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Zong-Wen Yu

Publications and source records attributed to Zong-Wen Yu.

34 records · Page 2Linked to original sources
arXiv2019

Experimental 4-intensity decoy-state quantum key distribution with asymmetric basis detector efficiency

The decoy-state method has been developed rapidly in quantum key distribution (QKD) since it is immune to photon-number splitting attacks. However, two basis detector efficiency asymmetry, which exists in realistic scenarios, has been ignored in the prior results. By using the recent 4-intensity decoy-state optimization protocol, we report the first implementation of high-rate QKD with asymmetric basis detector efficiency, demonstrating 1.9 to 33.2 times higher key rate than previous protocols in the situation of large basis detector efficiency asymmetry. The results ruled out an implicitly assumption in QKD that the efficiency of Z basis and X basis are restricted to be same. This work paves the way towards a more practical QKD setting.

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arXiv2019

Unconditional security of sending or not sending twin-field quantum key distribution with finite pulses

The Sending-or-Not-Sending protocol of the twin-field quantum key distribution (TF-QKD) has its advantage of unconditional security proof under any coherent attack and fault tolerance to large misalignment error. So far this is the only coherent-state based TF-QKD protocol that has considered finite-key effect, the statistical fluctuations. Here we consider the complete finite-key effects for the protocol and we show by numerical simulation that the protocol with typical finite number of pulses in practice can produce unconditional secure final key under general attack, including all coherent attacks. It can exceed the secure distance of 500 $km$ in typical finite number of pulses in practice even with a large misalignment error.

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arXiv2018

Encoding-side-channel-free and measurement-device-independent quantum key distribution

We present a simple protocol where Alice and Bob only needs sending out a coherent state or not-sending out a coherent state to Charlie. There is no bases switching. We show that this protocol is both encoding-state-side-channel free to the source part and measurement-device-independent. We don't have to control exactly the whole space state of the light pulse, which is an impossible task in practice. The protocol is immune to all adverse due to encoding-state imperfections in side-channel space such as the photon frequency spectrum, emission time, propagation direction, spatial angular moment, and so on. Numerical simulation shows that our scheme can reach a side-channel-free result for quantum key distribution over a distance longer than 200 km given the single-photon-interference misalignment error rate of $20\%$.

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arXiv2018

Sending or not sending: twin-field quantum key distribution with large misalignment error

Based on the novel idea of twin-field quantum key distribution, we present a sending-or-not-sending twin-field fault tolerant quantum key distribution protocol. Our protocol can access a secure distance longer than 700 km even though the misalignment error rate is $15\%$. In the case of zero alignment error, our protocol can exceeds a secure distance of 800 km. Thanks to the novel idea of TF-QKD !

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arXiv2018

Sending-or-not twin-field quantum key distribution in practice

We present results of practical sending-or-not quantum key distribution. In real-life implementations, we need consider the following three requirements, a few different intensities rather than infinite number of different intensities, a phase slice of appropriate size rather than infinitely small size and the statistical fluctuations. We first show the decoy-state method with only a few different intensities and a phase slice of appropriate size. We then give a statistical fluctuation analysis for the decoy-state method. Numerical simulation shows that, the performance of our method is comparable to the asymptotic case for which the key size is large enough. Our results show that practical implementations of the sending-or-not quantum key distribution can be both secure and efficient.

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arXiv2018

Practical scheme for long distance side-channel-free quantum key distribution with weak coherent states only

We show that a side-channel-free (SCF) source does not have to be an ideal source by introducing the idea of mapping from ideal source. We propose a 3-state no-touch protocol for quantum key distribution (QKD) where Alice and Bob does not modulate any light sent out, the only thing the do is to send (or not send, in sending-or-not protocol). The reference light are from independent Lasers. We show that, the protocol is side-channel-free (i.e., both source side channel free and measurement device independent) and there is no modulation to the weak beams for QKD coding, except for sending or not sending. Calculation shows that one can reach a side-channel-free secure distance over 300 km using only coherent-state source. We use worst-case analysis which takes no limitation to the channel or detection loss for security. Our protocol is immune to all adverse due to side channels such as the photon frequency spectrum, emission time, propagation direction, spatial angular moment, and so on. Numerical simulations show that our scheme can reach a side-channel-free result for quantum key distribution over a distance longer than 200 km given the single-photon-interference misalignment error rate of 30%, and a distance longer than 300 km given the single-photon-interference misalignment error rate of 10%. Our no-touch idea can also apply to phase-coding twin-field QKD protocols. The no-touch idea also applies to twin-field QKD with phase coding.

