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Physics Seminar

Emergent quantum criticality in driven-dissipative cavity arrays

Speaker: Prof Vincenzo Savona (Ecole Polytechnique Federale de Lausanne)
Date: Wednesday 28 October 2020
Time: 15:00 in UK
Venue: Zoom

The possibility of realizing strongly correlated states in photonic cavity arrays has stimulated an intense research on open quantum many-body systems. One of the most intriguing phenomena is that of dissipative phase transitions. Due to the competition between the unitary dynamics and the dissipation into the environment, the non-equilibrium steady state of the open system can display a critical behavior, similarly to what happens for thermal or quantum phase transitions.

Here, I will present a theoretical study of the driven-dissipative Bose-Hubbard model in the presence of two-photon driving and losses, a model that is within reach of current experimental techniques based on circuit-QED resonators, and may be within reach of engineered optical systems. The mean-field analysis of the steady state of this system reveals the occurrence of a second-order phase transition, characterized by the spontaneous breaking of the Z2 symmetry of the model. The critical exponents associated to the transition are computed using a fully many-body approach, based on the corner-space renormalization method. These show that the phase transition belongs to the universality class of the quantum transverse Ising model, revealing thus the important role of quantum fluctuations and long-range entanglement at the critical point.

The present study indicates that nonlinear arrays of optical cavities, under appropriate conditions, may be suitable for the quantum simulation of a wide range of collective phenomena and condensed-matter models, among which the spin liquid phase in frustrated magnets.