Constraining the number of fundamental quantum degrees of freedom using gravity

TL;DR

This paper investigates how gravity induces decoherence in extended quantum systems by modeling gravitational redshift effects, proposing a method to constrain the number of fundamental quantum degrees of freedom through observable superpositions.

Contribution

It introduces a model of gravitational decoherence based on redshift effects and suggests a way to limit the number of undiscovered quantum fields using matter wave interferometry.

Findings

Decoherence increases with the number of gravitationally interacting EQS.

The model predicts observable effects in matter wave interferometry.

Analysis of spin chains shows parameter dependence of the decoherence effect.

Abstract

We consider the effect of gravity on extended quantum systems (EQS) in the low energy regime. We model the gravitational effect due to a nearby source mass as a redshift in the internal Hamiltonian of the EQS. Due to the dependence of the energy spectrum of the EQS on the position of the massive particle (via the redshift) at zero temperature, our model predicts gravitational decoherence of the massive particle in the position basis. We show that the decoherence effect is multiplicative, in the sense that the increase in number of EQS gravitationally interacting with a single massive particle leads to an increase in its decoherence. If the considered model of gravitational redshift holds alongside the linearity of quantum mechanics (as an appropriate limit of an accepted theory for coupling quantum matter with gravity) to allow for a spatial superposition of the source mass, we propose that the same methodology can be applied to continuous fields, which are essentially EQS. This could provide an upper limit on the number of undiscovered fields by observing coherent superpositions of masses, e.g., in a matter wave interferometer. Besides, by taking a spin chain as a toy model of an EQS, we analyse the dependence of the new effect on relevant system parameters and identify the number of independent spin chains that can cause a detectable effect.