Squeezed vacuum states enable optical measurements below the quantum limit and hence are a valuable resource for applications in quantum metrology and also quantum communication. However, most available sources require high pump powers in the milliwatt range and large setups that hinder real-world applications. Furthermore, degenerate operation of such systems presents a challenge. Here, we use a compact crystalline whispering gallery mode resonator made of lithium niobate as a degenerate parametric oscillator. We demonstrate about 1.4 dB noise reduction below the shot-noise level for only 300 μW of pump power in degenerate single-mode operation. Furthermore, we report a record pump threshold as low as 1.35 μW. Our results show that the whispering gallery-based approach presents a promising platform for a compact and efficient source for nonclassical light.

中文翻译：

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窃窃私语的画廊模式共振器压缩的真空状态

压缩的真空状态可以实现低于量子极限的光学测量，因此对于量子计量以及量子通信中的应用都是宝贵的资源。但是，大多数可用电源要求在毫瓦范围内具有较高的泵浦功率，并且需要较大的设置，这阻碍了实际应用。此外，这种系统的简并操作提出了挑战。在这里，我们使用由铌酸锂制成的紧凑型晶体耳语画廊模式谐振器作为简并参量振荡器。我们证明，在简并的单模运行中，仅对于300μW的泵浦功率，在散粒噪声以下可降低1.4 dB的噪声。此外，我们报告了创纪录的泵浦阈值低至1.35μW。