An Optimized Photon Pair Source for Quantum Circuits

TL;DR

This paper presents an ultrafast, highly indistinguishable photon pair source using a periodically poled KTP waveguide, achieving high purity and efficiency without narrowband filtering, suitable for quantum circuit applications.

Contribution

The work introduces a nearly pure, indistinguishable photon pair source with high heralding efficiency, optimized for quantum circuits, using a novel waveguide implementation at telecom wavelengths.

Findings

Schmidt number below 1.16 indicating high mode purity

94.8% interference visibility between signal and idler photons

Heralding efficiencies of 20.5% and 15.5% (corrected to 80% and 70%)

Abstract

We implement an ultrafast pulsed type-II parametric down conversion source in a periodically poled KTP waveguide at telecommunication wavelengths with almost identical properties between signal and idler. As such, our source resembles closely a pure, genuine single mode photon pair source with indistinguishable modes. We measure the joint spectral intensity distribution and second order correlation functions of the marginal beams and find with both methods very low effective mode numbers corresponding to a Schmidt number below 1.16. We further demonstrate the indistinguishability as well as the purity of signal and idler photons by Hong-Ou-Mandel interferences between signal and idler and between signal/idler and a coherent field, respectively. Without using narrowband spectral filtering, we achieve a visibility for the interference between signal and idler of 94.8% and determine a purity of more than 80% for the heralded single photon states. Moreover, we measure raw heralding efficiencies of 20.5% and 15.5% for the signal and idler beams corresponding to detector-loss corrected values of 80% and 70%.