Tools for the performance optimization of single-photon quantum key distribution

Abstract

Quantum light sources emitting triggered single photons or entangled photon pairs have the potential to boost the performance of quantum key distribution (QKD) systems. Proof-of-principle experiments affirmed these prospects, but further efforts are necessary to push this field beyond its current status. In this work, we show that temporal filtering of single-photon pulses enables a performance optimization of QKD systems implemented with realistic quantum light sources, both in experiment and simulations. To this end, we analyze the influence of temporal filtering of sub-Poissonian single-photon pulses on the expected secret key fraction, the quantum bit error ratio, and the tolerable channel losses. For this purpose, we developed a basic QKD testbed comprising a triggered solid-state single-photon source and a receiver module designed for fourstate polarization coding via the BB84 protocol. Furthermore, we demonstrate real-time security monitoring by analyzing the photon statistics, in terms of g (2) (0), inside the quantum channel by correlating the photon flux recorded at the four ports of our receiver. Our findings are useful for the certification of QKD and can be applied and further extended for the optimization of various implementations of quantum communication based on sub-Poissonian quantum light sources, including device-independent schemes of QKD as well as quantum repeaters. Our work represents an important contribution towards the development of QKD-secured communication networks based on quantum light sources.

Quantum key distribution with entangled photons generated on demand by a quantum dot

“…The noise is due to dark counts (on average 250 cps), afterpulsing of the detectors, and, after the free-space optical link, undesired photons from the reference laser used for beam stabilization. The latter effects lead to an increase in the value of , as estimated during the QKD by analyzing the coincidences among the detectors operated by one communicating party ( 24 ), to 0.02 for the SMF link and 0.038 for the free-space channel.…”

“…So far, the application of QD-based light sources has focused on single-photon prepare-and-measure protocols, exploring polarization ( 7 , 19 ) and time-bin encoding ( 20 ), electrical ( 21 ) and optical pumping, and laboratory tests and field demonstrations ( 22 ), possibly even with spectral multiplexing ( 23 ). Most recent works foresee even the possibility to outperform state-of-the-art solutions based on the decoy-state protocol and weak coherent pulse sources ( 24 ). One pioneering demonstration of the entanglement-based BBM92 protocol has been realized using an entangled light-emitting diode ( 25 ).…”

Quantum cryptography with highly entangled photons from semiconductor quantum dots

“…For the key generation, we include all photons from the QD by choosing a time bin of 1 ns [the same as used for determining g (2) (0)], which is about four times as long as X decay time. This excludes the largest amount of background photons from ambient light but includes about 97% of the photons from the QD and on April 22, 2021 http://advances.sciencemag.org/ Downloaded from therefore does not temporally filter the signal appreciably [which, however, can be done in applications supporting high time resolution (44)]. Figure 3A shows the raw key rate, which has an average of 135 bits/s over a time span of 13 hours.…”

Distinguishing intrinsic photon correlations from external noise with frequency-resolved homodyne detection

“…The correlation measurements outlined above usually require quite long integration times to produce a single value of , which results e.g. in integration times of minutes for state of the art real-time monitoring of quantum light sources in quantum key distribution 4 . Accordingly, it is very difficult to distinguish between intrinsic and external noise contributions to in such experiments.…”

“…For purposes of characterization, they are fundamental for tasks as different as determining the single photon purity of single photon sources 1 , monitoring the stable operation of lasers 2 and investigating diffusion via fluorescence correlation spectroscopy 3 . For communications protocols, they play a prominent role in monitoring quantum light sources to enable secret key distillation 4 as well as in advanced protocols that merge chaos communication and ghost imaging 5 . Especially the latter applications require a constant real time monitoring of photon correlations.…”