Fundamental building block for all-optical scalable quantum networks

Understand

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.