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

TL;DR

This paper demonstrates an experimental protocol using broadband high-frequency squeezed vacuum and bichromatic local oscillators to enhance low-frequency signal detection beyond the standard quantum limit, applicable to gravitational wave detection.

Contribution

It introduces a novel scheme employing broadband squeezed light and bichromatic local oscillators to improve low-frequency signal sensitivity without generating low-frequency squeezing directly.

Findings

Achieved measurement of low-frequency signals beyond the standard quantum limit.

Optimized conditional squeezing by adjusting local oscillator power.

Applicable to gravitational wave detection and other low-frequency measurements.

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 the local oscillators for detecting the upper sideband can be adjusted to optimize the conditional squeezing in the low frequency regime by subtracting the photocurrent of the upper sideband field of the squeezed light from that of the low 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 the low frequency signal by the aid of the broad squeezed light, such as gravitational waes detection, and does not need directly produce the low frequency squeezing in the optical parametric process.