An Improved Bound on Nonlinear Quantum Mechanics using a Cryogenic Radio Frequency Experiment

TL;DR

This paper reports a cryogenic RF experiment testing for nonlinear effects in quantum mechanics, setting the most stringent limit to date and improving previous bounds by nearly fifty times.

Contribution

It introduces a novel experimental setup using quantum-generated randomness and spectral analysis to constrain nonlinear quantum effects with unprecedented precision.

Findings

No detectable nonlinear signal was observed.

Established a new upper limit on electromagnetic nonlinearity parameter.

Improved the experimental bound by a factor of nearly 50.

Abstract

There are strong arguments that quantum mechanics may be nonlinear in its dynamics. A discovery of nonlinearity would hint at a novel understanding of the interplay between gravity and quantum field theory, for example. As such, experiments searching for potential nonlinear effects in the electromagnetic sector are important. Here we outline such an experiment, consisting of a stream of random bits (which were generated using Rigetti's Aspen-M-3 chip) as input to an RF signal generator coupled to a cryogenic detector. Projective measurements of the qubit state, which is originally prepared in an equal superposition, serve as the random binary output of a signal generator. Thereafter, spectral analysis of the RF detector would yield a detectable excess signal predicted to arise from such a nonlinear effect. A comparison between the projective measurements of the quantum bits vs the classical baseline showed no power excess. This sets a new limit on the electromagnetic nonlinearity parameter $|\epsilon| \lessapprox 1.15 \times 10^{-12}$, at a 90.0% confidence level. This is the most stringent limit on nonlinear quantum mechanics thus far and an improvement by nearly a factor of 50 over the previous experimental limit.