# Beating the standard sensitivity-bandwidth limit of cavity-enhanced interferometers with internal squeezed-light generation

## TL;DR

This paper demonstrates that internal squeezed-light generation inside cavity-enhanced interferometers can surpass the standard sensitivity-bandwidth limit, significantly improving measurement capabilities for gravitational-wave detection and related applications.

## Contribution

It provides the first experimental validation that internal squeezing can enhance the sensitivity-bandwidth product beyond classical limits in interferometric sensors.

## Key findings

- Achieved a 36% increase in sensitivity-bandwidth product.
- First experimental demonstration of internal squeezing surpassing classical limits.
- Potential to develop advanced optomechanical force sensors.

## Abstract

The shot-noise limited peak sensitivity of cavity-enhanced interferometric measurement devices, such as gravitational-wave detectors, can be improved by increasing the cavity finesse, even when comparing fixed intra-cavity light powers. For a fixed light power inside the detector, this comes at the price of a proportional reduction in the detection bandwidth. High sensitivity over a large span of signal frequencies, however, is essential for astronomical observations. It is possible to overcome this standard sensitivity-bandwidth limit using non-classical correlations in the light field. Here, we investigate the internal squeezing approach, where the parametric amplification process creates a non-classical correlation directly inside the interferometer cavity. We analyse the limits of the approach theoretically, and measure 36% increase in the sensitivity-bandwidth product compared to the classical case. To our knowledge this is the first experimental demonstration of an improvement in the sensitivity-bandwidth product using internal squeezing, opening the way for a new class of optomechanical force sensing devices.