Spontaneous coherence in spatially extended photonic systems: Non-Equilibrium Bose-Einstein condensation

Abstract

In this review, we give an interdisciplinary overview of Bose-Einstein condensation phenomena in photonic systems. We cover a wide range of systems, from lasers to photon condensates in dyefilled cavities, to excitons in semiconductor heterostructures, to microcavity polaritons, as well as emerging systems such as mode-locked lasers and classical light waves. Rather than diving into the specific properties of each system, our main focus will be to highlight those novel universal phenomena that stem from the driven-dissipative, non-equilibrium nature of these systems and affect the static, dynamic and coherence properties of the condensate. We conclude with our view on the future perspectives of this field for both fundamental science and technological applications.

Theory of coherent optical nonlinearities of intersubband transitions in semiconductor quantum wells

“…This is the typical condition under which important nonlinear effects such as optical bistability 37 or optical parametric oscillation start occurring 25 . The discussion that follows will mostly concentrate on the latter effect, which is a promising strategy to achieve lasing and Bose-Einstein condensation effects in novel wavelength regions 24,38 . Since the amplitude of the parametric coupling between the pump and the signal/idler modes is quantitatively related to the frequency shift, it is natural to characterize the parametric oscillation threshold in terms of the ratio between the frequency shift and the decay rate.…”

Vortex pair annihilation in arrays of photon cavities

“…Experimentally realized photon condensates are therefore drivendissipative systems. The availability of several other experimental platforms, such as exciton-polaritons [4], superconducting circuits [10] and Rydberg atoms [11], for the study of driven-dissipative systems and their interest for quantum simulation and quantum computation has spurred substantial theoretical activity [4,10,12,13].…”

“…These phenomena have been experimentally studied on a number of physical platforms such as superconductors, liquid helium and ultracold atoms [2]. What all these systems have in common is that they are up to a very good approximation in (local) thermal equilibrium, a condition that is typically broken in experimental platforms that are based on optical systems [3,4]. Optical Bose-Einstein condensates (BECs) have been experimentally achieved in optical cavities filled with a dye molecule solution and in microcavities where a photon is strongly coupled to an exciton resulting in excitonpolariton [5].…”

“…Experimentally realized photon condensates are therefore drivendissipative systems. The availability of several other experimental platforms, such as exciton-polaritons [4], superconducting circuits [10] and Rydberg atoms [11], for the study of driven-dissipative systems and their interest for quantum simulation and quantum computation has spurred substantial theoretical activity [4,10,12,13].A typical photon condensation experiment starts from an empty cavity and optical excitations are created by turning on the pumping laser where the phase transition is crossed when the photon density exceeds threshold. Upon crossing the threshold, the system goes from the disordered to the ordered state, which according to the KZ mechanism may lead to the formation of vortex pairs.…”

Enhanced Cavity Optomechanics with Quantum-well Exciton Polaritons

“…Polariton modes are spectrally separated from the exciton-induced absorption peak, enabling large optical quality factors, while their excitonic component is extremely sensitive to strain fields owing to the large GaAs deformation potential [37][38][39], thus prospecting strong optomechanical interactions. Polaritons are bosonic quasi-particles which can form nonequilibrium condensates [40][41][42], while strong excitonmediated nonlinearities enable the occurrence of superfluid behaviours [43,44], metastability [45,46] and parametric processes [47,48]. Optomechanical interactions offer an additional degree of freedom for quantum fluids of light foreshadowing new possibilities.…”