Improvement of entanglement generation rate in frequency-multiplexed quantum repeaters using cavity-enhanced SPDC source

TL;DR

This paper provides a theoretical analysis showing that frequency multiplexing with cavity-enhanced SPDC sources significantly improves entanglement generation rates in quantum repeaters, especially when multiplexing around 100 modes.

Contribution

It derives an approximate quantum state expression for frequency-multiplexed photons and evaluates heralding probability and fidelity improvements with multiplexing in quantum repeaters.

Findings

Heralding probability reaches 98% with 100 modes at 25 km link distance.

Fidelity exceeds 0.9 across all modes in the multiplexed scheme.

Heralding probability increases from 0.7% to 38% at 100 km with multiplexing.

Abstract

High-rate entanglement generation is essential for the realization of practical quantum repeaters. To this end, frequency multiplexing of the photons employed is an effective approach. In particular, schemes using cavity-enhanced spontaneous parametric down-conversion (cSPDC) as a photon-pair source have been proposed. In this study, toward a theoretical performance evaluation of frequency-multiplexed quantum repeaters based on cSPDC, we derive an approximate expression for the quantum state of the frequency-multiplexed photons, where each frequency mode is treated as an independent two-mode squeezed vacuum (TMSV) state. Using this expression, we calculate the heralding probability and fidelity of entanglement generation for several cases in a single-photon interference scheme using frequency multiplexing with cSPDC. Our results demonstrate that by multiplexing approximately 100 modes, the heralding probability improves to approximately 98% for an elementary link distance $L_\mathrm{EL}=25 \mathrm{km}$, even in scenarios where the fidelity exceeds 0.9 across all modes. Furthermore, for $L_\mathrm{EL}=100 \mathrm{km}$, we show that the heralding probability, which was approximately 0.7% in the single-mode case, increases to about 38% under the condition that the fidelity remains 0.9 or higher. These analytical results demonstrate the effectiveness of employing cSPDC as a photon-pair source for quantum repeaters.