Showing 1–50 of 74 results for author: Xiang, G

Lensing and enhanced single atom detection via a single-pixel nanostructure

Authors: Ling-Xiao Wang, Lei Xu, Ai-Ping Liu, Guang-Jie Chen, Yuan-Hao Yang, Jia-Qi Wang, Xin-Biao Xu, Guang-Can Guo, Chang-Ling Zou, Guo-Yong Xiang

Abstract: We propose and demonstrate a general mechanism for nanoscale lensing based on the phase gradient imposed by a single nanostructure scattering light in its near-field. We verify this effect using an optical waveguide on a substrate, with single atoms serving as quantum probes that sample the near-field intensity through their fluorescence. This quantum probing technique provides a unique, non-destr… ▽ More We propose and demonstrate a general mechanism for nanoscale lensing based on the phase gradient imposed by a single nanostructure scattering light in its near-field. We verify this effect using an optical waveguide on a substrate, with single atoms serving as quantum probes that sample the near-field intensity through their fluorescence. This quantum probing technique provides a unique, non-destructive approach to characterizing focused optical fields and reveals a 4-fold enhancement in single atom detection efficiency. This work establishes on-chip nanostructures as a multi-functional quantum optics platform that can efficiently route photons, localize fields, and enhance atom-photon coupling, offering new opportunities for trapping and manipulating single atoms and realizing hybrid nanophotonic-atomic systems for quantum applications. △ Less

Submitted 20 August, 2026; originally announced August 2026.

Comments: 12 pages, 9 figures

Beating three-parameter precision trade-offs with entangling collective measurements

Authors: Simon K. Yung, Wen-Zhe Yan, Lan-Tian Feng, Aritra Das, Jiayi Qin, Guang-Can Guo, Ping Koy Lam, Jie Zhao, Zhibo Hou, Lorcan O. Conlon, Syed M. Assad, Xi-Feng Ren, Guo-Yong Xiang

Abstract: Quantum-mechanical incompatibility, which precludes the simultaneous precise measurement of non-commuting observables, imposes fundamental limits on the rate at which classical information can be extracted. While the potential to surpass these limits using entangling collective measurements has been explored for two parameters, the regime of three or more parameters remains largely unexplored desp… ▽ More Quantum-mechanical incompatibility, which precludes the simultaneous precise measurement of non-commuting observables, imposes fundamental limits on the rate at which classical information can be extracted. While the potential to surpass these limits using entangling collective measurements has been explored for two parameters, the regime of three or more parameters remains largely unexplored despite its fundamental and technological importance. Here, we investigate the three-parameter trade-off relations for estimating the Bloch vector components of a qubit, comparing conventional individual measurements with entangling collective measurements. We theoretically derive and experimentally implement optimal collective measurements on two identically prepared qubits using a programmable photonic circuit. Our experimental results demonstrate a clear violation of the entanglement-free trade-off relation -- by an average of 16 standard deviations -- achieving a tomography precision beyond the reach of any individual measurement scheme. This work directly confirms that optimal collective measurements can surpass the fundamental quantum limits of individual schemes in a three-parameter setting -- thereby deepening our understanding of quantum uncertainty relations beyond the two-parameter regime and providing a clear strategy to overcome the precision trade-offs imposed by quantum incompatibility. △ Less

Submitted 9 April, 2026; originally announced April 2026.

A single programmable photonic circuit for universal quantum measurements

Authors: Wen-Zhe Yan, Lan-Tian Feng, Zhibo Hou, Yuan-Yuan Zhao, Carles Roch i Carceller, Armin Tavakoli, Huangjun Zhu, Guang-Can Guo, Xi-Feng Ren, Guo-Yong Xiang

Abstract: Programmable photonic quantum processors face a critical challenge: despite significant advances in quantum state preparation and manipulation, measurements remain limited to projective techniques. Here, we demonstrate a programmable measurement processor that overcomes this limitation by enabling arbitrary quantum measurements within a scalable circuit framework. Our large-scale integrated photon… ▽ More Programmable photonic quantum processors face a critical challenge: despite significant advances in quantum state preparation and manipulation, measurements remain limited to projective techniques. Here, we demonstrate a programmable measurement processor that overcomes this limitation by enabling arbitrary quantum measurements within a scalable circuit framework. Our large-scale integrated photonic architecture achieves precise coherent control of ancillary quantum systems, realizing a universal four-dimensional quantum measurement device. We benchmark the processor by performing measurement tomography on 100 randomly selected measurements, achieving an average fidelity of 97.7%. The processor's performance exceeds the theoretical limits of projective measurements in three key quantum information tasks: state discrimination (with 23 times lower error), state estimation (with 10.6% higher fidelity), and randomness generation (with 37% more randomness yield), demonstrating its high operational quality. This work establishes a fully programmable quantum measurement processor, advancing the development of universal quantum operations for photonic quantum information processing by providing the key missing component. △ Less

Submitted 20 March, 2026; originally announced March 2026.

Generalized collective quantum tomography: algorithm design, optimization, and validation

Authors: Shuixin Xiao, Yuanlong Wang, Zhibo Hou, Aritra Das, Ian R. Petersen, Farhad Farokhi, Guo-Yong Xiang, Jie Zhao, Daoyi Dong

Abstract: Quantum tomography is a fundamental technique for characterizing, benchmarking, and verifying quantum states and devices. It plays a crucial role in advancing quantum technologies and deepening our understanding of quantum mechanics. Collective quantum state tomography, which estimates an unknown state \r{ho} through joint measurements on multiple copies $ρ\otimes\cdots\otimesρ$ of the unknown sta… ▽ More Quantum tomography is a fundamental technique for characterizing, benchmarking, and verifying quantum states and devices. It plays a crucial role in advancing quantum technologies and deepening our understanding of quantum mechanics. Collective quantum state tomography, which estimates an unknown state \r{ho} through joint measurements on multiple copies $ρ\otimes\cdots\otimesρ$ of the unknown state, offers superior information extraction efficiency. Here we extend this framework to a generalized setting where the target becomes $S_1\otimes\cdots\otimes S_n$, with each $S_i$ representing identical or distinct quantum states, detectors, or processes from the same category. We formulate these tasks as optimization problems and develop three algorithms for collective quantum state, detector and process tomography, respectively, each accompanied by an analytical characterization of the computational complexity and mean squared error (MSE) scaling. Furthermore, we develop optimal solutions of these optimization problems using sum of squares (SOS) techniques with semi-algebraic constraints. The effectiveness of our proposed methods is demonstrated through numerical examples. Additionally, we experimentally demonstrate the algorithms using two-copy collective measurements, where entangled measurements directly provide information about the state purity. Compared to existing methods, our algorithms achieve lower MSEs and approach the collective MSE bound by effectively leveraging purity information. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Unified formalism and adaptive algorithms for optimal quantum state, detector and process tomography

Authors: Shuixin Xiao, Xiangyu Wang, Yuanlong Wang, Zhibo Hou, Jun Zhang, Ian R. Petersen, Wen-Zhe Yan, Hidehiro Yonezawa, Franco Nori, Guo-Yong Xiang, Daoyi Dong

