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Frontiers in Optics

Experimental Violation of the Leggett-Garg Inequality with Classical Light

Wenlei Zhang, Ravi K. Saripalli, Jacob M. Leamer, Ryan T. Glasser, Denys I. Bondar

Published Jan 1, 2021• 0 citations
Publisher

Abstract

We present an experimental violation of the Leggett-Garg inequality in classical optics using only the polarization degree-of-freedom of a laser beam. Our results show maximum violations of the Leggett-Garg inequality.
DOI
10.1364/fio.2021.jth5a.36

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Abstract Leggett-Garg (LG) inequalities have been derived to clarify the validity of generalizing quantum mechanics to macroscopic systems for more than thirty years. They have been used as tools to investigate the existence of quantum coherence in macroscopic systems. Here, we show that such inequality violation can also be observed in classical optical systems. Using the linear polarization degree of freedom as the dichotomic observables, in a classical optical experiment, we have observed the violation of LG inequality by implementing the non-invasive measurement. Furthermore, the coherence witness, which is analogous to the quantum witness, has also been observed in the classical optical experiment. Our results not only provide new physical insights into the macroscopic quantum correlation and quantum witness, but also show their potential applications in correlated information processes.
By weakly measuring the polarization of a photon between two strong polarization measurements, we experimentally investigate the correlation between the appearance of anomalous values in quantum weak measurements and the violation of realism and nonintrusiveness of measurements. A quantitative formulation of the latter concept is expressed in terms of a Leggett-Garg inequality for the outcomes of subsequent measurements of an individual quantum system. We experimentally violate the Leggett-Garg inequality for several measurement strengths. Furthermore, we experimentally demonstrate that there is a one-to-one correlation between achieving strange weak values and violating the Leggett-Garg inequality.
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