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Driven-dissipative systems

Quantum correlations in driven-dissipative systems

Can the interplay of interactions, drive and dissipation stabilize interesting phases of matter in quantum many-body systems? In particular, is it possible to stabilize interesting forms of quantum entanglement among the microscopic degrees of freedom? We investigate these questions in the context of exciton-polariton systems, which are experimentally studied at LKB in the team led by Alberto Bramati, and in collaboration with the experimental team of Maxime Richard at Majulam, in Singapore. Our main goal is to develop a simple but quantitative theoretical description of these systems, able to describe regimes where quantum correlations become detectable.

Exciton-polariton (EP) are hybrid light-matter quasiparticles which are created when a semiconductor microcavity is pumped with a laser. Inside of the of microcavity, EP quasiparticles interact via their matter component (namely, electron-hole pairs subject to both Coulomb interaction and Pauli exclusion), and can be detected optically via the losses of photons through the mirrors forming the cavity. Interactions among EP create the analogous of quantum gases or fluids, but fundamentally differ from cold atoms (as also studied extensively at LKB) in that they are intrinsically out-of-equilibrium degrees of freedom which exist only thanks to the pump laser (with a lifetime in the pico- to nanosecond scale). This raises new fundamental questions regarding the structure of entanglement in these systems; and this structure can manifest itself in the quantum correlation among the photons leaving the cavity.

On the theoretical level, we develop a quantitative understanding of EP systems and of the outgoing light field via an effective description based on the so-called Bogoliubov theory, originally developed in the context of low-energy quantum fluids. This approach has allowed us to uncover fundamental properties of EP systems which had hitherto been overlooks, such as the key role played by the thermal phonons of the solid state lattice embedding the EP system, a result recently published in Physical Review X. Hand in hand with our experimental colleagues both at LKB and inSingapore, we are currently trying to predict the nature of the correlations among the outgoing photons, and to identify regimes where quantum-entangled pairs are potentially produced.

Periodically-kicked quantum gases

A past activity of team was focused on the quantum dynamics of periodically-kicked atoms, a system called the quantum kicked rotor, where the phenomenon of dynamical localization takes place. In this context, several fundamental problems have been explored, such as coherent back [Hainaut et al., Phys. Rev. Lett. 118, 184101 (2017)] and forward [Hainaut et al., Nature Com. 9, 1382 (2018)] scattering effects , analogous to those encountered in disordered systems, or the multifractal nature of wave functions at the onset of the Anderson transition in the quasi-periodic version of the quantum kicked rotor [P. Akridas-Morel, Phys. Rev. A 100, 043612 (2019)]. These activities have been especially led by Dominique Delande, Nicolas Cherroret and the Quantum Systems group in Lille.
In more recent works, we have explored other types of periodically-driven systems where, in particular, particle interactions are involved. Among them, the nonlinear quantum kicked rotor in the low energy regime, a system where we have identified a long-lived phenomenon of prethermalization [Martinez et al., Phys. Rev. A 106, 043304 (2022)]. Recently we have also studied the quantum dynamics of Bose gases subjected to periodically-kicked interactions [Duval et al., Phys. Rev. A 105, 033309 (2022)]. In this system, the wave function was previously shown to exhibit a fast exponential spreading in momentum space in the limit of infinitely short kicks. By revisiting this problem for kicks or arbitrary duration, we have on the contrary shown that the spreading is not exponential but rather subdiffusive at long time.

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