Teng-Yun Chen, Jun Zhang, J. -C. Boileau, Xian-Min Jin, Bin Yang, Qiang Zhang, Tao Yang, R. Laflamme, Jian-Wei Pan
May 24, 2006·quant-ph·PDF We present an experimental realization of a robust quantum communication scheme [Phys. Rev. Lett. 93, 220501 (2004)] using pairs of photons entangled in polarization and time. Our method overcomes errors due to collective rotation of the polarization modes (e.g., birefringence in optical fiber or misalignment), is insensitive to the phase's fluctuation of the interferometer, and does not require any shared reference frame including time reference, except the need to label different photons. The practical robustness of the scheme is further shown by implementing a variation of the Bennett-Brassard 1984 quantum key distribution protocol over 1 km optical fiber.
Hui Liu, Wenyuan Wang, Kejin Wei, Xiao-Tian Fang, Li Li, Nai-Le Liu, Hao Liang, Si-Jie Zhang, Weijun Zhang, Hao Li, Lixing You, Zhen Wang, Hoi-Kwong Lo, Teng-Yun Chen, Feihu Xu, Jian-Wei Pan
Aug 26, 2018·quant-ph·PDF Measurement-device-independent quantum key distribution (MDI-QKD) can eliminate all detector side channels and it is practical with current technology. Previous implementations of MDI-QKD all use two symmetric channels with similar losses. However, the secret key rate is severely limited when different channels have different losses. Here we report the results of the first high-rate MDI-QKD experiment over $asymmetric$ channels. By using the recent 7-intensity optimization approach, we demonstrate $>$10x higher key rate than previous best-known protocols for MDI-QKD in the situation of large channel asymmetry, and extend the secure transmission distance by more than 20-50 km in standard telecom fiber. The results have moved MDI-QKD towards widespread applications in practical network settings, where the channel losses are asymmetric and user nodes could be dynamically added or deleted.
Yingqiu Mao, Yi-Zheng Zhen, Hui Liu, Mi Zou, Qi-Jie Tang, Si-Jie Zhang, Jian Wang, Hao Liang, Weijun Zhang, Hao Li, Lixing You, Zhen Wang, Li Li, Nai-Le Liu, Kai Chen, Teng-Yun Chen, Jian-Wei Pan
Jun 24, 2019·quant-ph·PDF Ensuring the non-entanglement-breaking (non-EB) property of quantum channels is crucial for the effective distribution and storage of quantum states. However, a practical method for direct and accurate certification of the non-EB feature is highly desirable. Here, we propose and verify a realistic source based measurement device independent certification of non-EB channels. Our method is resilient to repercussions on the certification from experimental conditions, such as multiphotons and imperfect state preparation, and can be implemented with information incomplete set. We achieve good agreement between experimental outcomes and theoretical predictions, which is validated by the expected results of the ideal semi-quantum signaling game, and accurately certify the non-EB channels. Furthermore, our approach is highly robust to effects from noise. Therefore, the proposed approach can be expected to play a significant role in the design and evaluation of realistic quantum channels.
Bi-Xiao Wang, Yingqiu Mao, Lei Shen, Lei Zhang, Xiao-Bo Lan, Dawei Ge, Yuyang Gao, Juhao Li, Yan-Lin Tang, Shi-Biao Tang, Jun Zhang, Teng-Yun Chen, Jian-Wei Pan
Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber, the average Raman noise in FMF is reduced by 86% at the same fiber-input power. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks
Hao-Tao Zhu, Yizhi Huang, Hui Liu, Pei Zeng, Mi Zou, Yunqi Dai, Shibiao Tang, Hao Li, Lixing You, Zhen Wang, Yu-Ao Chen, Xiongfeng Ma, Teng-Yun Chen, Jian-Wei Pan
Aug 11, 2022·quant-ph·PDF In the past two decades, quantum key distribution networks based on telecom fibers have been implemented on metropolitan and intercity scales. One of the bottlenecks lies in the exponential decay of the key rate with respect to the transmission distance. Recently proposed schemes mainly focus on achieving longer distances by creating a long-arm single-photon interferometer over two communication parties. Despite their advantageous performance over long communication distances, the requirement of phase-locking between two independent lasers is technically challenging. By adopting the recently-proposed mode-pairing idea, we realize high-performance quantum key distribution without global phase-locking. Using two independent off-the-shelf lasers, we show a quadratic key-rate improvement over the conventional measurement-device-independent schemes in the regime of metropolitan and intercity distances. For longer distances, we also boost the key rate performance by three orders of magnitude via 304 km commercial fiber and 407 km ultra-low-loss fiber. We expect this ready-to-implement high-performance scheme to be widely used in future intercity quantum communication networks.
