Abstract

Entanglement distribution over optical fiber is an important backbone technology that would enable quantum communication applications such as quantum cryptography and quantum teleportation within local-area networks [1]. Although photons are excellent carriers of quantum entanglement, they experience loss during transmission and cannot be amplified. This generally leads to very low distribution rates. From an engineering point of view, photon transmission rate should be maximized by full utilization of the available optical fiber transmission bandwidth. As a first step towards this goal, we have proposed a broadband source of high quality polarization-entangled photon-pairs [2] and demonstrated wavelength-multiplexed entanglement distribution over optical fiber [3]. By further combining the outputs from two broadband entangled photon-pair sources as shown in Fig. 1, very efficient fiber transmission bandwidth utilization for entanglement distribution can in principle be achieved. In this work, we emphasize the importance of properly designing a bandwidth-resource-efficient entanglement distribution system. In particular, we point out that inappropriate setting of wavelength demultiplexing channel bandwidth with respect to pump spectral width could affect entanglement quality. It is widely known that the photon coherence length can be made longer than pump pulsewidth by narrowband filtering so as to improve photon temporal coherence [4], however, the excess noise that accompanies narrowband filtering has not been studied. The use of narrowband sources of entangled photon-pairs avoids this problem but one needs to wavelength-multiplex many such narrowband sources in order to implement bandwidth-resource-efficient entanglement distribution. We show how to reduce excess noise while maintaining a high photon temporal coherence for a bandwidth-resource-efficient system that uses broadband sources (Fig. 1).

© 2009 IEEE