Towards an Experimental Test of Gravity-induced Quantum State Reduction

TL;DR

This paper investigates the possibility of experimentally testing gravity-induced quantum state reduction, analyzing various macroscopic quantum systems and their potential to reveal gravitational effects on quantum coherence.

Contribution

It extends Penrose's hypothesis to superpositions of mass current states and evaluates the feasibility of observing gravitational state reduction with current technology.

Findings

Micromechanical states unlikely to suppress environmental decoherence

Cold atom condensates lack sufficient mass scale

Flux qubits approach measurable gravitational effects

Abstract

According to the hypothesis of Penrose and Diosi, quantum state reduction is a manifestation of the incompatibilty of general relativity and the unitary time evolution of quantum physics. Dimensional analysis suggests that Schrodinger cat type states should collapse on measurable time scales when masses and lengths of the order of bacterial scales are involved. We analyze this hypothesis in the context of modern developments in condensed matter and cold atoms physics, aimed at realizing macroscopic quantum states. We first consider 'micromechanical' quantum states, analyzing the capacity of an atomic force microscopy based single spin detector to measure the gravitational state reduction, but we conclude that it seems impossible to suppress environmental decoherence to the required degree. We subsequently discuss 'split' cold atom condensates to find out that these are at present lacking the required mass scale by many orders of magnitude. We then extent Penrose's analysis to superpositions of mass current carrying states, and we apply this to the flux quantum bits realized in superconducting circuits. We find that the flux qubits approach the scale where gravitational state reduction should become measurable, but bridging the few remaining orders of magnitude appears to be very difficult with present day technology.