Abstract
Photon blockade is the result of the interplay between the quantized nature of light and strong optical nonlinearities, whereby strong photon-photon repulsion prevents a quantum optical system from absorbing multiple photons. We theoretically study a single atom coupled to the light field, described by the resonantly driven Jaynes--Cummings model, in which case the photon blockade breaks down in a second order phase transition at a critical drive strength. We show that this transition is associated to the spontaneous breaking of an anti-unitary PT-symmetry. Within a semiclassical approximation we calculate the expectation values of observables in the steady state. We then move beyond the semiclassical approximation and approach the critical point from the disordered (blockaded) phase by reducing the Lindblad quantum master equation to a classical rate equation that we solve. The width of the steady-state distribution in Fock space is found to diverge as we approach the critical point with a simple power-law, allowing us to calculate the critical scaling of steady state observables without invoking mean-field theory. We propose a simple physical toy model for biased diffusion in the space of occupation numbers, which captures the universal properties of the steady state. We list several experimental platforms where this phenomenon may be observed.
Highlights
Thermal equilibrium is an incredibly powerful and constraining property of a large class of quantum many-body systems
Quantum systems departing from equilibrium often exhibit rich novel physics, including phenomena such as many-body localization [1,2,3], many-body scars [4,5], time-crystalline order [6,7,8,9,10,11,12], exotic Floquet order [13,14,15,16,17], dynamical phase transitions [18], and superradiance [19,20,21]
III we present a semiclassical treatment of the problem and a brief description of the physical intuition behind the critical point
Summary
Thermal equilibrium is an incredibly powerful and constraining property of a large class of quantum many-body systems. Processes of interest often involve strong (coherent) driving, e.g., by lasers, in part to overcome the losses due to the fact that the system of interest is typically coupled to a highly incoherent environment This combination of strong driving and incoherent loss processes often results in a quantum system which is far from thermal equilibrium. This implies that the driven oscillator can effectively tunnel off to a high-photon-number state, for which the nonlinearity is less important It appears that the breakdown of the photon blockade proceeds via a continuous dissipative phase transition [21,48,57,59,75]. More technical aspects of the analysis are presented in the Appendices
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