According to quantum measurement theory, "speed meters" -- devices thatmeasure the momentum, or speed, of free test masses -- are immune to thestandard quantum limit (SQL). It is shown that a Sagnac-interferometergravitational-wave detector is a speed meter and therefore in principle it canbeat the SQL by large amounts over a wide band of frequencies. It is shown,further, that, when one ignores optical losses, a signal-recycled Sagnacinterferometer with Fabry-Perot arm cavities has precisely the sameperformance, for the same circulating light power, as the Michelson speed-meterinterferometer recently invented and studied by P. Purdue and the author. Theinfluence of optical losses is not studied, but it is plausible that they befairly unimportant for the Sagnac, as for other speed meters. With squeezedvacuum (squeeze factor $e^{-2R} = 0.1$) injected into its dark port, therecycled Sagnac can beat the SQL by a factor $ \sqrt{10} \simeq 3$ over thefrequency band $10 {\rm Hz} \alt f \alt 150 {\rm Hz}$ using the samecirculating power $I_c\sim 820$ kW as is used by the (quantum limited)second-generation Advanced LIGO interferometers -- if other noise sources aremade sufficiently small. It is concluded that the Sagnac optical configuration,with signal recycling and squeezed-vacuum injection, is an attractive candidatefor third-generation interferometric gravitational-wave detectors (LIGO-III andEURO).
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机译：根据量子测量理论，“速度计”（用于测量自由测试质量的动量或速度的设备）不受标准量子限制（SQL）的影响。结果表明，萨格纳克干涉仪重力波检测器是一种速度计，因此原则上它可以在很宽的频率范围内对SQL进行大量击败。进一步显示，当人们忽略光损耗时，具有法布里-珀罗臂腔的信号回收Sagnac干涉仪在相同的循环光功率下具有与P最近发明和研究的迈克尔逊速度计干涉仪完全相同的性能。普渡大学和作者。光学损耗的影响尚未研究，但对于Sagnac而言，与其他测速仪相比，光学损耗的重要性不大。将svacezedvacuum（压缩因子$ e ^ {-2R} = 0.1 $）注入其暗端口后，循环使用的Sagnac可以在$ 10 {\ rm Hz}频带上以$ \ sqrt {10} \ simeq 3 $击败SQL。 \ alt f \ alt 150 {\ rm Hz} $，使用（量子受限的）第二代高级LIGO干涉仪所使用的相同的循环功率$ I_c \ sim 820 $ kW-如果其他噪声源足够小。结论是，具有信号再循环和压缩真空注入功能的Sagnac光学配置是第三代干涉式重力波检测器（LIGO-III和EURO）的有吸引力的候选者。
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