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Physical Review Letters

Stochastic Single-Shot Polarization Pinning of Polariton Condensate at High Temperatures

Y. C. Balas, E. S. Sedov, G. G. Paschos, Z. Hatzopoulos, H. Ohadi, Alexey Vitalievich Kavokin, Pavlos G. Savvidis

Published Mar 15, 2022• 8 citations
Publisher

Abstract

We resolve single-shot polariton condensate polarization dynamics, revealing a high degree of circular polarization persistent up to T=170 K. The statistical analysis of pulse-to-pulse polariton condensate polarization elucidates the stochastic nature of the polarization pinning process, which is strongly dependent on the pump laser intensity and polarization. Our experiments show that by spatial trapping and isolating condensates from their noisy environment it is possible to form strongly spin-polarized polariton condensates at high temperatures, offering a promising route to the realization of polariton spin lattices for quantum simulations.

DOI
10.1103/physrevlett.128.117401

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We demonstrate theoretically the spontaneous formation of a stochastic polarization in exciton-polariton Bose-Einstein condensates in planar microcavities under pulsed excitation. Below the threshold pumping intensity (dependent on the polariton lifetime), the average polarization degree is close to zero, while above threshold the condensate acquires a polarization described by a (pseudospin) vector with random orientation, in general. It is shown that the polariton-polariton interaction leads to suppression of the linear polarization degree of the condensate due to the self-induced Larmor precession of the pseudospin. We establish the link between the second-order coherence of the polariton condensate and the distribution function of its polarization. We examine also the mechanisms of polarization dephasing and relaxation.
The stability of spin of macroscopic quantum states to intrinsic noise is studied for non-resonantly-pumped optically-trapped polariton condensates. We demonstrate flipping between the two spin-polarised states with >10 4 slow-down of the flip rate by tuning the optical pump power. Individual spin flips faster than 50 ps are time resolved using single-shot streak camera imaging. We reproduce our results within a mean-field model accounting for cross-spin scattering between excitons and polaritons, yielding a ratio of cross- to co-spin scattering of ∼0.6, in contrast with previous literature suggestions.
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The spin and intensity of optically trapped polariton condensates are studied under steady-state elliptically polarized nonresonant pumping. Three distinct effects are observed: (1) spin inversion where condensation occurs in the opposite handedness from the pump, (2) spin and intensity hysteresis as the pump power is scanned, and (3) a sharp ``spin collapse'' transition in the condensate spin as a function of the pump ellipticity. We show these effects are strongly dependent on trap size and sample position and are linked to small counterintuitive energy differences between the condensate spin components. Our results, which fail to be fully described within the commonly used nonlinear equations for polariton condensates, show that a more accurate microscopic picture is needed to unify these phenomena in a two-dimensional condensate theory.