Experimental violation of the Leggett-Garg inequality under decoherence

TL;DR

This paper experimentally tests the Leggett-Garg inequalities using single photons under decoherence, demonstrating their violation diminishes with environmental interaction, thus probing the quantum-classical boundary.

Contribution

It provides the first experimental investigation of LG inequalities under decoherence simulated by birefringent media, revealing how environmental effects influence quantum violations.

Findings

LG inequalities are maximally violated in coherent evolution.

Violation strength decreases with increased environmental interaction.

Results help define the boundary between quantum and classical regimes.

Abstract

Despite the great success of quantum mechanics, questions regarding its application still exist and the boundary between quantum and classical mechanics remains unclear. Based on the philosophical assumptions of macrorealism and noninvasive measurability, Leggett and Garg devised a series of inequalities (LG inequalities) involving a single system with a set of measurements at different times. Introduced as the Bell inequalities in time, the violation of LG inequalities excludes the hidden-variable description based on the above two assumptions. We experimentally investigated the single photon LG inequalities under decoherence simulated by birefringent media. These generalized LG inequalities test the evolution trajectory of the photon and are shown to be maximally violated in a coherent evolution process. The violation of LG inequalities becomes weaker with the increase of interaction time in the environment. The ability to violate the LG inequalities can be used to set a boundary of the classical realistic description.