Enhanced detection of a low-frequency signal by using broad squeezed light and a bichromatic local oscillator

Abstract

We experimentally study a protocol of using the broadband high-frequency squeezed vacuum to detect the low-frequency signal. In this scheme, the lower sideband field of the squeezed light carries the low-frequency modulation signal and the two strong coherent light fields are applied as the bichromatic local oscillator in the homodyne detection to measure the quantum entanglement of the upper and lower sideband for the broadband squeezed light. The power of one of local oscillators for detecting the upper sideband can be adjusted to optimize the conditional variance in the low frequency regime by subtracting the photocurrent of the upper sideband field of the squeezed light from that of the lower sideband field. By means of the quantum correlation of the upper and lower sideband for the broadband squeezed light, the low-frequency signal beyond the standard quantum limit is measured. This scheme is appropriate for enhancing sensitivity of low-frequency signal by the aid of the broad squeezed light, such as gravitational waves detection, and does not need to directly produce the low frequency squeezing in optical parametric process.

Broadband quantum noise reduction in future long baseline gravitational-wave detectors via EPR entanglement

“…This correlation allows us to reduce our uncertainty in â−θ by making a measurement on bθ . This key theoretical result that enables our conditional squeezing scheme has been realized experimentally recently [16].…”

Two-Carrier Scheme: Evading the 3 dB Quantum Penalty of Heterodyne Readout in Gravitational-Wave Detectors

“…In general, even though the signal field is on dark fringe, a bright LO is required for photon detection and can introduce audio-band scattering to the audio-band squeezer. We will show that, instead of observing audio-band squeezing [26,27] around LO frequency, radio frequency squeezing in a broadband two-mode quantum state is sufficient in our configuration, i.e., lowfrequency signals measurement with high-frequency squeezing [28,29]. Note that the audio-band noises with respect to the carriers cannot be omitted.…”

Demonstration of interferometer enhancement through Einstein–Podolsky–Rosen entanglement

“…The squeezed field ω S,I was mode-matched onto the linear cavity and the back-reflected light was separated with a Faraday rotator and a polarizing beamsplitter. We then performed bichromatic balanced homodyne detection 28 , 29 by overlapping the output field with two bright fields ω LO,I and ω LO,S at a 50:50 beam splitter and detecting the difference in photo current of the two outputs. In the bichromatic homodyne readout, electric fields at ω S ± Ω and ω I ± Ω are combined in such a way that the result directly gives the total quantum noise of the detection scheme.…”