Observation of quantum depletion in a non-equilibrium exciton-polariton condensate
Observation of quantum depletion in a non-equilibrium exciton-polariton condensate
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DOI：
10.1038/s41467-019-14243-6
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发表时间：
2020-01-22
影响因子：
16.6
通讯作者：
Ostrovskaya, Elena A.
中科院分区：
文献类型：
--
作者：
Pieczarka, Maciej;Estrecho, Eliezer;Ostrovskaya, Elena A.
最早在液体He-4中发现的超流性与玻色-爱因斯坦凝聚(BEC)现象密切相关。然而，即使在零温度下，通过相互作用引起的涨落--量子耗尽现象，一部分量子液体也会从凝聚态中激发出来，进入更高的动量状态。原子BEC在热平衡下的量子耗尽在理论上得到了很好的理解，但很难测量。这种测量在驱动耗散激子-极化凝聚体中更具挑战性，因为它们的非平衡性质被预测为抑制量子耗尽。在这里，我们观察到高密度激子-极化子凝聚体的量子耗尽，通过检测由这一过程填充的基本激发的光谱分支。对这一激发分支的分析表明，激子-极化子凝聚体的量子耗尽可以紧跟或强烈偏离平衡Bogoliubov理论，这取决于激子极化子中的激子分数。我们的结果揭示了激子-极化子相互作用的超越平均场效应，并呼吁更深入地理解平衡和非平衡BEC之间的关系。平均场理论可以捕捉到极化子凝聚行为的许多方面，但相互作用会引入额外的量子效应。在这里，作者观察了驱动耗散凝聚体中的量子耗尽，并发现与平衡预测的偏差取决于激子分数。
Superfluidity, first discovered in liquid He-4, is closely related to Bose-Einstein condensation (BEC) phenomenon. However, even at zero temperature, a fraction of the quantum liquid is excited out of the condensate into higher momentum states via interaction-induced fluctuations-the phenomenon of quantum depletion. Quantum depletion of atomic BECs in thermal equilibrium is well understood theoretically but is difficult to measure. This measurement is even more challenging in driven-dissipative exciton-polariton condensates, since their non-equilibrium nature is predicted to suppress quantum depletion. Here, we observe quantum depletion of a high-density exciton-polariton condensate by detecting the spectral branch of elementary excitations populated by this process. Analysis of this excitation branch shows that quantum depletion of exciton-polariton condensates can closely follow or strongly deviate from the equilibrium Bogoliubov theory, depending on the exciton fraction in an exciton polariton. Our results reveal beyond mean-field effects of exciton-polariton interactions and call for a deeper understanding of the relationship between equilibrium and non-equilibrium BECs. Many aspects of polariton condensate behaviour can be captured by mean-field theories but interactions introduce additional quantum effects. Here the authors observe quantum depletion in a driven-dissipative condensate and find that deviations from equilibrium predictions depend on the excitonic fraction.