Exciton-Polariton Continuous Time Crystal with an Optomechanical Clock

Time crystals (TCs) broadly refer to the spontaneous breaking of time translation symmetry in quantum systems paralleling the similar concept of spatial symmetry breaking evidenced in crystalline matter. In this context, so-called discrete time crystals (DTCs) have been demonstrated in diverse physical systems including cold atoms, magnons in superfluid 3He, nuclear spins, photonic devices, and quantum computer qubits. DTC behavior is typically evidenced by the emergence of period doubling upon a time-dependent external perturbation. Very recently also continuous time crystals (CTCs) have been proposed in open quantum systems perturbed from their equilibrium with a time-independent drive [1]. We reveal, through both ultra-high resolution spectroscopy and time-resolved spatial first-order coherence function g(1)(r,t) experiments, that the exciton-polariton ground state in a trap can develop a non-linear self-sustained dynamics, intimately affected by mechanics in ways that expose characteristics of both CTCs and DTCs [2]. In contrast to other realizations, here the TC phases can be controlled by the power of the continuous-wave non-resonant optical excitation, and by the optomechanical interactions with phonons [3]. Non-Hermiticity, non-linearity, dissipative coupling between the polariton pseudo-spin states, and non-adiabatic coupling to a dynamical reservoir, are shown to be important ingredients for the observation of the spontaneous breaking of time-symmetry in such a many-body quantum system. Prospects for the realization of coupled polariton time-crystals, and their optomechanical control, will be also discussed.

[1] P. Kongkhambut et al, Science 377, 670 (2022). [2] I. Carraro-Haddad et al, Science 384, 995 (2024). [3] D. Chafatinos et al, Nature Communications 14, 3485 (2023).