Fundamental building block for all-optical scalable quantum networks

TL;DR

This paper establishes the fundamental physical limits of all-optical Bell measurements for quantum communication, proposes a scheme to reach these limits, and demonstrates its potential to enable scalable, long-distance quantum networks.

Contribution

It derives the ultimate physical limits of all-optical Bell measurements and introduces a scheme that achieves these limits, advancing scalable quantum communication.

Findings

The fundamental limits of efficiency and loss-tolerance are derived based on physics laws.

A linear optics Bell measurement scheme is proposed that reaches these fundamental limits.

The proposed scheme enables fast, efficient, long-distance quantum communication surpassing previous protocols.

Abstract

Major obstacles against efficient long distance quantum communication are photon losses during transmission and the probabilistic nature of Bell measurement causing exponential scaling in time and resource with distance. To overcome these difficulties, while conventional quantum repeaters require matter-based operations with long-lived quantum memories, recent proposals have employed encoded multiple photons in entanglement, providing an alternative way for scalability. In pursuing scalable quantum communications, naturally arising questions are thus whether any ultimate limit exists in all-optical scalability, and whether and how it can be achieved. Motivated by these questions, we derive the fundamental limits of the efficiency and loss-tolerance of the Bell measurement with multiple photons, restricted not by protocols but by the laws of physics, i.e. linear optics and no-cloning theorem. We then propose a Bell measurement scheme with linear optics, which enables one to reach both the fundamental limits: one by linear optics and the other by the no-cloning theorem. The quantum repeater based on our scheme allows one to achieve fast and efficient quantum communication over arbitrary long distances, outperforming previous all-photonic and matter-based protocols. Our work provides a fundamental building block for quantum networks within but toward the ultimate limits of all-optical scalability.