Abstract: Quantum tomography is a standard technique for characterizing, benchmarking and verifying quantum systems/devices and plays a vital role in advancing quantum technology and understanding the foundations of quantum mechanics. Achieving the highest possible tomography accuracy remains a central challenge. Here we unify the infidelity metrics for quantum state, detector and process tomography in a si… ▽ More Quantum tomography is a standard technique for characterizing, benchmarking and verifying quantum systems/devices and plays a vital role in advancing quantum technology and understanding the foundations of quantum mechanics. Achieving the highest possible tomography accuracy remains a central challenge. Here we unify the infidelity metrics for quantum state, detector and process tomography in a single index $1-F(\hat S,S)$, where $S$ represents the true density matrix, POVM element, or process matrix, and $\hat S$ is its estimator. We establish a sufficient and necessary condition for any tomography protocol to attain the optimal scaling $1-F= O(1/N) $ where $N$ is the number of state copies consumed, in contrast to the $O(1/\sqrt{N})$ worst-case scaling of static methods. Guided by this result, we propose adaptive algorithms with provably optimal infidelity scalings for state, detector, and process tomography. Numerical simulations and quantum optical experiments validate the proposed methods, with our experiments reaching, for the first time, the optimal infidelity scaling in ancilla-assisted process tomography. △ Less

Submitted 7 September, 2025; originally announced September 2025.

Comments: 7+27 pages

Detection and manipulation of surface electric field noise of hexagonal boron nitride

Authors: Hao-Jie Zhou, Xiao-Wen Shen, Yu Zhou, Lei Dong, Pei-Qin Chen, Xia Chen, Guang-Wei Deng, Gang Xiang, Pei-Jie Guo, Tian-Ke Wang, Hong-Peng Wu, Jun-Feng Wang

Abstract: Hexagonal boron nitride (hBN) spin defects off er transformative potential for quantum sensing through atomic-scale proximity to target samples, yet their performance is fundamentally limited by rapid coherence loss. While magnetic noise mechanisms have been extensively studied, another critical infl uence from surface electric fi eld noise remains unexplored in hBN systems. Here,we address this c… ▽ More Hexagonal boron nitride (hBN) spin defects off er transformative potential for quantum sensing through atomic-scale proximity to target samples, yet their performance is fundamentally limited by rapid coherence loss. While magnetic noise mechanisms have been extensively studied, another critical infl uence from surface electric fi eld noise remains unexplored in hBN systems. Here,we address this challenge and systematically investigate surface electric fi eld noise in hBN using shallow boron vacancy defects. The double-quantum spin relaxation behavior in response to magnetic fi elds and defect depths is examined, revealing that the relaxation rate follows a distinctive depth-related power-law dependence of ODMR splitting frequency. The relaxation is also demonstrated to be independent of the defect concentrations. Furthermore, the temperature dependence of the relaxation rate is investigated, showing a noticeable rise as the temperature increases from 296 K to 453 K, thus highlighting the infl uence of thermal eff ects on spin relaxation. To further suppress surface electric fi eld noise, we explore the eff ectiveness of passivation materials, including glycerol and PMMA. Notably, PMMA is more effi cient in mitigating surface electric fi eld noise. These experiments enhance the understanding of surface electric fi eld noise in hBN and provide a foundation for developing noise mitigation strategies in future research. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Comments: 5

Optimal estimation of three parallel spins with genuine and restricted collective measurements

Authors: Changhao Yi, Kai Zhou, Zhibo Hou, Guo-Yong Xiang, Huangjun Zhu

Abstract: Collective measurements on identical and independent quantum systems can offer advantages in information extraction compared with individual measurements. However, little is known about the distinction between restricted collective measurements and genuine collective measurements in the multipartite setting. In this work we establish a rigorous performance gap based on a simple and old estimation… ▽ More Collective measurements on identical and independent quantum systems can offer advantages in information extraction compared with individual measurements. However, little is known about the distinction between restricted collective measurements and genuine collective measurements in the multipartite setting. In this work we establish a rigorous performance gap based on a simple and old estimation problem, the estimation of a random spin state given three parallel spins. Notably, we derive an analytical formula for the maximum estimation fidelity of biseparable measurements and clarify its fidelity gap from genuine collective measurements. Moreover, we clarify the structure of optimal biseparable measurements. It turns out that the maximum estimation fidelity can be achieved by two- and one-copy measurements assisted by one-way communication in one direction, but not the other way. Our work reveals a rich landscape of multipartite nonclassicality in quantum measurements instead of quantum states and is expected to trigger further studies. △ Less

Submitted 17 June, 2025; v1 submitted 4 December, 2024; originally announced December 2024.

Comments: 8+12 pages, 2 figures, and 1 table; see also the companion paper arXiv:2312.01651

Journal ref: Phys. Rev. A 111, 062409 (2025)

Noninvasive magnetic detection of 2D van der Waals room-temperature ferromagnet Fe3GaTe2 using divacancy spins in SiC

Authors: Xia Chen, Qin-Yue Luo, Pei-Jie Guo, Hao-Jie Zhou, Qi-Cheng Hu, Hong-Peng Wu, Xiao-Wen Shen, Ru-Yue Cui, Lei Dong, Tian-Xing Wei, Yu-Hang Xiao, De-Ren Li, Li Lei, Xi Zhang, Jun-Feng Wang, Gang Xiang

Abstract: Room-temperature (RT) two-dimensional (2D) van der Waals (vdW) ferromagnets hold immense promise for next-generation spintronic devices for information storage and processing. To achieve high-density energy-efficient spintronic devices, it is essential to understand local magnetic properties of RT 2D vdW magnets. In this work, we realize noninvasive in situ magnetic detection in vdW-layered ferrom… ▽ More Room-temperature (RT) two-dimensional (2D) van der Waals (vdW) ferromagnets hold immense promise for next-generation spintronic devices for information storage and processing. To achieve high-density energy-efficient spintronic devices, it is essential to understand local magnetic properties of RT 2D vdW magnets. In this work, we realize noninvasive in situ magnetic detection in vdW-layered ferromagnet Fe3GaTe2 using divacancy spins quantum sensor in silicon carbide (SiC) at RT. The structural features and magnetic properties of the Fe3GaTe2 are characterized utilizing Raman spectrum, magnetization and magneto-transport measurements. Further detailed analysis of temperature- and magnetic field-dependent optically detected magnetic resonances of the PL6 divacancy near the Fe3GaTe2 reveal that, the Curie temperature (Tc) of Fe3GaTe2 is ~360K, and the magnetization increases with external magnetic fields. Additionally, spin relaxometry technology is employed to probe the magnetic fluctuations of Fe3GaTe2, revealing a peak in the spin relaxation rate around Tc. These experiments give insights into the intriguing local magnetic properties of 2D vdW RT ferromagnet Fe3GaTe2 and pave the way for the application of SiC quantum sensors in noninvasive in situ magnetic detection of related 2D vdW magnets. △ Less

Submitted 4 June, 2024; originally announced June 2024.

