The DARPA Quantum Network
To a surprising extent, however, these limitations can be mitigated or even completely removed by building QKD networks instead of the traditional stand-alone QKD links. Accordingly, a team of participants from BBN Technologies, Boston University, and Harvard University has recently built and begun to operate the world’s first quantum key distribution network under Defense Advanced Research Projects Agency (DARPA) sponsorship.∗
The DARPA Quantum Network became fully operational on October 23, 2003, in BBN’s laboratories, and in June 2004 it was fielded through dark fiber underneath the streets of Cambridge, Massachusetts, to link our campuses with nonstop quantum cryptography, 24 hours per day. It is the world’s first quantum cryptography network and indeed probably the first metro-area QKD deployment in continuous operation. As of December 2004, it consists of six QKD nodes. Four are used in BBN-built, interoperable weak-coherent QKD systems running at a 5-MHz pulse rate through telecommunications fiber and inter-connected via a photonic switch. Two are electronics built by the National Institute of Standards and Technology (NIST) for a high-speed free-space QKD system. All run BBN’s full suite of production-quality QKD protocols. In the near future, we plan to add four more quantum cryptographic nodes based on a variety of physical phenomena and start testing the resulting network against sophisticated attacks.