Quantum Repeaters: The Role of Imperfect Local Operations in Quantum Communication

Abstract

We present an exact model of the detection statistics of a probabilistic source of photon pairs from which a fast, simple and precise method to measure the source's brightness and photon channel transmissions is demonstrated. We measure such properties for a source based on spontaneous parametric downconversion in a periodically poled LiNbO 3 crystal producing pairs at 810 and 1550 nm wavelengths. We further validate the model by comparing the predicted and measured values for the g (2) (0) of a heralded single photon source over a wide range of the brightness. Our model is of particular use for monitoring and tuning the brightness on demand as required for various quantum communication applications. We comment on its applicability to sources involving spectral and/or spatial filtering.

The Case for Quantum Key Distribution

“…Quantum repeaters [BDCZ98] would also overcome the distance limitation, allowing shared quantum states to be established between distant parties. While these systems are not yet operational, they are easier to implement than full-scale quantum computers; theoretical and experimental work progresses on their development.…”

The SECOQC quantum key distribution network in Vienna

“…End-to-end quantum-channel-based networks could be created by using quantum repeaters [27,28] that are not yet technically realized. Current technology allows, however, optical switching (whereby switching is meant in general terms as some appropriate active or passive classical optical function) that can be applied to the quantum signals in order to create physically, so to say on demand, a direct quantum channel.…”

“…The steps down (each of size 728 bytes) correspond to individual changes of the AES-key every 20 s 27 . In this case the consumed key rate is approximately 36 bytes s −1 and does not depend on the actual size of the plaintext message that is to be encrypted.…”

Practical photon number detection with electric field-modulated silicon avalanche photodiodes

“…M any schemes in quantum information processing [1][2][3] require that the photon number of a detected optical pulse is determined without error. For example, in quantum teleportation 4 and entanglement swapping 5 schemes used in quantum repeaters, a Bell state measurement applied upon two single photons arriving concurrently at a beam splitter requires number states N = 0, 1 or 2 to be distinguished in each detector.…”