Many-body Dynamics and Universality in Flatland

Project Information

UniFlat

Grant agreement ID: 101019302

DOI

10.3030/101019302

EC signature date 22 May 2021

Start date 1 November 2021

End date 31 July 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 425 898,00

EU contribution

€ 2 425 898,00

Coordinated by

THE CHANCELLOR MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom

Periodic Reporting for period 2 - UniFlat (Many-body Dynamics and Universality in Flatland)

Reporting period: 2023-05-01 to 2024-10-31

Summary of the context and overall objectives of the project

One of the great successes of the last-century physics was recognising that many complex and seemingly disparate many-particle systems are fundamentally alike. This allowed the classification of the equilibrium states of matter into universality classes, based on their basic properties such as symmetries and the form of the interparticle interactions. At the heart of this classification is the universal collective behaviour, insensitive to the microscopic details, displayed by systems close to phase transitions between the different states of matter.

A grand challenge for modern physics is to achieve such a feat for the far richer world of nonequilibrium collective phenomena. In recent years, theories that posit universal features of far-from-equilibrium many-body dynamics, common to systems as diverse as quantum magnets and the quark-gluon plasma, have been receiving support from experiments on the highly tuneable ultracold atomic gases, which are cooled to less than a millionth of a degree above absolute zero temperature.

The goal of this project is to make a leading contribution to this worldwide effort, through a series of coordinated experiments on homogeneous atomic gases, produced in `optical box traps'. In particular, in this project we are focusing on quantum gases in two-dimensional (2D) ‘Flatland’ geometry. We aim to study seemingly disparate non-equilibrium phenomena such as turbulence in driven gases and ordering dynamics in isolated quantum systems, and seek to identify the common universal principles that connect them.

Beyond academic interest, better understanding of turbulence is relevant for anything from weather prediction to understanding of the dynamics of financial markets, and better understanding of quantum systems far from equilibrium is essential for the emerging quantum technologies, with applications in areas such as quantum computing and sensing.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the first half of this project we have broadly worked on four fronts:

1. We used an existing setup for creation of 2D Bose gases to perform first experiments on both turbulence and ordering.

As originally envisioned, we have observed the key properties of the emergence and steady state of wave turbulence in 2D and also universal dynamics in the "coarsening" (ordering) of an initially far from equilibrium isolated 2D gas. Already going beyond the original plans, we have also observed an "inverse turbulent cascade" in a driven 2D gas, where the excitation are transported from small to large lengthscales, opposite to the usual "direct turbulent cascade".

2. We have been building a new superior 2D setup where these phenomena will be studied with unprecedented control and detection (high-resolution imaging).

This experiment is now producing 2D box-trapped condensates and should soon be producing new science.

3. Going beyond the original plans, we opened a new research direction (first on a separate 3D setup and then transposed to 2D) on driven disordered Bose gases, which turn out to also feature universal scaling dynamics.

4. Also going beyond the original plans, we opened another major new research direction, on transposing the ideas from equilibrium thermodynamics to far from equilibrium systems. As a milestone step in this direction, we experimentally constructed a universal equation of state for 3D wave turbulence.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the first half of the project we had 5 breakthroughs going beyond the state of the art, three of which are already published and two have recently been submitted for publication.

1. As originally proposed, we have observed the key properties of both the emergence ("birth") and the steady state ("life") of wave turbulence in driven 2D Bose gases (published in Galka et al., PRL 2022)

2. As originally proposed, we observed universal coarsening dynamics in a far-from-equilibrium 2D Bose gas (Gazo et al., arXiv:2312.09248 submitted for publication). In doing so, we have also introduced new analysis methodology that is relevant for all studies of universality far from equilibrium. This project simultaneously addressed two of our original plans, on the decay ("death") of turbulence and ordering of quenched Bose gases, showing that they are (as anticipated) fundamentally the same phenomena.

3. Going beyond the original proposal, we have demonstrated the possibility to capture the key properties of steady-state turbulence with a universal equation of state (Dogra et al., Nature 2023), akin to the succinct thermodynamic descriptions of the essence of equilibrium states of matter.

4. Going beyond the original proposal, we have experimentally uncovered and theoretically explained another example of universal far-from-equilibrium scaling dynamics, in driven and disordered noninteracting Bose gases, and started exploring the connection between this phenomenon and turbulence in interacting quantum gases (Martirosyan et al., PRL 2024).

5. Going beyond the original proposal, we have also observed an inverse turbulent cascade (from small to large lengthscales, akin to the butterfly effect) in a 2D Bose gas (Karailiev et al., arXiv:2405.01537 submitted for publication).

By the end of the project we expect to fulfil all the originally envisioned goals and additionally firmly establish two major new research directions, on the inverse turbulent cascades and the thermodynamics-like descriptions of far-from-equilibrium quantum matter.