NAQUAS: Non-equilibrium dynamics in Atomic systems for QUAntum Simulation

Lead Research Organisation: Newcastle University
Department Name: Sch of Maths, Statistics and Physics

Abstract

Recent progress in various areas of physics has demonstrated our ability to control quantum effects in customized systems and materials, thus paving the way for a promising future for quantum technologies. The emergence of such quantum devices, however, requires one to understand fundamental problems in non-equilibrium statistical physics, which can pave the way towards full control of quantum systems, thus reinforcing new applications and providing innovative perspectives. This project is dedicated to the study and the control of out-of-equilibrium properties of quantum many-body systems which are driven across phase transitions. Among several approaches, it will mainly focus on slow quenches and draw on the understanding delivered by the Kibble-Zurek (KZ) mechanism. This rather simple paradigm connects equilibrium with out-of-equilibrium properties and constitutes a benchmark for scaling hypothesis. It could pave the way towards tackling relevant open questions, which lie at the heart of our understanding of out-of-equilibrium dynamics and are key issues for operating in a robust way any quantum simulator. Starting from this motivation, we will test the limits of validity of the KZ dynamics by analyzing its predictions, thus clarifying its predictive power, and extend this paradigm to quantum critical systems with long-range interactions and to topological phase transitions. We will combine innovative theoretical ideas of condensed-matter physics, quantum optics, statistical physics and quantum information, with advanced experiments with ultracold atomic quantum gases. Quantum gases are a unique platform for providing model systems with the level of flexibility and control necessary for our ambitious goal. Their cleanness and their robustness to decoherence will greatly enhance the efficient interplay between theory and experiments, and provide a platform of studies whose outcomes are expected to have a strong scientific impact over a wide range of disciplines. On the short time scale we will exploit this knowledge to develop viable protocols for quantum simulators. In general, we expect that the results of this project will lay the ground for the development of the next generation of quantum devices and simulators.

Planned Impact

Our studies will contribute to develop a systematic understanding of non-equilibrium statistical mechanics, a truly interdisciplinary field of science relevant, to mention just a few, to biology and to the dynamics of financial markets. Specifically, our studies will complement and extend our understanding of the dynamical behavior of many-body systems at criticality. Indeed, a recent example taken from our own work is the observation of a turbulent cascade in a controlled setting of an ultracold gas which links and sheds light on the non-equilibrium dynamics and turbulence phenomena. We foresee that many such insights will be produced within our Consortium.

Our proposed work lies within the "Quantum Technologies" theme. More specifically, by providing a deeper understanding and direct control of out-of-equilibrium phenomena in quantum many-body systems, we will make impactful contributions to the areas of "Quantum simulation" and "Quantum metrology, sensing and imaging".

For example, by developing novel concepts and strategies, we will contribute to the development of robust and viable quantum simulators. On the basis of the insight we will gain on, we will also devise strategies and means to implement robust approaches, based on engineering the external potential, customizing the driving control fields, and tuning the interactions. Our final results will provide a relevant toolbox of knowledge and expertise for quantum technological applications.

This project will also have a large transformational impact on technology and society. A significant part of the requested funding is devoted to hire personnel (Postdocs, and in some non-UK nodes, also PhD students). Training high-level and highly motivated young researchers in world-leading international scientific teams collaborating across different European nodes is a crucial step for the success of the European-level Quantum technologies flagship, which is closely connected to the recently-founded UK Quantum Technology nodes. During our project we will give a robust formation to this new generation of "quantum engineers". They will become future industry leaders and policy-makers in the ever-more (quantum-)technology-driven world and they will spread their knowledge and training to the industrial community. For instance, the advanced numerical modelling skills or training in optics and electronics obtained by young scientists through this project are highly sought-after transferrable skills beyond academia. Examples of international companies that have hired our recent students and postdocs include Microsoft, Mathworks, Saint-Gobain, Areva, Safran, General Electric, Comsol, Motorola, etc. Our laboratories are also strongly connected to the emergence of high-technology start-ups that ensure the transfer of technology from the academic world towards society.

This work is also linked to quantum computing through (i) the need to control the time evolution of quantum systems which is central to quantum simulation and to quantum computing and (ii) the role of topology in quantum physics which leads to rich and complex many-body states accessible with quantum simulation and which paves the way to topologically protected quantum computing.

