Abstract
We report on the cancellation of quantum back action noise in an optomechanical cavity. We perform two measurements of the displacement of the microresonator, one in reflection of the cavity, and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light in transmission of the optomechanical cavity allows us to cancel the back action noise between 1 kHz and 50 kHz, and obtain a more sensitive measurement of the microresonator's position. To confirm that the back action is eliminated, we measure the noise in the transmission signal as a function of circulating power. By splitting the transmitted light onto two photodetectors and cross correlating the two signals, we remove the contributon from shot noise and measure a quantum noise free thermal noise spectrum. Eliminating the effects of back action in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of back action in interferometric gravitational wave detectors such as Advanced LIGO.
Highlights
Over the past century, interferometers have been used to perform increasingly sensitive measurements for a wide variety of applications
As the power employed in advanced gravitational wave detectors is increased in order to reduce the impact of shot noise, the detectors are approaching the regime in which quantum backaction (QBA) begins to limit
The cavity orientation and feedback using the phase modulator (PM) for this measurement is shown in Fig. 2(b) and mimics that of the QBA measurement in Ref. [12]
Summary
Interferometers have been used to perform increasingly sensitive measurements for a wide variety of applications. We build upon the previous results and demonstrate a method of canceling the QBA in a tabletop interferometer that serves as a test bed for quantum noise reduction schemes for future gravitational wave detectors. Quadratures of the light to effectively cancel the QBA, resulting in a measurement limited only by shot noise [22], which would result in an increase in sensitivity below 100 Hz when applied to a detector such as Advanced LIGO. This cancellation must be done in a frequency-dependent way using an optical filter cavity. This reduction in displacement noise corresponds to an increase in the signal-to-noise ratio when compared to a displacement measurement where QBA is present
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