Bright filter-free source of indistinguishable photon pairs

TL;DR

This paper presents a highly efficient, filter-free source of indistinguishable photon pairs using a cavity-enhanced parametric oscillator, achieving high brightness and indistinguishability without filtering.

Contribution

The authors demonstrate a novel, high-brightness photon pair source with over 90% indistinguishability, significantly surpassing previous spectral brightness levels.

Findings

Hong-Ou-Mandel interference visibility >90%

Spectral brightness increased by two orders of magnitude

Achieved 70 pairs/(s mW MHz) rate at 7 MHz linewidth

Abstract

We demonstrate a high-brightness source of pairs of indistinguishable photons based on a type-II phase-matched doubly-resonant optical parametric oscillator operated far below threshold. The cavity-enhanced down-conversion output of a PPKTP crystal is coupled into two single-mode fibers with a mode coupling efficiency of 58%. The high degree of indistinguishability between the photons of a pair is demonstrated by a Hong-Ou-Mandel interference visibility of higher than 90% without any filtering at an instantaneous coincidence rate of 450 000 pairs/s per mW of pump power per nm of down-conversion bandwidth. For the degenerate spectral mode with a linewidth of 7 MHz at 795 nm a rate of 70 pairs/(s mW MHz) is estimated, increasing the spectral brightness for indistinguishable photons by two orders of magnitude compared to similar previous sources.