Light-Control of Nonequilibrium Quantum Matter

Project Information

CONQUER

Grant agreement ID: 101002955

DOI

10.3030/101002955

EC signature date 11 March 2021

Start date 1 September 2021

End date 28 February 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 994 183,00

EU contribution

€ 1 994 183,00

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 2 - CONQUER (Light-Control of Nonequilibrium Quantum Matter)

Reporting period: 2023-03-01 to 2024-08-31

Summary of the context and overall objectives of the project

The goal of controlling the properties of quantum materials and devices is a tantalizing one and motivates the research effort across different fields of Science. Traditional ways to control the properties
of a material include changing the temperature or the chemical composition to drive a phase transition. The use of light, either in the form ultra fast laser pulses or of cavity fields, is particularly appealing.
Recent experimental developments across fields such as ultra-fast science, condensed matter and quantum optics have turned the electromagnetic radiation from traditional spectroscopic probe into a powerful tool
to control and manipulate quantum materials and devices. Optical excitations have been shown to be able to drive a phase transition into an ordered phase (most notably superconductivity) at temperatures far
higher than the equilibrium one. Coupling a quantum material to the vacuum fluctuations of a cavity field has been recently shown to affect its spectral and transport properties.

The proposal sits at the rich interface between solid state physics and quantum optics and has therefore the potential of stimulating the development of a new generation of platforms,
such as non-linear photonic and optoelectronic devices based on strongly correlated materials, that supersedes what we have currently available.

The overall objectives as described in the description of the Action are two, namely (i) develop a theoretical framework to understand how to drive phase transitions (and in particular superconductivity) using classical light fields
and (ii) how to control the properties of a quantum material by means of coupling to a cavity field.

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

The research activity has been developed along the two pillars of the project, namely the light-control of non equilibrium quantum matter with classical and quantum light and has lead already to a number of important results.

On one hand we have started the investigation of strongly correlated electron systems driven by Markvovian environments. This is an important intermediate step to model light-induced phenomena in the solid-state where Floquet driving has to be balanced by dissipative mechanisms at play in solids, to avoid heating. In this context we have studied the dissipative dynamics of a superconductor in presence of pair losses. Our results have unveiled the universal dynamics of particle density and the decay in time of the superconducting order parameter which is remarkably different from the case of single particle losses. A second major result in this line of research has been the development of a new exact method to study the dynamics of dissipative quantum impurity models, based on a diagrammatic Monte Carlo (diagMC) sampling of the real-time perturbation theory in the impurity-bath coupling. This is a crucial intermediate step to develop a powerful Dynamical Mean-Field Theory approach to solve strongly driven and dissipative electronic systems.

In the context of quantum light-matter systems one of the main focus has been on the problem of Dicke superradiance in different settings: on one hand we investigated the case of electrons coupled to a non-uniform cavity mode and studied the associated electronic-superradiance transition. More recently we have studied the problem of energy transport in presence of collective light-matter effects. In particular we have shown the existence of a regime where energy current shows a super-linear scaling due to Dicke collective effects similar to super radiant behaviour. This regime can be experimentally achieved in circuit QED platforms. A new unanticipated research direction has emerged concerning the study of topological phases of matters in cavity quantum materials. In this context we have obtained a major result in one of the first theoretical investigation of this problem. Specifically we have demonstrated, in a paradigmatic model of topological material the Su-Schieffer-Heeger model, how by coupling to quantum light it is possible to control the topological properties of an electronic system and how signatures of a topological electronic transition appear in the spectrum of polariton modes.

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)

Our results have pushed the state of the art in two main respects. First, dissipative quantum impurity models are notoriously challenging to tackle and as such there are not many theoretical and computational tools available to solve them, especially
in the most interesting regime of strong correlation and strong driving. Our diagrammatic Monte Carlo approach, which is an exact method to study the dissipative dynamics of these models, represents in this sense a real progress. In the remaining part of the project we envision multiple applications of this technique and of related non-perturbative methods for dissipative impurity models to problems such as interacting quantum dots in monitoring/dissipative environments and as solvers for Dynamical Mean-Field Theory to study correlated electrons under drive and dissipation. Furthermore we will expand our activity on dynamics under light-irradiation using DMFT out of equilibrium, discussing questions related to thermalisation and the control of superconductivity by light. Another important progress beyond the state of the art is represented by our work on cavity control of topology. Traditioanally, much of the focus of the field of cavity control of quantum materials was in changing the phase diagram or driving the phase transition using cavity fields. It turned out that in single mode cavity problems this is not possible (a result that we also contributed in elucidating ). Our work highlighted the fact that however single mode cavity can have a tremendous impact on the topological properties of a material, which are usually defined for finite size systems (and contain non trivial edge modes). In the remaining part of the project we will continue explore these questions related to topology in cavity-electron systems
and extend our investigation to polaritonic platforms made out of strongly correlated excitations and the possible applications of them to novel lasing devices.