Variational readout through quantum teleportation

TL;DR

This paper proposes a quantum teleportation-based method for variational readout in gravitational-wave detectors, aiming to reduce filter cavity requirements and explore true back action evasion techniques.

Contribution

It introduces a novel quantum teleportation approach for variational readout that eliminates the need for long filter cavities in gravitational-wave detectors.

Findings

The teleportation scheme does not outperform EPR squeezing in variational readout.

Current methods do not achieve true back action evasion.

The paper stimulates discussion on realizing genuine back action evasion techniques.

Abstract

Sensitivity of gravitational-wave detectors (GWDs) is constrained at low frequencies by quantum radiation-pressure noise, a manifestation of the measurement's back action. One strategy to mitigate this back action involves employing variational readout, which entails cross-correlating the measurement shot noise with radiation-pressure noise. Prior research has demonstrated that variational readout in GWDs can be accomplished through the use of a filter cavity. However, current gravitational-wave detectors necessitate filter cavity lengths on the order of $\sim 100$ meters, with future detectors anticipated to reach lengths of a few kilometers. This paper introduces a novel approach to variational readout utilizing principle of quantum teleportation, which eliminates the need for a filter cavity. *This document will not be published any journals, since it turned out to be not very useful for the real detectors. The main reason is that one does not need the EPR entanglement to obtain the same result, which does not even shows true variational readout. In other words, both schemes do not exceed the EPR squeezing. Nevertheless this document will be uploaded to stimulate discussions how to realize "true" back action evasion, such as variational readout or speed meter, via quantum entanglement.