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arXiv2017

Measurement-device-independent quantum key distribution with source state errors and statistical fluctuation

We show how to calculate the secure final key rate in the four-intensity decoy-state MDI-QKD protocol with both source errors and statistical fluctuations with a certain failure probability. Our results rely only on the range of only a few parameters in the source state. All imperfections in this protocol have been taken into consideration without any unverifiable error patterns.

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arXiv2016

Measurement device independent quantum key distribution over 404 km optical fibre

Quantum key distribution (QKD) can provide unconditional secure communication between two distant parties. Although the significance of QKD is undisputed, its feasibility has been questioned because of certain limitations in the practical application of real-life QKD systems. It is a common belief the lack of perfect single-photon source and the existence of detection loss will handicap the feasibility of QKD by creating security loopholes and distance limitations. The measurement device independent QKD (MDIQKD) with decoy-state method removes the security threats from both the imperfect single-photon source and the detection loss. Lengthening the distance and improving the key rate of QKD with such a superior method is thus the central issue in the practical application of QKD. Here, we report the results of MDIQKD over 404 km of ultralow-loss optical fibre and 311 km of standard optical fibre by employing an optimized four-intensity decoy-state method. This record-breaking implementation of MDIQKD method not only provides a new distance record for both MDIQKD and all types of QKD systems, more significantly, it achieves a distance that the traditional BB84 QKD would not be able to achieve with the same detection devices even with ideal single-phone sources. For the first time, our work demonstrates that with the MDIQKD method, imperfect devices can achieve better results than what ideal sources could have achieved. This work represents a significant step towards proving and developing a feasible long-distance QKD.

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arXiv2015

Improved statistical fluctuation analysis for measurement-device-independent quantum key distribution with three-intensity decoy-state method

We present an improved statistical fluctuation analysis for measurement device independent quantum key distribution with three-intensity decoy-state method. Taking the statistical fluctuations for different sources jointly, we present more tightened formulas for some key quantities used in calculating the secure final key. Numerical simulation shows that, given the total number of pulses $10^{12}$, our method improves the key rate by about 97\% for a distance of 50kms compared with the result given by Xu., et al. (Phys. Rev. A 89, 052333); and improves the key rate by $146\%$ for a distance of 100kms compared with the result from full optimization of all parameters but treating the statistical fluctuations traditionally, i.e., treating the fluctuations for different sources separately.

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arXiv2013

Decoy state method for measurement device independent quantum key distribution with different intensities in only one basis

We show that the three-intensity protocol for measurement device independent quantum key distribution (MDI QKD) can be done with different light intensities in {\em only one} basis. Given the fact that the exact values yields of single-photon pairs in the $X$ and $Z$ bases must be the same, if we have lower bound of the value in one basis, we can also use this as the lower bound in another basis. Since in the existing set-up for MDI-QKD, the yield of sources in different bases are normally different, therefore our method can improve the key rate drastically if we choose to only use the lower bound of yield of single-photon pairs in the advantageous basis. Moreover, since our proposal here uses fewer intensities of light, the probability of intensity mismatch will be smaller than the existing protocols do. This will further improve the advantage of our method. The advantage of using Z basis or X basis of our method is studied and significant improvement of key rates are numerically demonstrated.

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arXiv2013

Efficient tomography of quantum-optical Gaussian processes probed with a few coherent states

An arbitrary quantum-optical process (channel) can be completely characterized by probing it with coherent states using the recently developed coherent-state quantum process tomography (QPT) [Lobino et al., Science 322, 563 (2008)]. In general, precise QPT is possible if an infinite set of probes is available. Thus, realistic QPT of infinite-dimensional systems is approximate due to a finite experimentally-feasible set of coherent states and its related energy-cut-off approximation. We show with explicit formulas that one can completely identify a quantum-optical Gaussian process just with a few different coherent states without approximations like the energy cut-off. For tomography of multimode processes, our method exponentially reduces the number of different test states, compared with existing methods.

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arXiv2010

Entanglement distribution maximization over one-side Gaussian noisy channel

The optimization of entanglement evolution for two-mode Gaussian pure states under one-side Gaussian map is studied. Even there isn't complete information about the one-side Gaussian noisy channel, one can still maximize the entanglement distribution by testing the channel with only two specific states.

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arXiv2008

Unified Approach to Universal Cloning and Phase-Covariant Cloning

We analyze the problem of approximate quantum cloning when the quantum state is between two latitudes on the Bloch's sphere. We present an analytical formula for the optimized 1-to-2 cloning. The formula unifies the universal quantum cloning (UQCM) and the phase covariant quantum cloning.

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