Decoherence of polarization entanglement in optical fibers with polarization mode dispersion

Monday, March 14, 2011 -
4:00pm to 5:00pm
Misha Brodsky
Speaker's Institution: 
AT&T Labs

Quantum mechanics permits the existence of unique correlations, or entanglement, between individual particles. 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.

Several physical phenomena set limitations on transmission of classical light pulses through optical fibers. An intriguing and crucial question is how some of these well-studied phenomena, for instance Polarization Mode Dispersion (PMD), affect a polarization entangled photon pair. 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. In addition, we suggest a novel way to compensate for adverse effects that occur during propagation in fibers. Finally, we define the range of fiber parameters over which entanglement remains sufficient for secure communication. The richness of the observed phenomena suggests that fiber-based entanglement distribution systems could serve as natural laboratories for studying entanglement decoherence.