Experimental violation of the Leggett-Garg inequality with a single-spin system

TL;DR

This paper reports an experimental violation of the Leggett-Garg inequality using a three-level nitrogen-vacancy center in diamond, demonstrating quantum behavior beyond classical bounds with high confidence.

Contribution

It presents the first experimental violation of the Leggett-Garg inequality in a three-level system using ideal negative result measurement.

Findings

Leggett-Garg function exceeds L"uders bound with 5σ confidence

Demonstrates quantum superposition in a macroscopic system

Uses nitrogen-vacancy center in diamond for the experiment

Abstract

Investigation the boundary between quantum mechanical description and classical realistic view is of fundamental importance. The Leggett-Garg inequality provides a criterion to distinguish between quantum systems and classical systems, and can be used to prove the macroscopic superposition state. A larger upper bound of the LG function can be obtained in a multi-level system. Here, we present an experimental violation of the Leggett-Garg inequality in a three-level system using nitrogen-vacancy center in diamond by ideal negative result measurement. The experimental maximum value of Leggett-Garg function is $K_{3}^{exp}=1.625\pm0.022$ which exceeds the L\"uders bound with a $5\sigma$ level of confidence.