Abstract
Squeezed states of light are a valuable resource for reducing quantum noise in precision measurements. Injection of squeezed vacuum states has emerged as an important technique for reducing quantum shot noise, which is a fundamental limitation to the sensitivity of interferometric gravitational wave detectors. Realizing the most benefit from squeezed-state injection requires lowering optical losses and also minimizing squeezed quadrature fluctuations—or phase noise—to ensure that the large noise in the anti-squeezed quadrature does not contaminate the measurement quadrature. Here, we present an audio band squeezed vacuum source with 1.3−0.5+0.7 mrad of phase noise. This is a nearly tenfold improvement over previously reported measurements, improving prospects for squeezing enhancements in current and future gravitational wave detectors.
Highlights
The Advanced LIGO detectors recently ushered in the era of gravitational wave astronomy with their detection of a binary black hole merger [1]
Reducing quantum noise is essential for increasing the astrophysical reach of Advanced LIGO and the other advanced detectors under development [3,4], whose observation volume increases as the cube of the sensitivity improvement
While not part of the original Advanced LIGO design, squeezed vacuum injection has emerged in the last decade as an effective means of reducing quantum noise
Summary
OCIS codes: (270.6570) Squeezed states; (120.3180) Interferometry; (350.1270) Astronomy and astrophysics. The phase noise of the squeezed vacuum source used during the LIGO squeezing experiment [7] was primarily dominated by lock-point errors from detuning noise in the OPO cavity [16]. To stabilize the measurement quadrature, the LO is phase locked to the CLF by feeding back to a piezo on the LO path with a bandwidth of 10 kHz. A typical in-vacuum squeezing spectrum is presented, showing up to 6.5 dB of squeezing throughout the audio band. A measurement of the squeezed and anti-squeezed quadrature variances at one non-linear gain is insufficient to determine both the level of phase noise and the optical losses. A reduction in SHG length noise should be possible by switching to a well-designed
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