Violation of the Cauchy-Schwarz Inequality in the Macroscopic Regime

TL;DR

This paper reports a significant violation of the Cauchy-Schwarz inequality in a macroscopic setting using quantum-correlated beams, challenging classical assumptions and highlighting the nuanced relationship between squeezing and inequality violations.

Contribution

It demonstrates a macroscopic violation of the Cauchy-Schwarz inequality using bright intensity-difference squeezed beams, showing that squeezing does not always imply inequality violation.

Findings

Observed violation more than 8 standard deviations

Filtered out low frequency noise from quantum-correlated beams

Showed squeezing does not necessarily imply inequality violation

Abstract

We have observed a violation of the Cauchy-Schwarz inequality in the macroscopic regime by more than 8 standard deviations. The violation has been obtained while filtering out only the low frequency noise of the quantum-correlated beams that results from the technical noise of the laser used to generate them. We use bright intensity-difference squeezed beams produced by four-wave mixing as the source of the correlated fields. We also demonstrate that squeezing does not necessarily imply a violation of the Cauchy-Schwarz inequality.