Abstract
We investigate the phase coupling between spatially separated polariton condensates under nonresonant optical pulsed excitation. In the simple case of two condensates, we observe phase locking either in symmetric or antisymmetric states. We demonstrate that the coupling symmetry depends both on the separation distance and outflow velocity from the condensates. We interpret the observations through stimulated relaxation of polaritons to the phase configuration with the highest occupation. We derive an analytic criterion for the phase locking of a pair-polariton condensate and extend it to polariton multiplets. In the case of three condensates, we predict theoretically and observe experimentally either in-phase locking or the appearance of phase winding with phase differences of between neighbors. The latter state corresponds to a vortex of winding number across the three polariton condensates.
- Received 19 December 2015
DOI:https://doi.org/10.1103/PhysRevX.6.031032
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Polaritons, quasiparticles that arise from strong coupling between light and matter, possess hybrid properties of photons and excitons. They combine the mobility and flexibility of light with the possibility of interactions due to their matter component. At high enough densities or low enough temperatures, polaritons can form a macroscopic coherent quantum state, a polariton condensate, or a polariton laser. Such a coherent state exhibits much of the same physics as Bose-Einstein condensation, as has been observed for cold atoms, but without requiring the ultralow temperatures necessary for atoms. Here, we investigate experimentally and theoretically the phase coupling between spatially separated polariton condensates at roughly 10 K.
Polariton condensates can be imprinted into any two-dimensional graph by spatial modulation of the pumping laser, offering the scalability matched only by optical lattices in ultracold atomic condensates. Here, we inject optically pumped polariton condensates into multisite configurations with arbitrary density profiles, which makes it possible to control the kinetics of the condensate at each site as well as the separation distance between any two neighboring sites. We explain the observations by the stimulated relaxation of polaritons to the phase configuration with the highest occupation across the lattice. We use interference patterns to study both polariton dyads and triads (i.e., two or three phase-locked condensates, respectively). In the case of a polariton triad, we surprisingly observe an exotic state of a lattice vortex in which the phase across the triad winds by .
We expect that our findings will pave the way for the realization of applications such as quantum polariton simulators, which are highly tunable systems that can emulate other not-so-easily-accessible quantum systems.