Comments: 15 pages, 4 figures

Experimental Realization of Genuine Three-copy Collective Measurements for Optimal Information Extraction

Authors: Kai Zhou, Changhao Yi, Wen-Zhe Yan, Zhibo Hou, Huangjun Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Nonclassical phenomena tied to entangled states are the focus of foundational studies and powerful resources in many applications. By contrast, the counterparts in quantum measurements are still poorly understood. Notably, genuine multipartite nonclassicality is barely discussed, let alone its experimental realization. Here we experimentally demonstrate the power of genuine tripartite nonclassical… ▽ More Nonclassical phenomena tied to entangled states are the focus of foundational studies and powerful resources in many applications. By contrast, the counterparts in quantum measurements are still poorly understood. Notably, genuine multipartite nonclassicality is barely discussed, let alone its experimental realization. Here we experimentally demonstrate the power of genuine tripartite nonclassicality in quantum measurements based on a simple estimation problem. To this end we realize an optimal genuine three-copy collective measurement via a nine-step two-dimensional photonic quantum walk with 30 elaborately designed coin operators. Then we realize an optimal estimation protocol and achieve an unprecedented high estimation fidelity, which can beat all strategies based on restricted collective measurements by more than 11 standard deviations. These results clearly demonstrate that genuine collective measurements can extract more information than local measurements and restricted collective measurements. Our work opens the door for exploring genuine multipartite nonclassical measurements and their power in quantum information processing. △ Less

Submitted 17 June, 2025; v1 submitted 4 December, 2023; originally announced December 2023.

Journal ref: Physical Review Letters 134, 210201 (2025)

Experimental Demonstration of Inequivalent Mutually Unbiased Bases

Authors: Wen-Zhe Yan, Yunting Li, Zhibo Hou, Huangjun Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Quantum measurements based on mutually unbiased bases (MUB) play crucial roles in foundational studies and quantum information processing. It is known that there exist inequivalent MUB, but little is known about their operational distinctions, not to say experimental demonstration. In this work, by virtue of a simple estimation problem we experimentally demonstrate the operational distinctions bet… ▽ More Quantum measurements based on mutually unbiased bases (MUB) play crucial roles in foundational studies and quantum information processing. It is known that there exist inequivalent MUB, but little is known about their operational distinctions, not to say experimental demonstration. In this work, by virtue of a simple estimation problem we experimentally demonstrate the operational distinctions between inequivalent triples of MUB in dimension 4 based on high-precision photonic systems. The experimental estimation fidelities coincide well with the theoretical predictions with only 0.16$\%$ average deviation, which is 25 times less than the difference (4.1$\%$) between the maximum estimation fidelity and the minimum estimation fidelity. Our experiments clearly demonstrate that inequivalent MUB have different information extraction capabilities and different merits for quantum information processing. △ Less

Submitted 11 November, 2023; originally announced November 2023.

Minimum-consumption discrimination of quantum states via globally optimal adaptive measurements

Authors: Boxuan Tian, Wenzhe Yan, Zhibo Hou, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Reducing the average resource consumption is the central quest in discriminating non-orthogonal quantum states for a fixed admissible error rate $\varepsilon$. The globally optimal fixed local projective measurement (GOFL) for this task is found to be different from that for previous minimum-error discrimination tasks [PRL 118, 030502 (2017)]. To achieve the ultimate minimum average consumption, h… ▽ More Reducing the average resource consumption is the central quest in discriminating non-orthogonal quantum states for a fixed admissible error rate $\varepsilon$. The globally optimal fixed local projective measurement (GOFL) for this task is found to be different from that for previous minimum-error discrimination tasks [PRL 118, 030502 (2017)]. To achieve the ultimate minimum average consumption, here we develop a general globally optimal adaptive strategy (GOA) by subtly using the updated posterior probability, which works under any error rate requirement and any one-way measurement restrictions, and can be solved by a convergent iterative relation. First, under the local measurement restrictions, our GOA is solved to serve as the local bound, which saves 16.6 copies (24%) compared with the previously best GOFL. When the more powerful two-copy collective measurements are allowed, our GOA is experimentally demonstrated to beat the local bound by 3.9 copies (6.0%). By exploiting both adaptivity and collective measurements, our work marks an important step towards minimum-consumption quantum state discrimination. △ Less

Submitted 15 October, 2023; v1 submitted 30 July, 2023; originally announced July 2023.

Resource Theory of Imaginarity: New Distributed Scenarios

Authors: Kang-Da Wu, Tulja Varun Kondra, Carlo Maria Scandolo, Swapan Rana, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Alexander Streltsov

Abstract: The resource theory of imaginarity studies the operational value of imaginary parts in quantum states, operations, and measurements. Here we introduce and study the distillation and conversion of imaginarity in distributed scenario. This arises naturally in bipartite systems where both parties work together to generate the maximum possible imaginarity on one of the subsystems. We give exact soluti… ▽ More The resource theory of imaginarity studies the operational value of imaginary parts in quantum states, operations, and measurements. Here we introduce and study the distillation and conversion of imaginarity in distributed scenario. This arises naturally in bipartite systems where both parties work together to generate the maximum possible imaginarity on one of the subsystems. We give exact solutions to this problem for general qubit states and pure states of arbitrary dimension. We present a scenario that demonstrates the operational advantage of imaginarity: the discrimination of quantum channels without the aid of an ancillary system. We then link this scenario to LOCC discrimination of bipartite states. We experimentally demonstrate the relevant assisted distillation protocol, and show the usefulness of imaginarity in the aforementioned two tasks. △ Less

Submitted 11 January, 2023; originally announced January 2023.

Journal ref: Commun Phys 7, 171 (2024)

Implementing quantum dimensionality reduction for non-Markovian stochastic simulation

Authors: Kang-Da Wu, Chengran Yang, Ren-Dong He, Mile Gu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Thomas J. Elliott

Abstract: Complex systems are embedded in our everyday experience. Stochastic modelling enables us to understand and predict the behaviour of such systems, cementing its utility across the quantitative sciences. Accurate models of highly non-Markovian processes -- where the future behaviour depends on events that happened far in the past -- must track copious amounts of information about past observations,… ▽ More Complex systems are embedded in our everyday experience. Stochastic modelling enables us to understand and predict the behaviour of such systems, cementing its utility across the quantitative sciences. Accurate models of highly non-Markovian processes -- where the future behaviour depends on events that happened far in the past -- must track copious amounts of information about past observations, requiring high-dimensional memories. Quantum technologies can ameliorate this cost, allowing models of the same processes with lower memory dimension than corresponding classical models. Here we implement such memory-efficient quantum models for a family of non-Markovian processes using a photonic setup. We show that with a single qubit of memory our implemented quantum models can attain higher precision than possible with any classical model of the same memory dimension. This heralds a key step towards applying quantum technologies in complex systems modelling. △ Less

Submitted 18 October, 2023; v1 submitted 26 August, 2022; originally announced August 2022.

