Feasibility considerations for free-fall tests of gravitational decoherence

TL;DR

This paper evaluates the practicality of space-based free-fall experiments to test gravitational decoherence, concluding that interferometric methods are necessary for conclusive results due to limitations in non-interferometric approaches.

Contribution

It analyzes the feasibility of non-interferometric space experiments for gravitational decoherence and argues that interferometric methods are essential for definitive testing.

Findings

Non-interferometric experiments face practical limitations in data collection.

Interferometric approaches are required for conclusive tests of gravitational decoherence.

Space environment offers advantages like long free-fall times and low noise.

Abstract

Space offers exciting opportunities to test the foundations of quantum physics using macroscopic quantum superpositions. It has been proposed to perform such tests in a dedicated space mission (MAQRO) using matter-wave interferometry with massive test particles or monitoring how the wave function of a test particle expands over time. Such experiments could, test quantum physics with sufficiently high precision to resolve potential deviations from its unitary evolution due to gravitational decoherence. For example, such deviations have been predicted by the Di\'{o}si-Penrose (DP) model and the K\'{a}rolyh\'{a}zy (K) model. The former predicts the collapse of massive or large superpositions due to a non-linear modification of quantum evolution. The latter predicts decoherence because of an underlying uncertainty of space time. Potential advantages of a space environment are (1) long free-fall times, (2) low noise, and (3) taking a high number of data points over several years in a dedicated space mission. In contrast to interferometric tests, monitoring wave function expansion is less complex, but it does face some practical limitations. Here, we will discuss limitations of such non-interferometric experiments due to the limited number of data points achievable during a mission lifetime. Our results show that it will require an interferometric approach to conclusively test for gravitational decoherence as predicted by the DP or K models. In honor of the novel prize of Sir Roger Penrose, we will focus our discussion on the Di\'{o}si-Penrose model.