Squeezed States in Gravity

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.