Comments: 11+2 pages, 5 figures

Journal ref: Nature Communications 14, 2624 (2023)

Universal device for two-qubit entangled measurements via photonic quantum walks

Authors: Wen-Zhe Yan, Zhibo Hou, Jun-Feng Tang, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Marc-Olivier Renou

Abstract: Sophisticated quantum measurements are fundamental to obtain a quantum advantage in many informational problems. Here, we consider the task of guessing a direction encoded in a two-qubit pure state. We experimentally demonstrate that abstention can be used to recover optimal direction guessing (measured in terms of the fidelity and maximum likelihood scores) even from non ideal states. Our protoco… ▽ More Sophisticated quantum measurements are fundamental to obtain a quantum advantage in many informational problems. Here, we consider the task of guessing a direction encoded in a two-qubit pure state. We experimentally demonstrate that abstention can be used to recover optimal direction guessing (measured in terms of the fidelity and maximum likelihood scores) even from non ideal states. Our protocol uses nine-step photonic quantum walks to implement the optimal five-output two-qubit collective measurements with fidelities above 0.9850. Thanks to abstention, we obtain more than a 10-fold improvement of the direction guessing scores (in terms of deviation to the optimal guessing scores). Our work demonstrates the versatility of photonic quantum walks for implementing many-qubit sophisticated measurements. △ Less

Submitted 27 February, 2024; v1 submitted 24 April, 2022; originally announced April 2022.

Comments: Comments welcome! 5 pages + 12 pages appendix

Neural networks for quantum state tomography with constrained measurements

Authors: Hailan Ma, Daoyi Dong, Ian R. Petersen, Chang-Jiang Huang, Guo-Yong Xiang

Abstract: Quantum state tomography (QST) aiming at reconstructing the density matrix of a quantum state plays an important role in various emerging quantum technologies. Recognizing the challenges posed by imperfect measurement data, we develop a unified neural network(NN)-based approach for QST under constrained measurement scenarios, including limited measurement copies, incomplete measurements, and noisy… ▽ More Quantum state tomography (QST) aiming at reconstructing the density matrix of a quantum state plays an important role in various emerging quantum technologies. Recognizing the challenges posed by imperfect measurement data, we develop a unified neural network(NN)-based approach for QST under constrained measurement scenarios, including limited measurement copies, incomplete measurements, and noisy measurements. Through comprehensive comparison with other estimation methods, we demonstrate that our method improves the estimation accuracy in scenarios with limited measurement resources, showcasing notable robustness in noisy measurement settings. These findings highlight the capability of NNs to enhance QST with constrained measurements. △ Less

Submitted 28 March, 2025; v1 submitted 17 November, 2021; originally announced November 2021.

Journal ref: Quantum Information Processing (2024) 23:317

Efficient Experimental Verification of Quantum Gates with Local Operations

Authors: Rui-Qi Zhang, Zhibo Hou, Jun-Feng Tang, Jiangwei Shang, Huangjun Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Verifying the correct functioning of quantum gates is a crucial step towards reliable quantum information processing, but it becomes an overwhelming challenge as the system size grows due to the dimensionality curse. Recent theoretical breakthroughs show that it is possible to verify various important quantum gates with the optimal sample complexity of $O(1/ε)$ using local operations only, where… ▽ More Verifying the correct functioning of quantum gates is a crucial step towards reliable quantum information processing, but it becomes an overwhelming challenge as the system size grows due to the dimensionality curse. Recent theoretical breakthroughs show that it is possible to verify various important quantum gates with the optimal sample complexity of $O(1/ε)$ using local operations only, where $ε$ is the estimation precision. In this work, we propose a variant of quantum gate verification (QGV) which is robust to practical gate imperfections, and experimentally realize efficient QGV on a two-qubit controlled-not gate and a three-qubit Toffoli gate using only local state preparations and measurements. The experimental results show that, by using only 1600 and 2600 measurements on average, we can verify with 95% confidence level that the implemented controlled-not gate and Toffoli gate have fidelities at least 99% and 97%, respectively. Demonstrating the superior low sample complexity and experimental feasibility of QGV, our work promises a solution to the dimensionality curse in verifying large quantum devices in the quantum era. △ Less

Submitted 5 July, 2021; originally announced July 2021.

Experimental Masking of Real Quantum States

Authors: Rui-Qi Zhang, Zhibo Hou, Zihao Li, Huangjun Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Masking of quantum information is a way of hiding information in correlations such that no information is accessible to any local observer. Although the set of all quantum states as a whole cannot be masked into bipartite correlations according to the no-masking theorem, the set of real states is maskable and is a maximal maskable set. In this work, we experimentally realize a masking protocol of… ▽ More Masking of quantum information is a way of hiding information in correlations such that no information is accessible to any local observer. Although the set of all quantum states as a whole cannot be masked into bipartite correlations according to the no-masking theorem, the set of real states is maskable and is a maximal maskable set. In this work, we experimentally realize a masking protocol of the real ququart by virtue of a photonic quantum walk. Our experiment clearly demonstrates that quantum information of the real ququart can be completely hidden in bipartite correlations of two-qubit hybrid entangled states, which are encoded in two different degrees of freedom of a single photon. The hidden information is not accessible from each qubit alone, but can be faithfully retrieved with a fidelity of about 99% from correlation measurements. By contrast, any superset of the set of real density matrices cannot be masked. △ Less

Submitted 5 July, 2021; v1 submitted 4 July, 2021; originally announced July 2021.

Journal ref: Phys. Rev. Applied 16, 024052 (2021)

Preserving quantum correlations and coherence with non-Markovianity

Authors: Marek Miller, Kang-Da Wu, Manfredi Scalici, Jan Kolodynski, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Alexander Streltsov

Abstract: Open quantum systems exhibit a rich phenomenology, in comparison to closed quantum systems that evolve unitarily according to the Schrödinger equation. The dynamics of an open quantum system are typically classified into Markovian and non-Markovian, depending on whether the dynamics can be decomposed into valid quantum operations at any time scale. Since Markovian evolutions are easier to simulate… ▽ More Open quantum systems exhibit a rich phenomenology, in comparison to closed quantum systems that evolve unitarily according to the Schrödinger equation. The dynamics of an open quantum system are typically classified into Markovian and non-Markovian, depending on whether the dynamics can be decomposed into valid quantum operations at any time scale. Since Markovian evolutions are easier to simulate, compared to non-Markovian dynamics, it is reasonable to assume that non-Markovianity can be employed for useful quantum-technological applications. Here, we demonstrate the usefulness of non-Markovianity for preserving correlations and coherence in quantum systems. For this, we consider a broad class of qubit evolutions, having a decoherence matrix separated from zero for large times. While any such Markovian evolution leads to an exponential loss of correlations, non-Markovianity can help to preserve correlations even in the limit $t \rightarrow \infty$. For covariant qubit evolutions, we also show that non-Markovianity can be used to preserve quantum coherence at all times, which is an important resource for quantum metrology. We explicitly demonstrate this effect experimentally with linear optics, by implementing the required evolution that is non-Markovian at all times. △ Less

Submitted 25 June, 2021; originally announced June 2021.

