Developing spontaneous coherence in incoherently-driven Tavis Cummings system

This work examines the possibility of developing spontaneous coherence in a driven-dissipative hybrid quantum system composed of a superconducting resonator coupled to a solid-state spins ensemble. Previous theoretical studies, involving microcavity polaritons for example, use an effective fermionic pump to generate the collective coherence and condensation of the quasi-particles. Instead of a phenomenological approach, this work develops a microscopic theory by means of a nonequilibrium cavity system with the addition of an incoherent bosonic (optical) pump. This prompts the use of Schwinger-Keldysh technique to analyse the system dynamics. The optical driving mechanism is equivalent to adding non-Markovian noise to the cavity, which causes an effective spin-spin interaction mediated by photons. Most importantly, this mechanism is present on the mean-field level. The form of its distribution function has a strong effect on the condensation behaviour which is shown in various phase diagrams that compare the cavity system with and with without the optical drive. For specific ranges of the fermionic pump strength (a mathematical construct that does not exist in the hybrid system), the phase diagrams show novel exotic behaviour that may be caused by the effective spin-spin interactions. It is plausible that the optical driving can develop spontaneous coherence in the cavity, but this is still inconclusive and needs to be studied further. Although these nonequilibrium quantum optics systems potentially find use in quantum information processing as quantum memories, they may also double as a quantum simulator, allowing further exploration into the nonequilibrium phase transitions of solid-state devices