Quantum mechanics permits the existence of unique correlations, or entanglement, between individual particles. For a pair of entangled photons, this means that performing a measurement on one photon appears to affect the state of the other. The ability of entangled particles to act in concert is preserved even when they are separated by large distances and serves as a resource for numerous applications. For example, distributing entangled photon pairs over fiber-optic cables enables secure communication between two remote parties or could offer the possibility of interconnecting quantum computers. The vast transparency band of the installed global fiber-optic network, consisting of over a Gigameter of optical fiber cables, presents a particularly attractive opportunity for this task. The bond between entangled photons is, however, very fragile and could be lost. How far could one send entangled photons while still maintaining the connection between them?

We investigate, theoretically and experimentally, how inherent defects and miniscule imperfections in fiber-optic cables degrade entanglement between two photons transmitted over fibers. We show that the loss of entanglement could be either gradual or surprisingly abrupt. We describe relation between local and non-local effects and suggest a novel non-local way to compensate for adverse effects that occur during propagation in fibers. The richness of the observed phenomena suggests that fiber-based entanglement distribution systems could serve as natural laboratories for studying entanglement decoherence.

A brief introduction to the topic of the talk is available on the front page of AT&T Labs website: www.research.att.com

Location: Physics Bldg., Room 401