Journal ref: New J. Phys. 24, 053022 (2022)

Experimental study of quantum uncertainty from lack of information

Authors: Yuan-Yuan Zhao, Filip Rozpędek, Zhibo Hou, Kang-Da Wu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Quantum uncertainty is a well-known property of quantum mechanics that states the impossibility of predicting measurement outcomes of multiple incompatible observables simultaneously. In contrast, the uncertainty in the classical domain comes from the lack of information about the exact state of the system. One may naturally ask, whether the quantum uncertainty is indeed a fully intrinsic property… ▽ More Quantum uncertainty is a well-known property of quantum mechanics that states the impossibility of predicting measurement outcomes of multiple incompatible observables simultaneously. In contrast, the uncertainty in the classical domain comes from the lack of information about the exact state of the system. One may naturally ask, whether the quantum uncertainty is indeed a fully intrinsic property of the quantum theory, or whether similarly to the classical domain lack of knowledge about specific parts of the physical system might be the source of this uncertainty. This question has been addressed in the previous literature where the authors argue that in the entropic formulation of the uncertainty principle that can be illustrated using the, so-called, guessing games, indeed such lack of information has a significant contribution to the arising quantum uncertainty. Here we investigate this issue experimentally by implementing the corresponding two-dimensional and three-dimensional guessing games. Our results confirm that within the guessing-game framework, the quantum uncertainty to a large extent relies on the fact that quantum information determining the key properties of the game is stored in the degrees of freedom that remain inaccessible to the guessing party. Moreover, we offer an experimentally compact method to construct the high-dimensional Fourier gate which is a major building block for various tasks in quantum computation, quantum communication, and quantum metrology. △ Less

Submitted 4 May, 2023; v1 submitted 19 May, 2021; originally announced May 2021.

Comments: close to the version published in npj quantum information

Journal ref: npj Quantum Inf 8, 64 (2022)

Experimental progress on quantum coherence: detection, quantification, and manipulation

Authors: Kang-Da Wu, Alexander Streltsov, Bartosz Regula, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Quantum coherence is a fundamental property of quantum systems, separating quantum from classical physics. Recently, there has been significant interest in the characterization of quantum coherence as a resource, investigating how coherence can be extracted and used for quantum technological applications. In this work we review the progress of this research, focusing in particular on recent experi… ▽ More Quantum coherence is a fundamental property of quantum systems, separating quantum from classical physics. Recently, there has been significant interest in the characterization of quantum coherence as a resource, investigating how coherence can be extracted and used for quantum technological applications. In this work we review the progress of this research, focusing in particular on recent experimental efforts. After a brief review of the underlying theory we discuss the main platforms for realizing the experiments: linear optics, nuclear magnetic resonance, and superconducting systems. We then consider experimental detection and quantification of coherence, experimental state conversion and coherence distillation, and experiments investigating the dynamics of quantum coherence. We also review experiments exploring the connections between coherence and uncertainty relations, path information, and coherence of operations and measurements. Experimental efforts on multipartite and multilevel coherence are also discussed. △ Less

Submitted 15 July, 2021; v1 submitted 14 May, 2021; originally announced May 2021.

Journal ref: Adv. Quantum Technol. 2100040 (2021)

Resource theory of imaginarity: Quantification and state conversion

Authors: Kang-Da Wu, Tulja Varun Kondra, Swapan Rana, Carlo Maria Scandolo, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Alexander Streltsov

Abstract: Complex numbers are widely used in both classical and quantum physics, and are indispensable components for describing quantum systems and their dynamical behavior. Recently, the resource theory of imaginarity has been introduced, allowing for a systematic study of complex numbers in quantum mechanics and quantum information theory. In this work we develop theoretical methods for the resource theo… ▽ More Complex numbers are widely used in both classical and quantum physics, and are indispensable components for describing quantum systems and their dynamical behavior. Recently, the resource theory of imaginarity has been introduced, allowing for a systematic study of complex numbers in quantum mechanics and quantum information theory. In this work we develop theoretical methods for the resource theory of imaginarity, motivated by recent progress within theories of entanglement and coherence. We investigate imaginarity quantification, focusing on the geometric imaginarity and the robustness of imaginarity, and apply these tools to the state conversion problem in imaginarity theory. Moreover, we analyze the complexity of real and general operations in optical experiments, focusing on the number of unfixed wave plates for their implementation. We also discuss the role of imaginarity for local state discrimination, proving that any pair of real orthogonal pure states can be discriminated via local real operations and classical communication. Our study reveals the significance of complex numbers in quantum physics, and proves that imaginarity is a resource in optical experiments. △ Less

Submitted 2 March, 2021; originally announced March 2021.

Comments: 13 pages, 2 figures. Accompanying article for arXiv:2007.14847

Journal ref: Phys. Rev. A 103, 032401 (2021)

Minimizing back-action through entangled measurements

Authors: Kang-Da Wu, Elisa Bäumer, Jun-Feng Tang, Karen V. Hovhannisyan, Martí Perarnau-Llobet, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: When an observable is measured on an evolving coherent quantum system twice, the first measurement generally alters the statistics of the second one, which is known as measurement back-action. We introduce, and push to its theoretical and experimental limits, a novel method of back-action evasion, whereby entangled collective measurements are performed on several copies of the system. This method… ▽ More When an observable is measured on an evolving coherent quantum system twice, the first measurement generally alters the statistics of the second one, which is known as measurement back-action. We introduce, and push to its theoretical and experimental limits, a novel method of back-action evasion, whereby entangled collective measurements are performed on several copies of the system. This method is inspired by a similar idea designed for the problem of measuring quantum work [Perarnau-Llobet \textit{et al}., (https://doi.org/10.1103/PhysRevLett.118.070601) Phys. Rev. Lett. \textbf{118}, 070601 (2017)]. By utilizing entanglement as a resource, we show that the back-action can be extremely suppressed compared to all previous schemes. Importantly, the back-action can be eliminated in highly coherent processes. △ Less

Submitted 18 November, 2020; originally announced November 2020.

Journal ref: Phys. Rev. Lett. 125, 210401 (2020)

Nonlocality, steering and quantum state tomography in a single experiment

Authors: Chang-Jiang Huang, Guo-Yong Xiang, Yu Guo, Kang-Da Wu, Bi-Heng Liu, Chuan-Feng Li, Guang-Can Guo, Armin Tavakoli

Abstract: We investigate whether paradigmatic measurements for quantum state tomography, namely mutually unbiased bases and symmetric informationally complete measurements, can be employed to certify quantum correlations. For this purpose, we identify a simple and noise-robust correlation witness for entanglement detection, steering and nonlocality that can be evaluated based on the outcome statistics obtai… ▽ More We investigate whether paradigmatic measurements for quantum state tomography, namely mutually unbiased bases and symmetric informationally complete measurements, can be employed to certify quantum correlations. For this purpose, we identify a simple and noise-robust correlation witness for entanglement detection, steering and nonlocality that can be evaluated based on the outcome statistics obtained in the tomography experiment. This allows us to perform state tomography on entangled qutrits, a test of Einstein-Podolsky-Rosen steering and a Bell inequality test, all within a single experiment. We also investigate the trade-off between quantum correlations and subsets of tomographically complete measurements as well as the quantification of entanglement in the different scenarios. Finally, we perform a photonics experiment in which we demonstrate quantum correlations under these flexible assumptions, namely with both parties trusted, one party untrusted and both parties untrusted. △ Less

Submitted 14 August, 2021; v1 submitted 11 November, 2020; originally announced November 2020.