Xiao-Tian Fang, Pei Zeng, Hui Liu, Mi Zou, Weijie Wu, Yan-Lin Tang, Ying-Jie Sheng, Yao Xiang, Weijun Zhang, Hao Li, Zhen Wang, Lixing You, Ming-Jun Li, Hao Chen, Yu-Ao Chen, Qiang Zhang, Cheng-Zhi Peng, Xiongfeng Ma, Teng-Yun Chen, Jian-Wei Pan
Quantum key distribution (QKD offers a long-term solution to establish information-theoretically secure keys between two distant users. In practice, with a careful characterization of quantum sources and the decoy-state method, measure-device-independent quantum key distribution (MDI-QKD) provides secure key distribution. While short-distance fibre-based QKD has already been available for real-life implementation, the bottleneck of practical QKD lies on the limited transmission distance. Due to photon losses in transmission, it was believed that the key generation rate is bounded by a linear function of the channel transmittance, $O(η)$, without a quantum repeater, which puts an upper bound on the maximal secure transmission distance. Interestingly, a new phase-encoding MDI-QKD scheme, named twin-field QKD, has been suggested to beat the linear bound, while another variant, named phase-matching quantum key distribution (PM-QKD), has been proven to have a quadratic key-rate improvement, $O(\sqrtη)$. In reality, however, the intrinsic optical mode mismatch of independent lasers, accompanied by phase fluctuation and drift, impedes the successful experimental implementation of the new schemes. Here, we solve this problem with the assistance of the laser injection technique and the phase post-compensation method. In the experiment, the key rate surpasses the linear key-rate bound via 302 km and 402 km commercial-fibre channels, achieving a key rate over 4 orders of magnitude higher than the existing results in literature. Furthermore, with a 502 km ultralow-loss fibre, our system yields a secret key rate of 0.118 bps. We expect this new type of QKD schemes to become a new standard for future QKD.
Ke Cui, Jian Wang, Hong-fei Zhang, Chun-li Luo, Ge Jin, Teng-yun Chen
Jan 10, 2013·quant-ph·PDF For high-speed quantum key distribution systems, error reconciliation is often the bottleneck affecting system performance. By exchanging common information through a public channel, the identical key can be generated on both communicating sides. However, the necessity to eliminate disclosed bits for security reasons lowers the final key rate. To improve this key rate, the amount of disclosed bits should be minimized. In addition, decreasing the time spent on error reconciliation also improves the key rate. In this paper we introduce a practical method for expeditious error reconciliation implemented in a Field Programmable Gate Array for a discrete variable quantum key distribution system, and illustrate the superiority of this method to other similar algorithms running on a PC. Experimental results demonstrate the rapidity of the proposed protocol.
Yan-Lin Tang, Hua-Lei Yin, Si-Jing Chen, Yang Liu, Wei-Jun Zhang, Xiao Jiang, Lu Zhang, Jian Wang, Li-Xing You, Jian-Yu Guan, Dong-Xu Yang, Zhen Wang, Hao Liang, Zhen Zhang, Nan Zhou, Xiongfeng Ma, Teng-Yun Chen, Qiang Zhang, Jian-Wei Pan
Aug 11, 2014·quant-ph·PDF A main type of obstacles of practical applications of quantum key distribution (QKD) network is various attacks on detection. Measurement-device-independent QKD (MDIQKD) protocol is immune to all these attacks and thus a strong candidate for network security. Recently, several proof-of-principle demonstrations of MDIQKD have been performed. Although novel, those experiments are implemented in the laboratory with secure key rates less than 0.1 bps. Besides, they need manual calibration frequently to maintain the system performance. These aspects render these demonstrations far from practicability. Thus, justification is extremely crucial for practical deployment into the field environment. Here, by developing an automatic feedback MDIQKD system operated at a high clock rate, we perform a field test via deployed fiber network of 30 km total length, achieving a 16.9 bps secure key rate. The result lays the foundation for a global quantum network which can shield from all the detection-side attacks.
