© 2017 IOP Publishing Ltd. We report a new apparatus for the study of two-species quantum degenerate mixture of ⁴¹ K and ⁶ Li atoms. We develop and combine several advanced cooling techniques to achieve both a large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of an extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for ⁴¹ K atoms while the ⁶ Li atoms are sympathetically cooled in an optically plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the ⁴¹ K and ⁶ Li atoms. The Bose-Einstein condensate of ⁴¹ K has 1.4 × 10 ⁵ atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of ⁶ Li has a total atom number of 5.4 × 10 ⁵ at 0.25 Fermi temperature.

Wu Yu-Ping;Yao Xing-Can;Chen Hao-Ze;Liu Xiang-Pei;Wang Xiao-Qiong;Chen Yu-Ao;Pan Jian-Wei

Journal of Physics B Atomic Molecular and Optical Physics

2017

© 2017 American Physical Society. Boson sampling is a problem strongly believed to be intractable for classical computers, but can be naturally solved on a specialized photonic quantum simulator. Here, we implement the first time-bin-encoded boson sampling using a highly indistinguishable (∼94%) single-photon source based on a single quantum-dot-micropillar device. The protocol requires only one single-photon source, two detectors, and a loop-based interferometer for an arbitrary number of photons. The single-photon pulse train is time-bin encoded and deterministically injected into an electrically programmable multimode network. The observed three- and four-photon boson sampling rates are 18.8 and 0.2 Hz, respectively, which are more than 100 times faster than previous experiments based on parametric down-conversion.

He Yu;Ding X.;Su Z. E.;Huang H. L.;Qin J.;Wang C.;Chen C.;Wang H.;He Y. M.;Wang X. L.;H\u00f6fling S.;Lu Chao-Yang;Pan Jian-Wei;Unsleber S.;Schneider C.;Kamp M.;Zhang W. J.;Chen S. J.;You L. X.;Wang Z.

Physical Review Letters

2017

© 2017 American Physical Society. Superconducting quantum circuits are a promising candidate for building scalable quantum computers. Here, we use a four-qubit superconducting quantum processor to solve a two-dimensional system of linear equations based on a quantum algorithm proposed by Harrow, Hassidim, and Lloyd [Phys. Rev. Lett. 103, 150502 (2009)PRLTAO0031-900710.1103/PhysRevLett.103.150502], which promises an exponential speedup over classical algorithms under certain circumstances. We benchmark the solver with quantum inputs and outputs, and characterize it by nontrace-preserving quantum process tomography, which yields a process fidelity of 0.837±0.006. Our results highlight the potential of superconducting quantum circuits for applications in solving large-scale linear systems, a ubiquitous task in science and engineering.

Zheng Yarui;Deng Hui;Huang Keqiang;Wu Yulin;Yan Zhiguang;Zheng Dongning;Lu Li;Zhu Xiaobo;Song Chao;Liu Wuxin;Guo Qiujiang;Zhang Libo;Xu Da;Wang H.;Chen Ming-Cheng;Xia Benxiang;Pan Jian-Wei;Lu Chao-Yang

Physical Review Letters

2017

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometres, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate. Satellite-based QKD has the potential to help to establish a global-scale quantum network, owing to the negligible photon loss and decoherence experienced in empty space. Here we report the development and launch of a low-Earth-orbit satellite for implementing decoy-state QKD - a form of QKD that uses weak coherent pulses at high channel loss and is secure because photon-number-splitting eavesdropping can be detected. We achieve a kilohertz key rate from the satellite to the ground over a distance of up to 1,200 kilometres. This key rate is around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. The establishment of a reliable and efficient space-to-ground link for quantum-state transmission paves the way to global-scale quantum networks.

Liao Sheng Kai;Cai Wen Qi;Liu Wei Yue;Li Yang;Ren Ji Gang;Yin Juan;Shen Qi;Cao Yuan;Li Zheng Ping;Li Feng Zhi;Chen Xia Wei;Sun Li Hua

Nature

2017

Processing of digital images is continuously gaining in volume and relevance, with concomitant demands on data storage, transmission, and processing power. Encoding the image information in quantum-mechanical systems instead of classical ones and replacing classical with quantum information processing may alleviate some of these challenges. By encoding and processing the image information in quantum-mechanical systems, we here demonstrate the framework of quantum image processing, where a pure quantum state encodes the image information: we encode the pixel values in the probability amplitudes and the pixel positions in the computational basis states. Our quantum image representation reduces the required number of qubits compared to existing implementations, and we present image processing algorithms that provide exponential speed-up over their classical counterparts. For the commonly used task of detecting the edge of an image, we propose and implement a quantum algorithm that completes the task with only one single-qubit operation, independent of the size of the image. This demonstrates the potential of quantum image processing for highly efficient image and video processing in the big data era.

Yao Xi-Wei;Wang Hengyan;Pan Jian;Peng Xinhua;Liao Zeyang;Chen Ming-Cheng;Li Jun;Luo Zhihuang;Zhang Kechao;Lin Xingcheng;Wang Zhehui;Zheng Wenqiang;Li Jianzhong;Zhao Meisheng;Suter Dieter

Physical Review X

2017

© 2017 American Physical Society. Here we report on the production and tomography of genuinely entangled Greenberger-Horne-Zeilinger states with up to ten qubits connecting to a bus resonator in a superconducting circuit, where the resonator-mediated qubit-qubit interactions are used to controllably entangle multiple qubits and to operate on different pairs of qubits in parallel. The resulting 10-qubit density matrix is probed by quantum state tomography, with a fidelity of 0.668±0.025. Our results demonstrate the largest entanglement created so far in solid-state architectures and pave the way to large-scale quantum computation.

