Entanglement Enabled Intensity Interferometry of Different Wavelengths of Light

TL;DR

This paper introduces a method for performing intensity interferometry on photons of different wavelengths using entanglement and nonlinear crystals, enabling new measurements of frequency correlations and improved source resolution.

Contribution

It presents a novel approach to enable interference between photons of different wavelengths through entanglement and projection, expanding the capabilities of intensity interferometry.

Findings

Demonstrates how nonlinear crystals can convert different wavelengths to a common wavelength while preserving phase.

Generalizes the van Cittert-Zernike formula for extended sources with spectral diversity.

Shows potential for enhanced resolution and new observables in optical interferometry.

Abstract

We propose methods to perform intensity interferometry of photons having two different wavelengths. Distinguishable particles typically cannot interfere with each other, but we overcome that obstacle by processing the particles via entanglement and projection so that they lead to the same final state at the detection apparatus. Specifically, we discuss how quasi-phase-matched nonlinear crystals can be used to convert a quantum superposition of light of different wavelengths onto a common wavelength, while preserving the phase information essential for their meaningful interference. We thereby gain access to a host of new observables, which can probe subtle frequency correlations and entanglement. Further, we generalize the van Cittert-Zernike formula for the intensity interferometry of extended sources, demonstrate how our proposal supports enhanced resolution of sources with different spectral character, and suggest potential applications.