-to-work engines, operating both in the classical and the quantum regime. The focus will be on how the operation of such machines can be understood and optimized by continuously monitoring the system state and using the obtained information to perform feedback. The engines that will be discussed are nanoscale implementations of Maxwell’s demon and Szilard’s engine, which are basic and conceptually clear examples of machines where information is converted to work. For concreteness I will discuss implementation of the engines in electronic nanoscale quantum dot systems and give examples of performed and possible experiments. The presentation will be centered around a number of my own contributions to the field.*

__Alberto Imparato: A quantum thermodynamics approach to optimization in complex systems__

*An optimization problem can be translated into physics language as the quest for the energy minimum of a complex system with a Hamiltonian that encodes the problem itself. Stretching the analogy further, the optimization problem can be seen as the controlled cooling of such a complex system so as it lands in a minimum of its complex energy landscape corresponding to the optimal solution of the given problem. I will introduce and discuss two methods for quantum cooling, and thus for optimization, entailing the use of quantum, non-Markovian baths connected to the system of interest. In the first method the bath is prepared in a suitable low energy initial state that efficiently cools down the system of interest. In the second method the bath is measured, and post-measurement excited states of the bath are selected, that correspond to low energy states for the system of interest.*

## Application/Registration

The joint application form for all four program workshops is found in the menu on the left under "Application" or at this link.

If you would like to participate, please register at this link by **Wed, 21 February 2024** (anywhere on Earth). In particular if you require accommodation, travel or visa support, it is critical that you apply by this deadline.

After this deadline review of applications will begin and results communicated within three weeks. Later applications are considered on a rolling basis, subject to remaining capacity.

__CAUTION! Occasionally scammers contact participants claiming to assist you with accommodation and travel arrangements etc. __

*Please be vigilant and do not share information with them! Also, please notify the organizers if you are in any doubt about the legitimacy of an approach, and never hesitate to contact us with any further questions.*

## Organisers

Sreenath K. Manikandan, Andrea Maiani, and Jing Yang