Comments: See also the communication game of arXiv:2007.15643 to which our nonlocal game is strongly related

Journal ref: Phys. Rev. Lett. 127, 020401 (2021)

Operational Resource Theory of Imaginarity

Authors: Kang-Da Wu, Tulja Varun Kondra, Swapan Rana, Carlo Maria Scandolo, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Alexander Streltsov

Abstract: Wave-particle duality is one of the basic features of quantum mechanics, giving rise to the use of complex numbers in describing states of quantum systems, their dynamics, and interaction. Since the inception of quantum theory, it has been debated whether complex numbers are actually essential, or whether an alternative consistent formulation is possible using real numbers only. Here, we attack th… ▽ More Wave-particle duality is one of the basic features of quantum mechanics, giving rise to the use of complex numbers in describing states of quantum systems, their dynamics, and interaction. Since the inception of quantum theory, it has been debated whether complex numbers are actually essential, or whether an alternative consistent formulation is possible using real numbers only. Here, we attack this long-standing problem both theoretically and experimentally, using the powerful tools of quantum resource theories. We show that - under reasonable assumptions - quantum states are easier to create and manipulate if they only have real elements. This gives an operational meaning to the resource theory of imaginarity. We identify and answer several important questions which include the state-conversion problem for all qubit states and all pure states of any dimension, and the approximate imaginarity distillation for all quantum states. As an application, we show that imaginarity plays a crucial role for state discrimination: there exist real quantum states which can be perfectly distinguished via local operations and classical communication, but which cannot be distinguished with any nonzero probability if one of the parties has no access to imaginarity. We confirm this phenomenon experimentally with linear optics, performing discrimination of different two-photon quantum states by local projective measurements. These results prove that complex numbers are an indispensable part of quantum mechanics. △ Less

Submitted 2 March, 2021; v1 submitted 29 July, 2020; originally announced July 2020.

Comments: 6+2 pages, 2 figures

Journal ref: Phys. Rev. Lett. 126, 090401 (2021)

On compression rate of quantum autoencoders: Control design, numerical and experimental realization

Authors: Hailan Ma, Chang-Jiang Huang, Chunlin Chen, Daoyi Dong, Yuanlong Wang, Re-Bing Wu, Guo-Yong Xiang

Abstract: Quantum autoencoders which aim at compressing quantum information in a low-dimensional latent space lie in the heart of automatic data compression in the field of quantum information. In this paper, we establish an upper bound of the compression rate for a given quantum autoencoder and present a learning control approach for training the autoencoder to achieve the maximal compression rate. The upp… ▽ More Quantum autoencoders which aim at compressing quantum information in a low-dimensional latent space lie in the heart of automatic data compression in the field of quantum information. In this paper, we establish an upper bound of the compression rate for a given quantum autoencoder and present a learning control approach for training the autoencoder to achieve the maximal compression rate. The upper bound of the compression rate is theoretically proven using eigen-decomposition and matrix differentiation, which is determined by the eigenvalues of the density matrix representation of the input states. Numerical results on 2-qubit and 3-qubit systems are presented to demonstrate how to train the quantum autoencoder to achieve the theoretically maximal compression, and the training performance using different machine learning algorithms is compared. Experimental results of a quantum autoencoder using quantum optical systems are illustrated for compressing two 2-qubit states into two 1-qubit states. △ Less

Submitted 27 June, 2022; v1 submitted 22 May, 2020; originally announced May 2020.

Generation of accessible sets in the dynamical modelling of quantum network systems

Authors: Qi Yu, Yuanlong Wang, Daoyi Dong, Ian R. Petersen, Guo-Yong Xiang

Abstract: In this paper, we consider the dynamical modeling of a class of quantum network systems consisting of qubits. Qubit probes are employed to measure a set of selected nodes of the quantum network systems. For a variety of applications, a state space model is a useful way to model the system dynamics. To construct a state space model for a quantum network system, the major task is to find an accessib… ▽ More In this paper, we consider the dynamical modeling of a class of quantum network systems consisting of qubits. Qubit probes are employed to measure a set of selected nodes of the quantum network systems. For a variety of applications, a state space model is a useful way to model the system dynamics. To construct a state space model for a quantum network system, the major task is to find an accessible set containing all of the operators coupled to the measurement operators. This paper focuses on the generation of a proper accessible set for a given system and measurement scheme. We provide analytic results on simplifying the process of generating accessible sets for systems with a time-independent Hamiltonian. Since the order of elements in the accessible set determines the form of state space matrices, guidance is provided to effectively arrange the ordering of elements in the state vector. Defining a system state according to the accessible set, one can develop a state space model with a special pattern inherited from the system structure. As a demonstration, we specifically consider a typical 1D-chain system with several common measurements, and employ the proposed method to determine its accessible set. △ Less

Submitted 30 April, 2020; originally announced April 2020.

Experimental optimal orienteering via parallel and antiparallel spins

Authors: Jun-Feng Tang, Zhibo Hou, Jiangwei Shang, Huangjun Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Antiparallel spins are superior in orienteering to parallel spins. This intriguing phenomenon is tied to entanglement associated with quantum measurements rather than quantum states. Using photonic systems, we experimentally realize the optimal orienteering protocols based on parallel spins and antiparallel spins, respectively. The optimal entangling measurements for decoding the direction informa… ▽ More Antiparallel spins are superior in orienteering to parallel spins. This intriguing phenomenon is tied to entanglement associated with quantum measurements rather than quantum states. Using photonic systems, we experimentally realize the optimal orienteering protocols based on parallel spins and antiparallel spins, respectively. The optimal entangling measurements for decoding the direction information from parallel spins and antiparallel spins are realized using photonic quantum walks, which is a useful idea that is of wide interest in quantum information processing and foundational studies. Our experiments clearly demonstrate the advantage of antiparallel spins over parallel spins in orienteering. In addition, entangling measurements can extract more information than local measurements even if no entanglement is present in the quantum states. △ Less

Submitted 17 February, 2020; originally announced February 2020.

Journal ref: Physical Review Letters 124, 060502(2020)

Testing a Quantum Error-Correcting Code on Various Platforms

Authors: Qihao Guo, Yuan-Yuan Zhao, Markus Grassl, Xinfang Nie, Guo-Yong Xiang, Tao Xin, Zhang-Qi Yin, Bei Zeng

Abstract: Quantum error correction plays an important role in fault-tolerant quantum information processing. It is usually difficult to experimentally realize quantum error correction, as it requires multiple qubits and quantum gates with high fidelity. Here we propose a simple quantum error-correcting code for the detected amplitude damping channel. The code requires only two qubits. We implement the encod… ▽ More Quantum error correction plays an important role in fault-tolerant quantum information processing. It is usually difficult to experimentally realize quantum error correction, as it requires multiple qubits and quantum gates with high fidelity. Here we propose a simple quantum error-correcting code for the detected amplitude damping channel. The code requires only two qubits. We implement the encoding, the channel, and the recovery on an optical platform, the IBM Q System, and a nuclear magnetic resonance system. For all of these systems, the error correction advantage appears when the damping rate exceeds some threshold. We compare the features of these quantum information processing systems used and demonstrate the advantage of quantum error correction on current quantum computing platforms. △ Less

Submitted 22 January, 2020; originally announced January 2020.

