An optomechanical Bell test

TL;DR

This paper demonstrates a Bell inequality violation using a macroscopic optomechanical system, confirming non-classical behavior in a large-scale mechanical device through light-matter entanglement.

Contribution

It presents the first violation of a Bell inequality involving a massive, macroscopic mechanical system with optomechanical oscillators.

Findings

Bell inequality violated by more than 4 standard deviations

Entanglement established between mechanical motion and optical modes

Confirms non-classical behavior in large-scale mechanical systems

Abstract

Over the past few decades, experimental tests of Bell-type inequalities have been at the forefront of understanding quantum mechanics and its implications. These strong bounds on specific measurements on a physical system originate from some of the most fundamental concepts of classical physics - in particular that properties of an object are well defined independent of measurements (realism) and only affected by local interactions (locality). The violation of these bounds unambiguously shows that the measured system does not behave classically, void of any assumption on the validity of quantum theory. It has also found applications in quantum technologies for certifying the suitability of devices for generating quantum randomness, distributing secret keys and for quantum computing. Here we report on the violation of a Bell inequality involving a massive, macroscopic mechanical system. We create light-matter entanglement between the vibrational motion of two silicon optomechanical oscillators, each comprising approx. $10^{10}$ atoms, and two optical modes. This state allows us to violate a Bell inequality by more than 4 standard deviations, directly confirming the non-classical behavior of our optomechanical system under the fair sampling assumption.