Observation of entanglement between two light beams spanning an octave in optical frequency

TL;DR

This paper reports the experimental demonstration of entanglement between two light beams separated by an octave in frequency, achieved through nonlinear optical interactions in a resonator, advancing quantum optics research.

Contribution

It presents the first experimental observation of entanglement between light beams spanning an octave in frequency using a nonlinear resonator setup.

Findings

Quantum correlations in amplitude and phase quadratures were observed.

The correlation matrix indicated wavefunction inseparability below 1, confirming entanglement.

Abstract

We have experimentally demonstrated how two beams of light separated by an octave in frequency can become entangled after their interaction in a second-order nonlinear medium. The entangler consisted of a nonlinear crystal placed within an optical resonator that was strongly driven by coherent light at the fundamental and second-harmonic wavelengths. An inter-conversion between the fields created quantum correlations in the amplitude and phase quadratures, which were measured by two independent homodyne detectors. Analysis of the resulting correlation matrix revealed a wavefunction inseparability of 0.74(1) < 1 thereby satisfying the criterion of entanglement.