Yang Liu, Teng-Yun Chen, Liu-Jun Wang, Hao Liang, Guo-Liang Shentu, Jian Wang, Ke Cui, Hua-Lei Yin, Nai-Le Liu, Li Li, Xiongfeng Ma, Jason S. Pelc, M. M. Fejer, Qiang Zhang, Jian-Wei Pan
Sep 27, 2012·quant-ph·PDF Throughout history, every advance in encryption has been defeated by advances in hacking with severe consequences. Quantum cryptography holds the promise to end this battle by offering unconditional security when ideal single-photon sources and detectors are employed. Unfortunately, ideal devices never exist in practice and device imperfections have become the targets of various attacks. By developing up-conversion single-photon detectors with high efficiency and low noise, we build up a measurement-device-independent quantum key distribution (MDI-QKD) system, which is immune to all hacking strategies on detection. Meanwhile, we employ the decoy-state method to defeat attacks on non-ideal source. By closing the loopholes in both source and detection, our practical system, which generates more than 25 kbit secure key over a 50-km fiber link, provides an ultimate solution for communication security.
Hua-Lei Yin, Yao Fu, Yan-Lin Tang, Yuan Li, Teng-Yun Chen, Zeng-Bing Chen
Jul 28, 2014·quant-ph·PDF We propose two quantum key distribution (QKD) protocols based on Bell's inequality, which can be considered as modified time-reversed E91 protocol. Similar to the measurement-device-independent quantum key distribution (MDI-QKD) protocol, the first scheme requires the assumption that Alice and Bob perfectly characterize the encoded quantum states. However, our second protocol does not require this assumption, which can defeat more known and unknown source-side attacks compared with the MDI-QKD. The two protocols are naturally immune to all hacking attacks with respect to detections. Therefore, the security of the two protocols can be proven based on the violation of Bell's inequality with measurement data under fair-sampling assumption. In our simulation, the results of both protocols show that long-distance quantum key distribution over 200 km remains secure with conventional lasers in the asymptotic-data case. We present a new technique to estimate the Bell's inequality violation, which can also be applied to other fields of quantum information processing.
Yuan Cao, Yu-Huai Li, Zhu Cao, Juan Yin, Yu-Ao Chen, Hua-Lei Yin, Teng-Yun Chen, Xiongfeng Ma, Cheng-Zhi Peng, Jian-Wei Pan
Mar 20, 2014·quant-ph·PDF Intuition from our everyday lives gives rise to the belief that information exchanged between remote parties is carried by physical particles. Surprisingly, in a recent theoretical study [Salih H, Li ZH, Al-Amri M, Zubairy MS (2013) Phys Rev Lett 110:170502], quantum mechanics was found to allow for communication, even without the actual transmission of physical particles. From the viewpoint of communication, this mystery stems from a (nonintuitive) fundamental concept in quantum mechanics wave-particle duality. All particles can be described fully by wave functions. To determine whether light appears in a channel, one refers to the amplitude of its wave function. However, in counterfactual communication, information is carried by the phase part of the wave function. Using a single-photon source, we experimentally demonstrate the counterfactual communication and successfully transfer a monochrome bitmap from one location to another by using a nested version of the quantum Zeno effect.
