Quantum interference of biphotons at a blazed grating

TL;DR

This paper demonstrates quantum interference of biphotons at a blazed grating, revealing their reduced de Broglie wavelength and analyzing spatial correlations, with implications for quantum imaging resolution enhancement.

Contribution

It experimentally shows biphoton diffraction at a blazed grating and highlights the importance of higher order spatial modes for observing quantum interference effects.

Findings

Biphotons exhibit a de Broglie wavelength of lambda/2 after diffraction.

Higher order spatial modes are crucial for strong spatial correlations.

Experimental verification using parametric down conversion.

Abstract

Correlations between photons are interesting for a number of applications and concepts in metrology in particular for resolution improvements in different methods of quantum imaging. Since Fock-states of N-photons of wavelength lambda in interference schemes acquire N-times the phase shift of single photons these states can appear as if they had a de Broglie wavelength of lambda/N. A biphoton beam diffracted at a blazed grating shows this reduced de Broglie wavelength. This experiment can be seen as a purification of biphotons of a certain correlation strength on the one hand. On the other hand the evaluation of the one-photon and two-photon rate distributions in the Fraunhofer far field of the grating allows for an analysis of the spatial correlation between the photons. An experimental demonstration of these ideas tested for a biphoton beam generated by parametric down conversion (PDC) is reported. We demonstrate in addition that the existence of higher order spatial modes is important to observe strong spatial correlations and to observe the photonic de Broglie wavelength of lambda/2 for biphotons.