Publications

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Bland T (2020) Persistent current formation in double-ring geometries in Journal of Physics B: Atomic, Molecular and Optical Physics

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Comaron P (2019) Quench dynamics of an ultracold two-dimensional Bose gas in Physical Review A

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Liu I (2020) Kibble-Zurek dynamics in a trapped ultracold Bose gas in Physical Review Research

 
Description Phase transitions are ubiquitous in nature, describing the process by which a system changes its phase: perhaps the most familiar example is that of water turning into vapour, or ice; however, phase transitions are all around us, and play a key role into the formation of the Universe we live in today. A phase transition of increasing interest in the physical sciences corresponds to that in which a random system becomes ordered, in much the same way that a random collection of rowers synchronises under an excellent cox. This ordering happens suddenly, when the system reaches the appropriate "critical conditions" for the new collective behaviour to be favoured: it is such a process that renders a material, under the appropriate conditions and temperatures, to become magnetic, with all the "tiny magnetic spins" aligning themselves suddenly. Although details of the process by which this change of phase occurs depend on specific properties of the system, such as dimensionality, different physical systems can nonetheless exhibit the same behaviour at the critical transition point, a concept known as "universality". The past 3 decades have seen the emergence of a range of experimentally-generated systems with unprecedented control, enabling us to study the change of a system from "classical" (or random) to "quantum" (or "ordered"), in which all constituents of the system behave in exactly the same (collective) manner. Characterizing the non-equilibrium nature of such phase transitions is an open problem in condensed matter physics.

In this context, we have now performed detailed numerical analysis at an unprecedented scale to examine the short- and long-term dynamics of such a process across different physical systems, in the atomic and solid-state regimes. Both systems were found to exhibit same universal properties as the basic model of spins on a lattice of appropriate dimensionality (the so-called XY-model), with the observed differences between the systems being purely attributed to the distinct dimensionality of the system. The works, undertaken with leading international collaborators, shed important light into details of the processes, agreeing with experimental observations and providing crucial insight into timescales that cannot be currently probed experimentally.

In particular, working jointly with colleagues in Taiwan and Italy, we have modelled the emergence of "quantum order" from a random gas cooled to millionths of a degree above absolute zero, finding excellent agreement with the Trento experimental measurements. The specific system considered was a gas of ultracold atoms, the coolest material known to us anywhere in our Universe, suspended inside vacuum by lasers and magnets (Nobel prize in Physics 1997), which exhibits Bose-Einstein condensation, a phenomenon predicted in 1924 and observed in a clean way in 1995 (Nobel Prize in Physics 2001). The study considered such a system when driven gradually across the phase transition in a controlled manner, and revealed both intricate details of how "order" emerges from "randomness", and the fact that the duration of the quench plays a key role in the establishment of the quantum system. One aspect studied here was a mechanism known as "Kibble-Zurek", first raised by Tom Kibble in the cosmological context, and subsequently brought to the condensed-matter realm by Wojciech Zurek, which describes the spontaneous emergence of unconnected mini-regions of local order. The interplay of those so-called "defects" and the nonlinear dynamical evolution of the system create new interesting regimes of studying non-equilibrium processes in controlled quantum matter, and this study addressed the full re-equilibration process.
Exploitation Route Understanding about phase transitions, and learning how to perhaps control them, are key aspects of relevance to emerging quantum technologies. IN particular, envisaged quantum devices are likely to require an initially incoherent atomic cloud to be converted into a coherent Bose-Einstein condensate, before using it for precision measurements, Learning how to control this process, or how to optimise it, could have significant benefits in future envisaged atomtronic devices.
Sectors Aerospace, Defence and Marine,Education,Other

URL https://blogs.ncl.ac.uk/brettcherry/2018/09/20/visualising-how-matter-transforms-at-the-quantum-level/
 