Song Chao;Xu Kai;Liu Wuxin;Guo Qiujiang;Zhang Libo;Zhang Pengfei;Xu Da;Wang H.;Zhu Xiaobo;Chen Y. A.;Lu C. Y.;Pan Jian-Wei;Yang Chui-Ping;Zheng Shi-Biao;Deng Hui;Huang Keqiang;Zheng Dongning;Xie Qiwei;Han Siyuan

Physical Review Letters

2017

© 2017 American Physical Society. We report on entanglement-based quantum key distribution between a low-Earth-orbit satellite equipped with a space borne entangled-photon source and a ground observatory. One of the entangled photons is measured locally at the satellite, and the other one is sent via a down link to the receiver in the Delingha ground station. The link attenuation is measured to vary from 29 dB at 530 km to 36 dB at 1000 km. We observe that the two-photon entanglement survives after being distributed between the satellite and the ground, with a measured state fidelity of ≥0.86. We then perform the entanglement-based quantum key distribution protocol and obtain an average final key rate of 3.5 bits/s at the distance range of 530-1000 km.

Yin Juan;Cao Yuan;Li Yu-Huai;Ren Ji-Gang;Liao Sheng-Kai;Cai Wen-Qi;Liu Wei-Yue;Li Bo;Dai Hui;Li Li;Zhang Qiang;Liu Nai-Le;Chen Yu-Ao;Lu Chao-Yang;Peng Cheng-Zhi;Pan Jian-Wei;Zhang Liang;Shu Rong;Wang Jian-Yu;Li Ming;Huang Yong-Mei;Deng Lei

Physical Review Letters

2017

© 2018 American Physical Society. Quantum entanglement was termed "spooky action at a distance" in the well-known paper by Einstein, Podolsky, and Rosen. Entanglement is expected to be distributed over longer and longer distances in both practical applications and fundamental research into the principles of nature. Here, we present a proposal for distributing entangled photon pairs between Earth and the Moon using a Lagrangian point at a distance of 1.28 light seconds. One of the most fascinating features in this long-distance distribution of entanglement is as follows. One can perform the Bell test with human supplying the random measurement settings and recording the results while still maintaining spacelike intervals. To realize a proof-of-principle experiment, we develop an entangled photon source with 1 GHz generation rate, about 2 orders of magnitude higher than previous results. Violation of Bell's inequality was observed under a total simulated loss of 103 dB with measurement settings chosen by two experimenters. This demonstrates the feasibility of such long-distance Bell test over extremely high-loss channels, paving the way for one of the ultimate tests of the foundations of quantum mechanics.

Cao Yuan;Li Yu-Huai;Li Zheng-Ping;Shen Qi;Liao Sheng-Kai;Ren Ji-Gang;Yin Juan;Chen Yu-Ao;Peng Cheng-Zhi;Pan Jian-Wei;Zou Wen-Jie

Physical Review Letters

2018

© 2018 Macmillan Publishers Ltd., part of Springer Nature. A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism ¹, in which the properties of the physical world are independent of our observation of them and no signal travels faster than light. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings ^2,3 . Although technology can satisfy the first two of these requirements ^4-7, the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human 'free will' could be used rigorously to ensure unpredictability in Bell tests ⁸ . Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology ⁹ . The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons ^5,6, single atoms ⁷, atomic ensembles ¹⁰ and superconducting devices ¹¹ . Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bipartite and tripartite ¹² scenarios. Project outcomes include closing the 'freedom-of-choice loophole' (the possibility that the setting choices are influenced by 'hidden variables' to correlate with the particle properties ¹³ ), the utilization of video-game methods ¹⁴ for rapid collection of human-generated randomness, and the use of networking techniques for global participation in experimental science.

Abellán C.;Acín A.;Beduini F. A.;Carrasco S.;Cavalcanti D.;De Riedmatten H.;Farrera P.;García-Matos M.;Heinze G.;Hirschmann A.;Jiménez O.;Lenhard A.

Nature

2018

© 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Creating large-scale entanglement lies at the heart of many quantum information processing protocols and the investigation of fundamental physics. For multipartite quantum systems, it is crucial to identify not only the presence of entanglement but also its detailed structure. This is because in a generic experimental situation with sufficiently many subsystems involved, the production of so-called genuine multipartite entanglement remains a formidable challenge. Consequently, focusing exclusively on the identification of this strongest type of entanglement may result in an all or nothing situation where some inherently quantum aspects of the resource are overlooked. On the contrary, even if the system is not genuinely multipartite entangled, there may still be many-body entanglement present in the system. An identification of the entanglement structure may thus provide us with a hint about where imperfections in the setup may occur, as well as where we can identify groups of subsystems that can still exhibit strong quantum-information-processing capabilities. However, there is no known efficient methods to identify the underlying entanglement structure. Here, we propose two complementary families of witnesses for the identification of such structures. They are based, respectively, on the detection of entanglement intactness and entanglement depth, each applicable to an arbitrary number of subsystems and whose evaluation requires only the implementation of solely two local measurements. Our method is also robust against noises and other imperfections, as reflected by our experimental implementation of these tools to verify the entanglement structure of five different eight-photon entangled states. In particular, we demonstrate how their entanglement structure can be precisely and systematically inferred from the experimental measurement of these witnesses. In achieving this goal, we also illustrate how the same set of data can be classically postprocessed to learn the most about the measured system.

Lu He;Li Zheng-Da;Yin Xu-Fei;Yuan Xiao;Chen Luo-Kan;Li Li;Liu Nai-Le;Peng Cheng-Zhi;Chen Yu-Ao;Pan Jian-Wei;Zhao Qi;Ma Xiongfeng;Hung Jui-Chen;Liang Yeong-Cherng

Physical Review X

2018