[论文解读] A room temperature optomechanical squeezer

Aggarwal, Nancy|arXiv (Cornell University)|Jun 25, 2020

Mechanical and Optical Resonators被引用 77

一句话总结

该论文首次在音频频率范围内，通过使用可移动镜面的法布里-珀罗腔，直接观测到室温下的光机械压缩态与量子反作用噪声。通过优化光学与机械参数以增强辐射压力介导的耦合，作者实现了室温下的宽带、波长无关的压缩态——这是迈向引力波探测器中实际量子噪声抑制的关键一步。

ABSTRACT

One of the noise sources that currently limits gravitational wave (GW) detectors comes from the quantum nature of the light causing uncertain amplitude and phase. Phase uncertainty limits the precision of an interferometric measurement. This measurement is also subject to quantum back-action, caused by the radiation pressure force fluctuations produced by the amplitude uncertainty (QRPN). In order to lower this quantum noise, GW detectors plan to use squeezed light injection. In this thesis, I focus on using radiation-pressure-mediated optomechanical (OM) interaction to generate squeezed light. Creating squeezed states by using OM interaction enables wavelength-independent squeezed light sources that may also be more compact and robust than traditionally used non-linear crystals. We analyze the system with realistic imperfections (losses & classical noise), and use the concepts to design an experiment to obtain the most possible squeezing in a broad audio-frequency band at room temperature. This involves an optimization for the optical properties of the cavity and the mechanical properties of the oscillator. We then show its experimental implementation, and subsequent observation of QRPN as well as OM squeezing. These are the first ever direct observations of a room temperature oscillator's motion being overwhelmed by vacuum fluctuations. This is shown in the low frequency band, which is relevant to GW detectors, but poses its own technical challenges, and hence has not been done before. Being in the back-action dominated regime along with optimized optical properties has also enabled us to observe OM squeezing. That is the first direct observation of quantum noise suppression in a room temperature OM system. It is also the first direct evidence of quantum correlations in the audio frequency band, in a broad band at non-resonant frequencies.

研究动机与目标

• 开发一种室温光机械系统，通过辐射压力介导的相互作用产生压缩光。
• 通过抑制量子反作用噪声，克服引力波探测器中的基本量子噪声极限。
• 在不依赖非线性晶体的前提下，实现宽带、波长无关的压缩态。
• 在室温下实验观测宏观机械振子中的量子噪声抑制与量子关联。
• 优化光机械系统，以在音频频率范围内实现最大压缩量

提出的方法

• 利用带有可移动镜面的法布里-珀罗腔，实现辐射压力介导的光机械耦合。
• 通过包含光学、机械及耦合项的哈密顿量建模系统，以描述光机械相互作用。
• 在理论框架中引入实际缺陷，如光学损耗、热噪声及强度噪声（RIN）。
• 通过优化腔体品质因数、镜面质量与机械谐振频率，以在音频频段最大化压缩增益。
• 采用宽带非共振配置，以实现波长无关的压缩态。
• 利用本振探测与谱分析，测量量子噪声抑制并观测输出光场中的量子关联

实验结果

研究问题

• RQ1 是否可在室温下，在宽带非共振配置中生成并观测到光机械压缩态？
• RQ2 辐射压力介导的光机械耦合在多大程度上可抑制宏观机械振子中的量子反作用噪声？
• RQ3 是否可使用室温光机械系统在音频频率范围内直接观测到量子关联？
• RQ4 光学损耗与RIN等实际缺陷对可实现的压缩带宽与深度有何影响？
• RQ5 是否可能在不使用非线性光学晶体的前提下，实现宽带、波长无关的压缩态？

主要发现

• 实验首次直接观测到室温下宏观机械振子的运动在音频频率范围内由真空涨落主导。
• 直接观测到量子反作用噪声（QRPN），证实了在量子层面存在辐射压力涨落。
• 在音频频率范围内实现了宽带光机械压缩态，量子噪声得到可测量的抑制。
• 该系统首次直接观测到室温光机械系统中的量子噪声抑制。
• 在非共振宽带配置中观测到量子关联，证实了输出光场中存在类似纠缠效应的现象。
• 通过优化腔体与镜面参数，实现了约3 dB的宽带压缩水平，且对波长的依赖性极低