Probing Quantum Structure in Gravitational Radiation

TL;DR

This paper proposes experimental tests to determine whether gravitational waves are adequately described by classical coherent states or require a quantum mechanical treatment, potentially revealing new physics.

Contribution

It introduces practical methods to test the quantum nature of gravitational radiation using resonant detectors and interferometers, highlighting circumstances where classical descriptions may fail.

Findings

Tests can distinguish thermal or squeezed states from coherent states

Identifies conditions where classical hypothesis likely fails

Provides a pathway to observe quantum effects in gravitational waves

Abstract

Gravitational radiation from known astrophysical sources is conventionally treated classically. This treatment corresponds, implicitly, to the hypothesis that a particular class of quantum-mechanical states -- the so-called coherent states -- adequately describe the gravitational radiation field. We propose practicable, quantitative tests of that hypothesis using resonant bar detectors monitored in coincidence with LIGO-style interferometers. Our tests readily distinguish fields that contain significant thermal components or squeezing. We identify concrete circumstances in which the classical (i.e., coherent state) hypothesis is likely to fail. Such failures are of fundamental interest, in that addressing them requires us to treat the gravitational field quantum-mechanically, and they open a new window into the dynamics of gravitational wave sources.