Comments: 26 pages, 9 figures, 4 tables

Journal ref: Science Bulletin, 2020

Ultimate precision of multi-parameter quantum magnetometry under the parallel scheme

Authors: Zhibo Hou, Hongzhen Chen, Liqiang Liu, Zhao Zhang, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Haidong Yuan

Abstract: The precise measurement of a magnetic field is one of the most fundamental and important tasks in quantum metrology. Although extensive studies on quantum magnetometry have been carried out over past decades, the ultimate precision that can be achieved for the estimation of all three components of a magnetic field with entangled probe states under the parallel scheme remains unknown. Here we prese… ▽ More The precise measurement of a magnetic field is one of the most fundamental and important tasks in quantum metrology. Although extensive studies on quantum magnetometry have been carried out over past decades, the ultimate precision that can be achieved for the estimation of all three components of a magnetic field with entangled probe states under the parallel scheme remains unknown. Here we present the ultimate lower bound for the sum of arbitrarily weighted variances in the estimation of all three components of a magnetic field under the parallel scheme and show that this lower bound can be achieved for sufficiently large N. The optimal entangled probe state that achieves the ultimate precision is also explicitly constructed. The obtained precision sets the ultimate limit for the multi-parameter quantum magnetometry under the parallel scheme, which is of fundamental interest and importance in quantum metrology. Our approach also provides a way to characterize the tradeoff among the precisions of multiple parameters that arise from the constraints on the probe states. △ Less

Submitted 8 January, 2020; originally announced January 2020.

Comments: 20 pages. Comments are welcome

Journal ref: Phys. Rev. Lett. 125, 020501 (2020)

Direct estimation of quantum coherence by collective measurements

Authors: Yuan Yuan, Zhibo Hou, Jun-Feng Tang, Alexander Streltsov, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: The recently established resource theory of quantum coherence allows for a quantitative understanding of the superposition principle, with applications reaching from quantum computing to quantum biology. While different quantifiers of coherence have been proposed in the literature, their efficient estimation in today's experiments remains a challenge. Here, we introduce a collective measurement sc… ▽ More The recently established resource theory of quantum coherence allows for a quantitative understanding of the superposition principle, with applications reaching from quantum computing to quantum biology. While different quantifiers of coherence have been proposed in the literature, their efficient estimation in today's experiments remains a challenge. Here, we introduce a collective measurement scheme for estimating the amount of coherence in quantum states, which requires entangled measurements on two copies of the state. As we show by numerical simulations, our scheme outperforms other estimation methods based on tomography or adaptive measurements, leading to a higher precision in a large parameter range for estimating established coherence quantifiers of qubit and qutrit states. We show that our method is accessible with today's technology by implementing it experimentally with photons, finding a good agreement between experiment and theory. △ Less

Submitted 5 January, 2020; originally announced January 2020.

Comments: 8 pages, 5 figures

Strong Majorization Uncertainty Relations: Theory and Experiment

Authors: Yuan Yuan, Yunlong Xiao, Zhibo Hou, Shao-Ming Fei, Gilad Gour, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: In spite of enormous theoretical and experimental progresses in quantum uncertainty relations, the experimental investigation of most current, and universal formalism of uncertainty relations, namely majorization uncertainty relations (MURs), has not been implemented yet. A significant problem is that previous studies on the classification of MURs only focus on their mathematical expressions, whil… ▽ More In spite of enormous theoretical and experimental progresses in quantum uncertainty relations, the experimental investigation of most current, and universal formalism of uncertainty relations, namely majorization uncertainty relations (MURs), has not been implemented yet. A significant problem is that previous studies on the classification of MURs only focus on their mathematical expressions, while the physical difference between various forms remains unknown. First, we use a guessing game formalism to study the MURs, which helps us disclosing their physical nature, and distinguishing the essential differences of physical features between diverse forms of MURs. Second, we tighter the bounds of MURs in terms of flatness processes, or equivalently, in terms of majorization lattice. Third, to benchmark our theoretical results, we experimentally verify MURs in the photonic systems. △ Less

Submitted 31 December, 2019; originally announced December 2019.

Comments: 13 pages, 4 figures

Device-independent verification of Einstein-Podolsky-Rosen steering

Authors: Yuan-Yuan Zhao, Chao Zhang, Shuming Cheng, Xinhui Li, Yu Guo, Bi-Heng Liu, Huan-Yu Ku, Shin-Liang Chen, Qiaoyan Wen, Yun-Feng Huang, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Entanglement lies at the heart of quantum mechanics, and has been identified an essential resource for diverse applications in quantum information. If entanglement could be verified without any trust in the devices of observers, i.e., in a device-independent (DI) way, then unconditional security can be guaranteed for various quantum information tasks. In this work, we propose an experimental-frien… ▽ More Entanglement lies at the heart of quantum mechanics, and has been identified an essential resource for diverse applications in quantum information. If entanglement could be verified without any trust in the devices of observers, i.e., in a device-independent (DI) way, then unconditional security can be guaranteed for various quantum information tasks. In this work, we propose an experimental-friendly DI protocol to certify the presence of entanglement, based on Einstein-Podolsky-Rosen (EPR) steering. We first establish the DI verification framework, relying on the measurement-device-independent technique and self-testing, and show it is able to verify all EPR-steerable states. In the context of three-measurement settings as per party, it is found to be noise robustness towards inefficient measurements and imperfect self-testing. Finally, a four-photon experiment is implemented to device-independently verify EPR-steering even for Bell local states. Our work paves the way for realistic implementations of secure quantum information tasks. △ Less

Submitted 5 February, 2023; v1 submitted 29 September, 2019; originally announced September 2019.

Comments: Experiments are rerun to collect more data to do tomography and the text is significantly refined; Comments are still welcome

Journal ref: Optica 10, 1 (2023)

Experimental realization of self-guided quantum process tomography

Authors: Zhibo Hou, Jun-Feng Tang, Christopher Ferrie, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Characterization of quantum processes is a preliminary step necessary in the development of quantum technology. The conventional method uses standard quantum process tomography, which requires $d^2$ input states and $d^4$ quantum measurements for a $d$-dimensional Hilbert space. These experimental requirements are compounded by the complexity of processing the collected data, which can take severa… ▽ More Characterization of quantum processes is a preliminary step necessary in the development of quantum technology. The conventional method uses standard quantum process tomography, which requires $d^2$ input states and $d^4$ quantum measurements for a $d$-dimensional Hilbert space. These experimental requirements are compounded by the complexity of processing the collected data, which can take several orders of magnitude longer than the experiment itself. In this paper we propose an alternative self-guided algorithm for quantum process tomography, tuned for the task of finding an unknown unitary process. Our algorithm is a fully automated and adaptive process characterization technique. The advantages of our algorithm are: inherent robustness to both statistical and technical noise; requires less space and time since there is no post-processing of the data; requires only a single input state and measurement; and, provides on-the-fly diagnostic information while the experiment is running. Numerical results show our algorithm achieves the same $1/n$ scaling as standard quantum process tomography when $n$ uses of the unknown process are used. We also present experimental results wherein the algorithm, and its advantages, are realized for the task of finding an element of $SU(2)$. △ Less

Submitted 2 August, 2019; originally announced August 2019.