Qi-Chao Sun, Yang-Fan Jiang, Ya-li Mao, Li-Xing You, Wei Zhang, Wei-Jun Zhang, Xiao Jiang, Teng-Yun Chen, Hao Li, Yi-Dong Huang, Xian-Feng Chen, Zhen Wang, Jingyun Fan, Qiang Zhang, Jian-Wei Pan
Apr 13, 2017·quant-ph·PDF Realizing long distance entanglement swapping with independent sources in the real-world condition is important for both future quantum network and fundamental study of quantum theory. Currently, demonstration over a few of tens kilometer underground optical fiber has been achieved. However, future applications demand entanglement swapping over longer distance with more complicated environment. We exploit two independent 1-GHz-clock sequential time-bin entangled photon-pair sources, develop several automatic stability controls, and successfully implement a field test of entanglement swapping over more than 100-km optical fiber link including coiled, underground and suspended optical fibers. Our result verifies the feasibility of such technologies for long distance quantum network and for many interesting quantum information experiments.
Yan-Lin Tang, Hua-Lei Yin, Xiongfeng Ma, Chi-Hang Fred Fung, Yang Liu, Hai-Lin Yong, Teng-Yun Chen, Cheng-Zhi Peng, Zeng-Bing Chen, Jian-Wei Pan
Quantum key distribution (QKD) utilizes the laws of quantum mechanics to achieve information-theoretically secure key generation. This field is now approaching the stage of commercialization, but many practical QKD systems still suffer from security loopholes due to imperfect devices. In fact, practical attacks have successfully been demonstrated. Fortunately, most of them only exploit detection-side loopholes which are now closed by the recent idea of measurement-device-independent QKD. On the other hand, little attention is paid to the source which may still leave QKD systems insecure. In this work, we propose and demonstrate an attack that exploits a source-side loophole existing in qubit-based QKD systems using a weak coherent state source and decoy states. Specifically, by implementing a linear-optics unambiguous-state-discrimination measurement, we show that the security of a system without phase randomization --- which is a step assumed in conventional security analyses but sometimes neglected in practice --- can be compromised. We conclude that implementing phase randomization is essential to the security of decoy-state QKD systems under current security analyses.
Hui Liu, Zong-Wen Yu, Mi Zou, Yan-Lin Tang, Yong Zhao, Jun Zhang, Xiang-Bin Wang, Teng-Yun Chen, Jian-Wei Pan
May 23, 2019·quant-ph·PDF 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.
Teng-Yun Chen, Xiao Jiang, Shi-Biao Tang, Lei Zhou, Xiao Yuan, Hongyi Zhou, Jian Wang, Yang Liu, Luo-Kan Chen, Wei-Yue Liu, Hong-Fei Zhang, Ke Cui, Hao Liang, Xiao-Gang Li, Yingqiu Mao, Liu-Jun Wang, Si-Bo Feng, Qing Chen, Qiang Zhang, Li Li, Nai-Le Liu, Cheng-Zhi Peng, Xiongfeng Ma, Yong Zhao, Jian-Wei Pan
Sep 10, 2021·quant-ph·PDF Quantum key distribution (QKD) enables secure key exchanges between two remote users. The ultimate goal of secure communication is to establish a global quantum network. The existing field tests suggest that quantum networks are feasible. To achieve a practical quantum network, we need to overcome several challenges, including realising versatile topologies for large scales, simple network maintenance, extendable configuration, and robustness to node failures. To this end, we present a field operation of a quantum metropolitan-area network with 46 nodes and show that all these challenges can be overcome with cutting-edge quantum technologies. In particular, we realise different topological structures and continuously run the network for 31 months, by employing standard equipment for network maintenance with an extendable configuration. We realise QKD pairing and key management with a sophisticated key control center. In this implementation, the final keys have been used for secure communication such as real-time voice telephone, text messaging, and file transmission with one-time pad encryption, which can support 11 pairs of users to make audio calls simultaneously. Combined with inter-city quantum backbone and ground-satellite links, our metropolitan implementation paves the way toward a global quantum network.
Xiao-Hui Bao, Teng-Yun Chen, Qiang Zhang, Jian Yang, Han Zhang, Tao Yang, Jian-Wei Pan
Oct 21, 2006·quant-ph·PDF We present and experimentally demonstrate a novel optical nondestructive controlled-NOT gate without using entangled ancilla. With much fewer measurements compared with quantum process tomography, we get a good estimation of the gate fidelity. The result shows a great improvement compared with previous experiments. Moreover, we also show that quantum parallelism is achieved in our gate and the performance of the gate can not be reproduced by local operations and classical communications.
