In this paper, we investigate the performance of orthogonal frequency division multiplexed quantum key distribution (OFDM-QKD) in an integrated quantum-classical wavelength-division-multiplexing system. The presence of an intense classical signal alongside the quantum one generates Raman background noise. Noise reduction techniques should, then, be carried out at the receiver to suppress this crosstalk noise. In this work, we show that OFDM-QKD enables eﬃcient filtering, in time and frequency domains, making it an attractive solution for the high-rate links at the core of quantum-classical networks.
Quantum repeaters enable us to distribute entanglement between remote parties by relying on a network of quantum
memory units that exhibit efficient coupling to light, scalability, and long coherence times. Entanglement
is initially distributed between nearest neighbors and then extended to the far-end nodes using entanglement
swapping techniques. For real-time applications, such as quantum key distribution, the above tasks must be
repeated successively, according to a proper protocol, to generate entangled states at a certain rate. This paper
studies a number of such protocols and the interplay between the rate of entanglement generation, the number
of employed memories, and the coherence time of memory units.
The architecture proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) for entangling distant atomic ensembles is addressed and analyzed. Its performance, in terms of fidelity and throughput, is compared to that of the quantum communication architecture using trapped rubidium-atom quantum memories that has been proposed by a team from the Massachusetts Institute of Technology and Northwestern University (MIT/NU). It is shown that the DLCZ protocol for entanglement distribution achieves a better throughput versus distance behavior than does the MIT/NU architecture, with both being capable of high entanglement fidelities. The DLCZ scheme also admits to a conditional teleportation scheme based on its entangled atomic ensembles, whereas the MIT/NU architecture affords unconditional teleportation based on its trapped-atom quantum memories. It is shown that achieving unity fidelity in DLCZ teleportation requires photon-number resolving detectors; the maximum teleportation fidelity that can be realized with non-resolving detectors is 1/2.