Quantum Repeaters using Coherent-State Communication

TL;DR

This paper explores quantum repeater protocols that utilize optical coherent-state communication to distribute entanglement between atomic qubits, aiming to improve fidelity and scalability in quantum networks.

Contribution

It introduces measurement schemes, including unambiguous state discrimination, to eliminate spin-flip errors and enhance quantum repeater performance using coherent states.

Findings

Unambiguous state discrimination reduces spin-flip errors.

High initial fidelities achieved with weaker coherent states.

Protocols resemble single-photon schemes at larger distances.

Abstract

We investigate quantum repeater protocols based upon atomic qubit-entanglement distribution through optical coherent-state communication. Various measurement schemes for an optical mode entangled with two spatially separated atomic qubits are considered in order to nonlocally prepare conditional two-qubit entangled states. In particular, generalized measurements for unambiguous state discrimination enable one to completely eliminate spin-flip errors in the resulting qubit states, as they would occur in a homodyne-based scheme due to the finite overlap of the optical states in phase space. As a result, by using weaker coherent states, high initial fidelities can still be achieved for larger repeater spacing, at the expense of lower entanglement generation rates. In this regime, the coherent-state-based protocols start resembling single-photon-based repeater schemes.