Abstract
A bosonic condensate of exciton polaritons in a semiconductor microcavity is a macroscopic quantum state subject to pumping and decay. The fundamental nature of this driven-dissipative condensate is still under debate. Here, we gain an insight into spontaneous condensation by imaging long-lifetime exciton polaritons in a high-quality inorganic microcavity in a single-shot optical excitation regime, without averaging over multiple condensate realisations. We demonstrate that condensation is strongly influenced by an incoherent reservoir and that the reservoir depletion, the so-called spatial hole burning, is critical for the transition to the ground state. Condensates of photon-like polaritons exhibit strong shot-to-shot fluctuations and density filamentation due to the effective self-focusing associated with the reservoir depletion. In contrast, condensates of exciton-like polaritons display smoother spatial density distributions and are second-order coherent. Our observations show that the single-shot measurements offer a unique opportunity to study fundamental properties of non-equilibrium condensation in the presence of a reservoir.
Highlights
Another difficulty in interpreting the experimental results lies in the strong influence of a reservoir of incoherent, highenergy excitonic quasiparticles on the condensation dynamics due to the spatial overlap between the reservoir and condensing polaritons
We use a wide range of detuning between the cavity photon and quantum wells (QWs) excitons[40] available in our experiments to vary the fraction of photon and exciton in a polariton quasiparticle[1,5], and demonstrate transition from a condensate of light, photonic polaritons with strong filamentation and large shot-to-shot density fluctuations to a more homogeneous state of heavy, excitonic polaritons with reduced density fluctuations, which is only weakly affected by the incoherent reservoir
The phonon-assisted and exciton-mediated relaxation of the injected free carriers[43] efficiently populates the available energy states of the lower polariton (LP) dispersion branch E(k), where k is the momentum in the plane of the QW
Summary
Another difficulty in interpreting the experimental results lies in the strong influence of a reservoir of incoherent, highenergy excitonic quasiparticles on the condensation dynamics due to the spatial overlap between the reservoir and condensing polaritons. Single-shot imaging performed on organic microcavities[33] provided evidence in support of earlier theoretical suggestions that the reservoir is responsible for dynamical instability and subsequent spatial fragmentation of the polariton condensate in a wide range of excitation regimes[34–37]. We confirm that spatial fragmentation (filamentation) of the condensate density is an inherent property of a non-equilibrium, spontaneous bosonic condensation resulting from initial random population of high-energy and momenta states, and will persist even after relaxation to the lowest energy and momentum occurs We unambiguously link this behaviour to the highly nonstationary nature of the condensate produced in a single-shot experiment, as well as to trapping of condensing polaritons in an effective random potential induced by spatially inhomogeneous depletion of the reservoir, i.e. the hole burning effect[34]. We use a wide range of detuning between the cavity photon and QW excitons[40] available in our experiments to vary the fraction of photon and exciton in a polariton quasiparticle[1,5], and demonstrate transition from a condensate of light, photonic polaritons with strong filamentation and large shot-to-shot density fluctuations to a more homogeneous state of heavy, excitonic polaritons with reduced density fluctuations, which is only weakly affected by the incoherent reservoir
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