Quantum Network Testbed

A document describes the world’s first quantum network testbed — an Internet-compatible fiber-optic data-communication network that is kept extremely secure by use of encryption with quantum key distribution (QKD). The testbed, located in the Boston metropolitan area, includes ten nodes, of which four run continuously over commercial telecommunication fiber-optic links, four utilize free-space optical links, and two are based on propagation of polarization-entangled photon pairs in optical fibers. The document contains an introduction to quantum cryptography, including the basic concepts of, and the rationale for, QKD as implemented in the network. The document goes on to describe the architecture of the network and the design and operation of key systems, subsystems, and components. An important consideration affecting the designs of systems and subsystems is the need to formulate QKD algorithms to foil quantum eavesdropping.