Extra phase noise from thermal fluctuations in nonlinear optical crystals

TL;DR

Thermal phonons in nonlinear crystals generate phase noise that hampers quantum entanglement in optical parametric oscillators, but cooling the crystal reduces this noise, improving quantum correlations.

Contribution

This work identifies thermal phonon scattering as a source of phase noise in nonlinear crystals and demonstrates noise reduction through cooling, enhancing quantum entanglement.

Findings

Thermal phonons cause additional phase noise in nonlinear crystals.

Cooling the crystal reduces the phase noise.

The noise model applies to various systems in the literature.

Abstract

We show theoretically and experimentally that scattered light by thermal phonons inside a second-order nonlinear crystal is the source of additional phase noise observed in Optical Parametric Oscillators. This additional phase noise reduces the quantum correlations and has hitherto hindered the direct production of multipartite entanglement in a single nonlinear optical system. We cooled the nonlinear crystal and observed a reduction of the extra noise. Our treatment of this noise can be successfully applied to different systems in the literature.