Quantum relays and noise suppression using linear optics

B. C. Jacobs, T. B. Pittman, J. D. Franson

Published 2002-04-17, updated 2002-05-03Version 2

Probabilistic quantum non-demolition (QND) measurements can be performed using linear optics and post-selection. Here we show how QND devices of this kind can be used in a straightforward way to implement a quantum relay, which is capable of extending the range of a quantum cryptography system by suppressing the effects of detector noise. Unlike a quantum repeater, a quantum relay system does not require entanglement purification or the ability to store photons.