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Condensation of polaritons through optical confinement: increased coherence and reduced threshold

A. Askitopopulos, Hamid Ohadi, Z. Hatzopoulos, Pavlos G. Savvidis, Alexey Vitalievich Kavokin, Pavlos G. Lagoudakis

Published Jan 1, 2013• 0 citations
Publisher

Abstract

We report on a fully optically confined exciton-polariton condensate, spatially separated from the pump induced excitonic reservoir and analyze its formation process. The optically trapped condensate exhibits higher coherence features and an order of magnitude lower excitation density threshold with respect to previous excitation schemes as a result of the reduction of dephasing and depletion mechanisms associated with the interaction with the reservoir.

DOI
10.1364/cleo_si.2013.cm2m.5

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We investigate an optically trapped exciton-polariton condensate and observe temporal coherence beyond 1 ns in duration. Due to the reduction of the spatial overlap with the thermal reservoir of excitons, the coherence time of the trapped condensate is more than an order of magnitude longer than that of an untrapped condensate. This ultralong coherence enables high-precision spectroscopy of the trapped condensate, and we observe periodic beats of the field correlation function due to a fine energy splitting of two polarization modes of the condensate. Our results are important for realizing polariton simulators with spinor condensates in lattice potentials.
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Abstract In recent years, quantum information science has made significant progress, leading to a multitude of quantum protocols for the most diverse applications. States carrying resources such as quantum coherence are a key component for these protocols. In this study, we optimize the quantum coherence of a nonresonantly excited exciton-polariton condensate of long living polaritons by minimizing the condensate’s interaction with the surrounding reservoir of excitons and free carriers. By combining experimental phase space data with a displaced thermal state model, we observe how quantum coherence builds up as the system is driven above the condensation threshold. Our findings demonstrate that a spatial separation between the condensate and the reservoir enhances the state’s maximum quantum coherence directly beyond the threshold. These insights pave the way for integrating polariton systems into hybrid quantum devices and advancing applications in quantum technologies.
Bosonic condensates of exciton polaritons typically coexist and interact with an incoherent reservoir, which undermines measurements of key parameters of the condensate. Here, the authors overcome this limitation by creating a high-density polariton condensate in an optically induced box trap. In this interaction-dominated Thomas-Fermi regime, the condensate is fully separated from the reservoir, which enables a direct measurement of the polariton-polariton interaction strength. The results of the measurement are in agreement with theoretical predictions.
We report on the effect of decoherence on polariton bistability. The polariton hysteresis loop is shown to collapse in a similar way when increasing the temperature or under nonresonant excitation power. The hysteresis upward threshold is pulled to lower excitation power, whereas the downward threshold remains almost constant. This effect is explained by the population of an incoherent reservoir that induces dephasing and repulsive interaction that saturates at large densities. All experimental findings are accurately simulated with the excitonic Bloch equations and indicate that reservoir-induced dephasing can be dominant over the reservoir-induced energy blueshift.