Efficient single-spatial-mode periodically-poled KTiOPO_4 waveguide source for high-dimensional entanglement-based quantum key distribution

TL;DR

This paper presents a highly efficient, single-spatial-mode PPKTP waveguide source for generating high-purity photon pairs at 1560 nm, enabling high-rate quantum key distribution with high interference visibility.

Contribution

The work introduces a PPKTP waveguide source with nearly lossless spectral filtering and high coupling efficiency, optimized for high-dimensional entanglement-based quantum key distribution.

Findings

Achieved >1 Mbit/s raw key rate with 3 bits-per-photon encoding.

Demonstrated 98.2% Franson quantum-interference visibility.

Produced high-purity photon pairs in a single spatial mode.

Abstract

We demonstrate generation of high-purity photon pairs at 1560 nm in a single spatial mode from a periodically-poled KTiOPO_4 (PPKTP) waveguide. With nearly lossless spectral filtering, the PPKTP waveguide source shows approximately 80 % single-mode fiber coupling efficiency and is well suited for high-dimensional time-energy entanglement-based quantum key distribution. Using high-count-rate self-differencing InGaAs single-photon avalanche photodiodes configured with either square or sinusoidal gating, we achieve > 1 Mbit/s raw key generation with 3 bits-per-photon encoding, and, to the best of our knowledge, the highest reported Franson quantum-interference visibility of 98.2 % without subtraction of accidental coincidences.