Description Dynamics across a Josephson junction 
Organisation International School for Advanced Studies
Country Italy 
Sector Academic/University 
PI Contribution We studied the decay of superflow across a Josephson junction at both zero and finite temperatures, paying particular attention to the phase diagram and the generation of vortices. Excellent agreement with experimental findings was found, and our analysis helped further interpret various experimental findings.
Collaborator Contribution The group at LENS, Florence, Italy provided experimental data and particiapted in interpretation of our findings. The group at Trieste helped identify relevant parameter regimes to probe and to interpret obtained numerical data.
Impact Critical Transport and Vortex Dynamics in a Thin Atomic Josephson Junction K. Xhani, E. Neri, L. Galantucci, F. Scazza, A. Burchianti, K.-L. Lee, C. F. Barenghi, A. Trombettoni, M. Inguscio, M. Zaccanti, G. Roati, and N. P. Proukakis Phys. Rev. Lett. 124, 045301 - Published 31 January 2020
Start Year 2019
 
Description Dynamics across a Josephson junction 
Organisation University of Florence
Country Italy 
Sector Academic/University 
PI Contribution We studied the decay of superflow across a Josephson junction at both zero and finite temperatures, paying particular attention to the phase diagram and the generation of vortices. Excellent agreement with experimental findings was found, and our analysis helped further interpret various experimental findings.
Collaborator Contribution The group at LENS, Florence, Italy provided experimental data and particiapted in interpretation of our findings. The group at Trieste helped identify relevant parameter regimes to probe and to interpret obtained numerical data.
Impact Critical Transport and Vortex Dynamics in a Thin Atomic Josephson Junction K. Xhani, E. Neri, L. Galantucci, F. Scazza, A. Burchianti, K.-L. Lee, C. F. Barenghi, A. Trombettoni, M. Inguscio, M. Zaccanti, G. Roati, and N. P. Proukakis Phys. Rev. Lett. 124, 045301 - Published 31 January 2020
Start Year 2019
 
Description Equilibrium Phase Diagram & Dynamical Phase Transition Crossing / Kibble-Zurek Mechanism (3D Elongated BEC) 
Organisation Jagiellonian University
Country Poland 
Sector Academic/University 
PI Contribution We have undertaken detailed numerical studies of the equilibrium phase diagram of an elongated 3D Bose gas experiment done at Trento. We have studied questions of criticality at phase transition, and are currently studying dynamical delayed phase transition due to finite-duration quenches, in the context of Kibble-Zurek dynamics based on the stochastic Gross-Pitaevskii model.
Collaborator Contribution Partner Universities (Trento, Jagiellonian, Heidelberg) have contributed insights into interpretation of results and new suggestions on how to re-analyse some of the date for an enhanced interpretation and to demonstrate key relevant effects.
Impact Currently drafting manuscript for submission for publication
Start Year 2018
 
Description Equilibrium Phase Diagram & Dynamical Phase Transition Crossing / Kibble-Zurek Mechanism (3D Elongated BEC) 
Organisation University of Trento
Country Italy 
Sector Academic/University 
PI Contribution We have undertaken detailed numerical studies of the equilibrium phase diagram of an elongated 3D Bose gas experiment done at Trento. We have studied questions of criticality at phase transition, and are currently studying dynamical delayed phase transition due to finite-duration quenches, in the context of Kibble-Zurek dynamics based on the stochastic Gross-Pitaevskii model.
Collaborator Contribution Partner Universities (Trento, Jagiellonian, Heidelberg) have contributed insights into interpretation of results and new suggestions on how to re-analyse some of the date for an enhanced interpretation and to demonstrate key relevant effects.
Impact Currently drafting manuscript for submission for publication
Start Year 2018
 
Description Ultracold Quenches: 2D Study 
Organisation University of Trento
Country Italy 
Sector Academic/University 
PI Contribution We have been studying the long-term dynamics following instantaneous ultracold atomic quenches across the BKT phase transition. Most numerics has been done in-house, or through a Joint PhD student shared with Trento. We have found regimes of phase-ordering, and shown that the 1/t vortex number behaviour can also be seen in current experimental set-ups on Paris and Cambridge.
Collaborator Contribution PhD student who contributed to about half the numerics was shared with Trento University. The Trento PI (Prof. Dalfovo) also contributed through ideas and discussions.
Impact Quench dynamics of an ultracold two-dimensional Bose gas P. Comaron, F. Larcher, F. Dalfovo, and N. P. Proukakis Phys. Rev. A 100, 033618 - Published 27 September 2019
Start Year 2018