Effecting spontaneous coherence in hybridised cavity-spin ensemble systems with incoherent driving

When the fermionic levels of spin-1/2 atoms are dipole-coupled to cavity photons which decay into the environment, energy losses are normally compensated by laser pumping. This work explores the consequence of weakening and removing the laser pump mechanism. We use Keldysh field theory [1] to study spontaneous coherence in a Tavis-Cummings system [2] (in the spirit of Bose-Einstein condensates) following incoherent driving from the decay bath. This novel approach presents opportunities to search for exotic nonequilibrium phase transitions, as well as building hybrid quantum structures using a superconducting resonator coupled strongly to crystalline impurity spin centres in diamond [3] to study quantum simulation. Our approach includes both coherent and incoherent photon dynamics from the decay bath. The Keldysh action would contain additional terms in the Dyson equation where only coherent photons are considered, and their effects would be seen in resulting phase diagrams.

References
[1] A. Kamenev, Field Theory of Non-Equilibrium Systems, Cambridge University Press (2011)
[2] M. H. Szymanska et al, Phys. Rev. B 75, 195331 (2007).
[3] D. I. Schuster et al, "High-Cooperativity Coupling of Electron-Spin Ensembles to Superconducting Cavities", Phys. Rev. Lett. 105, 140501 (2010).