Exciton-polariton lasers are a promising source of coherent light for low-energy applications due to their low-threshold operation. However, a detailed experimental study of their spectral purity, which directly affects their coherence properties, is still missing. Here, we present a high-resolution spectroscopic investigation of the energy and linewidth of an exciton-polariton laser in the single-mode regime, which derives its coherent emission from an optically pumped and confined exciton-polariton condensate. We report an ultra-narrow linewidth of 56 MHz or 0.24 µeV, corresponding to a coherence time of 5.7 ns. The narrow linewidth is consistently achieved by using an exciton-polariton condensate with a high photonic content confined in an optically induced trap. Contrary to previous studies, we show that the excitonic reservoir created by the pump and responsible for creating the trap does not strongly affect the emission linewidth as long as the condensate is trapped and the pump power is well above the condensation (lasing) threshold. The long coherence time of the exciton-polariton system uncovered here opens up opportunities for manipulating its macroscopic quantum state, which is essential for applications in classical and quantum computing.

中文翻译：

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窄线宽激子偏振激光器


由于其低阈值操作，激子偏振激光器是用于低能量应用的有前途的相干光源。然而，仍然缺乏对其光谱纯度的详细实验研究，光谱纯度直接影响其相干特性。在这里，我们对单模状态下的激子-极化子激光器的能量和线宽进行了高分辨率光谱研究，该激光器从光泵浦和受限的激子-极化子凝聚体中获得相干发射。我们报告了 56 MHz 或 0.24 µeV 的超窄线宽，对应于 5.7 ns 的相干时间。通过使用限制在光诱导陷阱中的具有高光子含量的激子-极化子凝聚体来一致地实现窄线宽。与之前的研究相反，我们表明，只要冷凝物被捕获并且泵浦功率远高于冷凝（激光）阈值，由泵产生并负责产生陷阱的激子库不会强烈影响发射线宽。这里发现的激子-极化子系统的长相干时间为操纵其宏观量子态提供了机会，这对于经典和量子计算的应用至关重要。