Significant-loophole-free test of Kochen-Specker contextuality using two species of atomic-ions

TL;DR

This paper reports a loophole-free experimental test of quantum contextuality using two different atomic ions, closing major loopholes and confirming the nonclassical nature of quantum measurements.

Contribution

First experimental demonstration of loophole-free quantum contextuality test using two different ion species with high detection efficiency and measurement compatibility.

Findings

Violation of noncontextual bounds confirmed

Detection and sharpness loopholes closed

Compatibility loophole closed by using different ions and measurement setups

Abstract

Quantum measurements cannot be thought of as revealing preexisting results, even when they do not disturb any other measurement in the same trial. This feature is called contextuality and is crucial for the quantum advantage in computing. Here, we report the first observation of quantum contextuality simultaneously free of the detection, sharpness and compatibility loopholes. The detection and sharpness loopholes are closed by adopting a hybrid two-ion system and highly efficient fluorescence measurements offering a detection efficiency of $100\%$ and a measurement repeatability $>98\%$. The compatibility loophole is closed by targeting correlations between observables for two different ions in a Paul trap, a $^{171}\mathrm{Yb}^{+}$ ion and a $^{138}\mathrm{Ba}^{+}$ ion, chosen so measurements on each ion use different operation laser wavelengths, fluorescence wavelengths, and detectors. The experimental results show a violation of the bound for the most adversarial noncontextual models and open a new way to certify quantum systems.