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Differential-phase-shift quantum key distribution using heralded narrow-band single photons

Chang Liu, Shanchao Zhang, Luwei Zhao, Peng Chen, C. -H. F. Fung, H. F. Chau, M. M. T. Loy, Shengwang Du

Published Apr 10, 2013• 23 citations
Publisher

Abstract

We demonstrate the first proof of principle differential phase shift (DPS) quantum key distribution (QKD) using narrow-band heralded single photons with amplitude-phase modulations. In the 3-pulse case, we obtain a quantum bit error rate (QBER) as low as 3.06% which meets the unconditional security requirement. As we increase the pulse number up to 15, the key creation efficiency approaches 93.4%, but with a cost of increasing the QBER. Our result suggests that narrow-band single photons maybe a promising source for the DPS-QKD protocol.

DOI
10.1364/oe.21.009505

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Sep 9, 2007•3 citations
We demonstrate the first proof of principle differential phase shift (DPS) quantum key distribution (QKD) using narrow-band heralded single photons with amplitude-phase modulations. In the 3-pulse case, we obtain a quantum bit error rate (QBER) as low as 3.06% which meets the unconditional security requirement. As we increase the pulse number up to 15, the key creation efficiency approaches 93.4%, but with a cost of increasing the QBER. Our result suggests that narrow-band single photons maybe a promising source for the DPS-QKD protocol.
In this Letter, we prove the unconditional security of the single-photon differential phase shift quantum key distribution (DPS-QKD) protocol, based on the conversion to an equivalent entanglement-based protocol. We estimate the upper bound of the phase error rate from the bit error rate, and show that the DPS-QKD protocol can generate an unconditionally secure key when the bit error rate is not greater than 4.12%. This proof is the first step to the unconditional security proof of a coherent state DPS-QKD.
Differential phase-shift (DPS) quantum key distribution (QKD) is a unique QKD protocol that is different from traditional ones, featuring simplicity and practicality. In this work, we simulated the DPS-QKD experiment conducted by (Liu et al., 2013), using OptiSystem 7. To the best of our knowledge, this is the first simulation work on DPS-QKD using a single photon source.We used a random number generator to get the phase modulation pattern of N=5, 7,9,11 and 13, while for the 3 and 15 pulse cases, the pattern adopted in the experiment was used. When the number of pulse (N) was 3, a quantum bit error rate (QBER) of 3.0%, which is lower than the minimum QBER of 4.12% required for unconditional security, was obtained. The key creation efficiency increases with the increase in the number of pulse up to 15, as it reaches 93.4% but at the expense of the increment in QBER. The result of our simulation is, on some aspect, in agreement with the experimental result. However, we were able to extend the transmission distance from 3 meter, as in the experiment, to 10 meter. The coincidence count obtained was also in total agreement with the one obtained from the experiment. The result of the average QBER indicated that increase in the pulse number N causes the QBER to raise up due to longer rise and fall time of phase modulation step which affect the MZ inference. Therefore, we suggest using a faster waveform generator with shorter rise and fall times will remarkably lower the QBER. Extending the transmission coverage to a longer distance while, at the same time reducing the QBER with full unconditional security will part of the future research.
We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors of 2 and 3, respectively. For N(≥3)-period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum-memory-based long-distance fiber communication systems.
Differential-phase-shift (DPS) quantum key distribution (QKD) is one of the major QKD protocols that can be implemented with a simple setup using a laser source and a passive detection unit. Recently, an information-theoretic security proof of this protocol was established by Mizutani et al. [npj Quantum Inf. 5, 87 (2019)], assuming an infinitely large number of emitted pulses. To implement the DPS protocol in a real-life world, it is indispensable to analyze the security with the finite number of emitted pulses. The extension of the security proof to the finite-size regime requires the accommodation of the statistical fluctuations to determine the amount of privacy amplification. In doing so, Azuma's inequality is often employed, but unfortunately we show that in the case of the DPS protocol, this results in a substantially low key rate. This low key rate is due to a loose estimation of the sum of probabilities regarding three-photon emission whose probability of occurrence is very small. The main contribution of our work is to show that this obstacle can be overcome by exploiting the recently found novel concentration inequality, Kato's inequality. As a result, the key rate of the DPS protocol is drastically improved. For instance, assuming typical experimental parameters, a 3-Mbit secret key can be generated over 77 km for 8.3 hours, which shows the feasibility of DPS QKD under a realistic setup.
A novel type of quantum key distribution (QKD) protocol, called DPS (differential-phase-shift) QKD, was proposed several years ago. A sender transmits a highly-attenuated coherent pulse train with {0, π} phase, and a receiver receives it with a one-bit delay Mach-Zehnder interferometer followed by photon detectors. A secret key is created from photon detection events, whose security is based on the fact that an eavesdropper cannot perfectly measure the phase information of a highly-attenuated coherent pulse train. This protocol has some features of simple setup, potential for a high key creation rate, and robustness against photon-number-splitting attack. This paper overviews DPS-QKD. The operation mechanism is described, and then some experimental efforts are introduced, featuring use of a glass waveguide Mach-Zehnder interferometer and advanced single-photon detectors. The highest key rate and the longest distance have been achieved with the DPS-QKD protocol. Some modified schemes are also presented, including that utilizing quantum entanglement, that using decoy pulses, and that using macroscopic coherent light.