# Optimal photon pairs for quantum communication protocols

## TL;DR

This paper develops a theoretical method to optimize photon pair characteristics from SPDC sources for fiber-based quantum communication, enhancing noise reduction and security distance in quantum key distribution.

## Contribution

It introduces a strategy to optimize SPDC photon properties using accessible parameters, improving quantum communication performance and security.

## Key findings

- Optimized SPDC parameters reduce photon temporal width.
- Full source optimization extends quantum key distribution distance by ~30%.
- Comparison with BBO crystal sources validates the approach.

## Abstract

We theoretically investigate the problem of finding optimal characteristics of photon pairs, produced in the spontaneous parametric down-conversion (SPDC) process, for fiber-based quantum communication (QC) protocols. By using the accessible setup parameters, the pump pulse duration and the extended phase-matching function width, we minimize the temporal width of SPDC photons within the general scenario. This allows one to perform more effectively the temporal filtering procedure, which aims at reducing the noise acquired by the measurement devices. Moreover, we compare the obtained results with the achievable parameter values for SPDC sources based on $\beta$-Barium Borate (BBO) crystal. We also investigate the influence of non-zero detection timing jitter. Finally, we apply our optimization strategy to a simple quantum key distribution scheme to show that the full optimization of an SPDC source can potentially extend the maximal security distance by several tens of kilometres, which is around 30\% more as compared to previous approaches.