Qi-Chao Sun, Ya-Li Mao, Yang-Fan Jiang, Qi Zhao, Sijing Chen, Wei Zhang, Weijun Zhang, Xiao Jiang, Teng-Yun Chen, Lixing You, Li Li, Yidong Huang, Xianfeng Chen, Zhen Wang, Xiongfeng Ma, Qiang Zhang, Jian-Wei Pan
Jun 23, 2016·quant-ph·PDF Teleportation of an entangled state, known as entanglement swapping, plays an essential role in quantum communication and network.Here we report a field-test entanglement swapping experiment with two independent telecommunication band entangled photon-pair sources over the optical fibre network of Hefei city. The two sources are located at two nodes 12 km apart and the Bell-state measurement is performed in a third location which is connected to the two source nodes with 14.7 km and 10.6 km optical fibres. An average visibility of 79.9+/-4.8% is observed in our experiment, which is high enough to infer a violation of Bell inequality. With the entanglement swapping setup, we demonstrate a source independent quantum key distribution, which is also immune to any attack against detection in the measurement site.
Jian-Yu Guan, Feihu Xu, Hua-Lei Yin, Yuan Li, Wei-Jun Zhang, Si-Jing Chen, Xiao-Yan Yang, Li Li, Li-Xing You, Teng-Yun Chen, Zhen Wang, Qiang Zhang, Jian-Wei Pan
Quantum communication has historically been at the forefront of advancements, from fundamental tests of quantum physics to utilizing the quantum-mechanical properties of physical systems for practical applications. In the field of communication complexity, quantum communication allows the advantage of an exponential reduction in the information transmitted over classical communication to accomplish distributed computational tasks. However, to date, demonstrating this advantage in a practical setting continues to be a central challenge. Here, we report an experimental demonstration of a quantum fingerprinting protocol that for the first time surpasses the ultimate classical limit to transmitted information. Ultra-low noise superconducting single-photon detectors and a stable fibre-based Sagnac interferometer are used to implement a quantum fingerprinting system that is capable of transmitting less information than the classical proven lower bound over 20 km standard telecom fibre for input sizes of up to two Gbits. The results pave the way for experimentally exploring the advanced features of quantum communication and open a new window of opportunity for research in communication complexity and testing the foundations of physics.
Hua-Lei Yin, Yao Fu, Hui Liu, Qi-Jie Tang, Jian Wang, Li-Xing You, Wei-Jun Zhang, Si-Jing Chen, Zhen Wang, Qiang Zhang, Teng-Yun Chen, Zeng-Bing Chen, Jian-Wei Pan
Quantum digital signature (QDS) is an approach to guarantee the nonrepudiation, unforgeability and transferability of a signature with the information-theoretical security. All previous experimental realizations of QDS relied on an unrealistic assumption of secure channels and the longest distance is only several kilometers. Here, we have experimentally demonstrated a recently proposed QDS protocol without any secure channel. Exploiting the decoy state modulation, we have successfully signed one bit message through up to 102 km optical fiber. Furthermore, we continuously run the system to sign the longer message "USTC" with 32 bit at the distance of 51 km. Our results pave the way towards the practical application of QDS.
Yao Fu, Hua-Lei Yin, Teng-Yun Chen, Zeng-Bing Chen
The Greenberger-Horne-Zeilinger (GHZ) entanglement, originally introduced to uncover the extreme violation of local realism against quantum mechanics, is an important resource for multiparty quantum communication tasks. But the low intensity and fragility of the GHZ entanglement source in current conditions have made the practical applications of these multiparty tasks an experimental challenge. Here we propose a feasible scheme for practically distributing the post-selected GHZ entanglement over a distance of more than 100 km for experimentally accessible parameter regimes. Combining the decoy-state and measurement-device-independent protocols for quantum key distribution, we anticipate that our proposal suggests an important avenue for practical multiparty quantum communication.