AI 中文总结
该研究提出循环正交腔内信号放大技术，利用失谐信号再循环腔内的OPA作为相位敏感放大器，可在宽频率范围提升引力波探测器的量子噪声极限灵敏度。
AI 中文摘要
激光干涉引力波探测器的高频灵敏度受限于量子散粒噪声。提高腔内循环光功率可降低散粒噪声，但受热效应和光机械不稳定性的约束。我们提出循环正交腔内信号放大技术，其中失谐信号再循环腔内的光学参量放大器（OPA）被用作引力波信号正交分量的相位敏感放大器。通过将信号再循环腔失谐π/4，光学正交分量在每次往返时旋转π/2，因此在相位正交中产生的信号仅在经过OPA的奇数个往返后才出现在读出相位正交中。读出相位正交中由两次往返分隔的连续贡献具有交替符号，使得这种两次往返演化呈反谐振状态。然而，在每个两次往返周期内，同一光场经历一次放大和一次衰减，因此真空压缩和参量增益均不累积。尽管两次往返分隔的信号贡献之间存在相消干涉，但OPA提高了通过输出耦合器提取的信号分量，从而提升了信噪比。当OPA增益足够大时，响应趋近于具有有效功率增强1/τ²的干涉仪，其中τ是构成放大器腔的正交旋转镜的振幅透射率。我们将该方案应用于当前一款计划近期升级的引力波探测器，结果显示其在延伸至千赫兹波段的宽频率范围内提升了量子噪声极限灵敏度。
英文摘要
The high-frequency sensitivity of laser-interferometric gravitational-wave detectors is limited by quantum shot noise. Increasing the circulating optical power reduces shot noise, but is constrained by thermal effects and optomechanical instabilities. We propose cyclic-quadrature intracavity signal amplification, in which an optical parametric amplifier (OPA) inside a detuned signal-recycling cavity is used as a phase-sensitive amplifier of the gravitational-wave signal quadrature. By detuning the signal-recycling cavity for $π$/4, the optical quadratures rotate by $π$/2 on each round trip, so a signal generated in the phase quadrature appears in the readout phase quadrature only after odd-numbered passes through the OPA. Successive contributions to the readout phase quadrature, which are separated by two round trips, have alternating signs, making this two-round-trip evolution anti-resonant. During each two-round-trip cycle, however, the same field experiences one amplification and one deamplification, so neither vacuum squeezing nor parametric gain accumulates. Despite the destructive interference between signal contributions separated by two round trips, the OPA increases the signal component extracted through the output coupler, thereby improving the signal-to-noise ratio. When the OPA gain is sufficiently large, the response approaches that of an interferometer with an effective power enhancement of $1/τ^2$, where $τ$ is the amplitude transmissivity of the quadrature-rotation mirror that forms the amplifier cavity. We apply the proposed scheme to a current gravitational-wave detector with a near-future upgrade and show that it improves the quantum-noise-limited sensitivity over a broad frequency range extending into the kilohertz band.
