Quantum repeaters with entangled coherent states

TL;DR

This paper evaluates the effectiveness of quantum repeaters using entangled coherent states for long-distance quantum communication, finding current technology limitations compared to single-photon approaches.

Contribution

It provides an analysis of entangled coherent state-based repeaters and compares their performance with single-photon entanglement methods, highlighting current technological constraints.

Findings

Current photon counters and memories limit entanglement rates.

Entangled coherent state repeaters do not outperform single-photon repeaters with existing technology.

Potential improvements include advanced parity measurements.

Abstract

Entangled coherent states can be prepared remotely by subtracting non-locally a single photon from two quantum superpositions of coherent states, the so-called "Schroedinger's cat" state. Such entanglement can further be distributed over longer distances by successive entanglement swapping operations using linear optics and photon-number resolving detectors. The aim of this paper is to evaluate the performance of this approach to quantum repeaters for long distance quantum communications. Despite many attractive features at first sight, we show that, when using state-of-the-art photon counters and quantum memories, they do not achieve higher entanglement generation rates than repeaters based on single-photon entanglement. We discuss potential developments which may take better advantage of the richness of entanglement based on continuous variables, including in particular efficient parity measurements.