Zhi Ma

Quantum random number generator (QRNG) relies on the intrinsic randomness of quantum mechanics to produce true random numbers which are important in many fields. QRNGs with semiconductor light source have attracted a lot of attention due to their operational simplicity and high generation rate. However, the temperature of light source may vary due to imperfect devices and other factors. There is still a lack of study on the effects of temperature variations on the security of practical QRNG. We fill this gap by presenting a numerical method for studying the effects of temperature increase on the super-luminescent emitting diode (SLED) based QRNG and propose some strategies toward robust QRNG against temperature increase.

The finite-key security of the standard three-intensity decoy-state quantum key distribution QKD) protocol in the presence of information leakage has been analyzed (Wang et al. in New J Phys 20:083027, 2018). On the other hand, the 1-decoy state QKD protocol has been proved to be able to achieve higher secret key rate than the three-intensity decoy-state QKD protocol in the finite-key regime by using only two different intensity settings (Davide et al. in Appl Phys Lett 112:171104, 2018). In this work, we analyze the finite-key security of the 1-decoy state QKD protocol with a leaky intensity modulator, which is used to generate the decoy state. In particular, we simulate the secret key rate under three practical cases of Trojan-horse attacks. Our simulation results demonstrate that the 1-decoy state QKD protocol can be secure over long distances within a reasonable time frame given that the intensity modulator is sufficiently isolated. By comparing the simulation results to those presented in Wang et al. (2018), we find that, as expected, the 1-decoy state QKD protocol is more robust against information leakage from the intensity modulator for all achievable distances.

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all the detection attacks, thus when it is combined with the decoy state method, the final key is unconditional security, even the practical weak coherent source are used by Alice and Bob. However, until now, the analysis of decoy state MDI-QKD with weak coherent state is incomplete. In this paper, we derive, with only vacuum+weak decoy state, some tight formulas to estimate the lower bound of yield and the upper bound of error rate for the fraction of signals in which both Alice and Bob send single photon pulse to the untrusted third party Charlie. The numerical simulations show that our method with only vacuum+weak decoy state can asymptotically approach to the theoretical limit of the infinite number of decoy states. Furthermore, the statistical fluctuation due to the finite length of date is also considered based on the standard statistical analysis.

Reconciliation is an important step to correct errors in Quantum Key Distribution (QKD). In QKD, after comparing basis, two legitimate parties possess two correlative keys which have some difference and they could obtain identical keys through reconciliation. In our paper, we present a new rate compatible reconciliation scheme based on Row Combining with Edge Variation (RCEV) Low Density Parity Check (LDPC) codes which could change code rate adaptively in noisy channel where error rate may changes with time. Our scheme is easy to implement and could get good efficiency compared to existing schemes. Meanwhile, due to the inherent structure we use, the new scheme not only save memory space remarkably but also simplify the decoder architecture and accelerate the decoding.