Opening up the Quantum Three-Box Problem with Undetectable Measurements

TL;DR

This paper demonstrates a quantum experiment using nitrogen vacancy centers that rules out classical explanations by showing measurement effects incompatible with classical models, addressing the measurement detectability loophole in quantum mechanics.

Contribution

It implements a three-box quantum game with undetectable measurements, providing the first experimental exclusion of macroscopic state-definiteness and addressing the measurement detectability loophole.

Findings

Classical models are statistically ruled out by >7.8 standard deviations.

The experiment excludes the property of macroscopic state-definiteness.

It serves as a Kochen-Specker test of quantum non-contextuality.

Abstract

One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained as the back-action required by quantum mechanics adding quantum noise to a classical signal. Here we implement the 'three-box' quantum game of Aharonov and Vaidman in which quantum measurements add no detectable noise to a classical signal, by utilising state-of-the-art control and measurement of the nitrogen vacancy centre in diamond. Quantum and classical mechanics then make contradictory predictions for the same experimental procedure, however classical observers cannot invoke measurement-induced disturbance to explain this discrepancy. We quantify the residual disturbance of our measurements and obtain data that rule out any classical model by > 7.8 standard deviations, allowing us for the first time to exclude the property of macroscopic state-definiteness from our system. Our experiment is then equivalent to a Kochen-Spekker test of quantum non-contextuality that successfully addresses the measurement detectability loophole.