# A new type of quantum speed meter interferometer: measuring speed to search for intermediate mass black holes

## TL;DR

This paper proposes a novel quantum speed meter interferometer design using polarization techniques to enhance low-frequency gravitational wave detection, potentially increasing observable black hole merger events significantly.

## Contribution

It introduces a new QND speed meter concept for gravitational wave detectors using polarization and circulator coupling, improving low-frequency sensitivity.

## Key findings

- Enhanced low-frequency sensitivity in GW detection.
- Potential increase in observable black hole merger events by up to 300 times.
- Robustness analysis against imperfections and optical loss.

## Abstract

The recent discovery of gravitational waves (GW) by LIGO has impressively launched the novel field of gravitational astronomy and it allowed us to glimpse at exciting objects we could so far only speculate about. Further sensitivity improvements at the low frequency end of the detection band of future GW observatories rely on quantum non-demolition (QND) methods to suppress fundamental quantum fluctuations of the light fields used to readout the GW signal. Here we invent a novel concept of how to turn a conventional Michelson interferometer into a QND speed meter interferometer with coherently suppressed quantum back-action noise by using two orthogonal polarisations of light and an optical circulator to couple them. We carry out a detailed analysis of how imperfections and optical loss influence the achievable sensitivity and find that the configuration proposed here would significantly enhance the low frequency sensitivity and increase the observable event rate of binary black hole coalescences in the range of $10^2-10^3 M_\odot$ by a factor of up to $\sim300$.