Squeezed States in Gravity

TL;DR

This paper introduces a framework for generating squeezed quantum states of gravity via time-dependent couplings in linearized quantum gravity, highlighting how classical backgrounds and matter sources can produce such states.

Contribution

It provides a general method to produce and analyze squeezed states of the gravitational field in linearized quantum gravity, including techniques to determine the squeezing parameter.

Findings

Quadratic couplings in the gravitational action lead to squeezed states.

Time-dependent backgrounds and matter sources generate gravitational squeezing.

Three methods to extract the squeezing parameter are described.

Abstract

We present a general framework for the production of squeezed quantum states of the gravitational field in linearized quantum gravity. Time-dependent couplings in the quadratic part of the action generically produce squeezed states from the vacuum. Using the harmonic oscillator as an example, we describe three techniques to obtain the squeezing parameter from such quadratic terms. For gravity, the action to quadratic order in metric perturbations contains couplings both to background curvature as well as to matter sources. Thus, both time-dependent classical spacetimes and time-dependent classical matter typically produce squeezed states of gravity.