Optimizing entanglement distribution via noisy quantum channels

TL;DR

This paper analyzes strategies for distributing entanglement over noisy quantum channels, showing the midpoint placement is often optimal and developing SDP methods to quantify achievable entanglement.

Contribution

It demonstrates the optimality of the midpoint entanglement source placement and introduces SDP techniques to evaluate entanglement distribution capabilities.

Findings

Midpoint strategy is optimal for certain qubit channels.

SDP methods effectively quantify maximum entanglement distribution.

Weakly entangled inputs are often necessary for successful distribution.

Abstract

Entanglement distribution is a crucial problem in quantum information science, owing to the essential role that entanglement plays in enabling advanced quantum protocols, including quantum teleportation and quantum cryptography. We investigate strategies for distributing quantum entanglement between two distant parties through noisy quantum channels. Specifically, we compare two configurations: one where the entanglement source is placed at the midpoint of the communication line, and another where it is located at one end. For certain families of qubit channels we show analytically that the midpoint strategy is optimal. Based on extensive numerical analysis, we conjecture that this strategy is generally optimal for all qubit channels. Focusing on the midpoint configuration, we develop semidefinite programming (SDP) techniques to assess whether entanglement can be successfully distributed through the network, and to quantify the amount of entanglement that can be distributed in the process. In many relevant cases the SDP formulation reliably captures the maximal amount of entanglement which can be distributed, if entanglement is quantified using the negativity. We analyze several channel models and demonstrate that, for various combinations of amplitude damping and depolarizing noise, entanglement distribution is only possible with weakly entangled input states. Excessive entanglement in the input state can hinder the channel's ability to establish entanglement. Our findings have implications for optimizing entanglement distribution in realistic quantum communication networks.