Journal ref: Phys. Rev. A 101, 022317 (2020)

Realization of a quantum autoencoder for lossless compression of quantum data

Authors: Chang-Jiang Huang, Hailan Ma, Qi Yin, Jun-Feng Tang, Daoyi Dong, Chunlin Chen, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: As a ubiquitous aspect of modern information technology, data compression has a wide range of applications. Therefore, a quantum autoencoder which can compress quantum information into a low-dimensional space is fundamentally important to achieve automatic data compression in the field of quantum information. Such a quantum autoencoder can be implemented through training the parameters of a quantu… ▽ More As a ubiquitous aspect of modern information technology, data compression has a wide range of applications. Therefore, a quantum autoencoder which can compress quantum information into a low-dimensional space is fundamentally important to achieve automatic data compression in the field of quantum information. Such a quantum autoencoder can be implemented through training the parameters of a quantum device using classical optimization algorithms. In this article, we analyze the condition of achieving a perfect quantum autoencoder and theoretically prove that a quantum autoencoder can losslessly compress high-dimensional quantum information into a low-dimensional space (also called latent space) if the number of maximum linearly independent vectors from input states is no more than the dimension of the latent space. Also, we experimentally realize a universal two-qubit unitary gate and design a quantum autoencoder device by applying machine learning method. Experimental results demonstrate that our quantum autoencoder is able to compress two two-qubit states into two one-qubit states. Besides compressing quantum information, the quantum autoencoder is used to experimentally discriminate two groups of nonorthogonal states. △ Less

Submitted 6 April, 2020; v1 submitted 20 March, 2019; originally announced March 2019.

Journal ref: Phys. Rev. A 102, 032412 (2020)

Detecting Non-Markovianity via Quantified Coherence: Theory and Experiments

Authors: Kang-Da Wu, Zhibo Hou, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Daoyi Dong, Franco Nori

Abstract: The dynamics of open quantum systems and manipulation of quantum resources are both of fundamental interest in quantum physics. Here, we investigate the relation between quantum Markovianity and coherence, providing an effective way for detecting non-Markovianity based on the \textit{quantum-incoherent relative entropy of coherence} ($\mathcal{QI}$ REC). We theoretically show the relation between… ▽ More The dynamics of open quantum systems and manipulation of quantum resources are both of fundamental interest in quantum physics. Here, we investigate the relation between quantum Markovianity and coherence, providing an effective way for detecting non-Markovianity based on the \textit{quantum-incoherent relative entropy of coherence} ($\mathcal{QI}$ REC). We theoretically show the relation between completely positive (CP) divisibility and the monotonic behavior of the $\mathcal{QI}$ REC. Also we implement an all-optical experiment to demonstrate that the behavior of the $\mathcal{QI}$ REC is coincident with the entanglement shared between the system and the ancilla for both Markovian and non-Markovian evolution; while other coherence-based non-Markovian information carriers violate monotonicity, even in Markovian processes. Moreover, we experimentally observe that non-Markovianity enhances the ability of creating coherence on an ancilla. This is the first experimental study of the relation between dynamical behavior of the $\mathcal{QI}$ REC and the phenomenon of information backflow. Moreover, our method for detecting non-Markovianity is applicable to general quantum evolutions. △ Less

Submitted 8 March, 2019; originally announced March 2019.

Comments: 6+14 pages, 9 figures

Journal ref: npj Quantum Information volume 6, Article number: 55 (2020)

Experimentally reducing the quantum measurement back-action in work distributions by a collective measurement

Authors: Kang-Da Wu, Yuan Yuan, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Martí Perarnau-Llobet

Abstract: In quantum thermodynamics, the standard approach to estimate work fluctuations in unitary processes is based on two projective measurements, one performed at the beginning of the process and one at the end. The first measurement destroys any initial coherence in the energy basis, thus preventing later interference effects. In order to decrease this back-action, a scheme based on collective measure… ▽ More In quantum thermodynamics, the standard approach to estimate work fluctuations in unitary processes is based on two projective measurements, one performed at the beginning of the process and one at the end. The first measurement destroys any initial coherence in the energy basis, thus preventing later interference effects. In order to decrease this back-action, a scheme based on collective measurements has been proposed in~[PRL 118, 070601 (2017)]. Here, we report its experimental implementation in an optical system. The experiment consists of a deterministic collective measurement on identically prepared two qubits, encoded in the polarisation and path degree of a single photon. The standard two projective measurement approach is also experimentally realized for comparison. Our results show the potential of collective schemes to decrease the back-action of projective measurements, and capture subtle effects arising from quantum coherence. △ Less

Submitted 5 March, 2019; originally announced March 2019.

Comments: 9 pages, 4 figures

Journal ref: Sci. Adv. 5, eaav4944 (2019)

Quantum coherence and state conversion: theory and experiment

Authors: Kang-Da Wu, Thomas Theurer, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Martin B. Plenio, Alexander Streltsov

Abstract: The resource theory of coherence studies the operational value of superpositions in quantum technologies. A key question in this theory concerns the efficiency of manipulation and inter-conversion of the resource. Here we solve this question completely for qubit states by determining the optimal probabilities for mixed state conversions via stochastic incoherent operations. Extending the discussio… ▽ More The resource theory of coherence studies the operational value of superpositions in quantum technologies. A key question in this theory concerns the efficiency of manipulation and inter-conversion of the resource. Here we solve this question completely for qubit states by determining the optimal probabilities for mixed state conversions via stochastic incoherent operations. Extending the discussion to distributed scenarios, we introduce and address the task of assisted incoherent state conversion where the process is enhanced by making use of correlations with a second party. Building on these results, we demonstrate experimentally that the optimal state conversion probabilities can be achieved in a linear optics set-up. This paves the way towards real world applications of coherence transformations in current quantum technologies. △ Less

Submitted 4 March, 2019; originally announced March 2019.

Comments: 7+14 pages, 4+2 figures, article supersedes arXiv:1804.09467

Journal ref: npj Quantum Information 6, 22 (2020)

Control-enhanced sequential scheme for general quantum parameter estimation at the Heisenberg limit

Authors: Zhibo Hou, Rui-Jia Wang, Jun-Feng Tang, Haidong Yuan, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: The advantage of quantum metrology has been experimentally demonstrated for phase estimations where the dynamics are commuting. General noncommuting dynamics, however, can have distinct features. For example, the direct sequential scheme, which can achieve the Heisenberg scaling for the phase estimation under commuting dynamics, can have even worse performances than the classical scheme under nonc… ▽ More The advantage of quantum metrology has been experimentally demonstrated for phase estimations where the dynamics are commuting. General noncommuting dynamics, however, can have distinct features. For example, the direct sequential scheme, which can achieve the Heisenberg scaling for the phase estimation under commuting dynamics, can have even worse performances than the classical scheme under noncommuting dynamics. Here we realize a scalable optimally controlled sequential scheme, which can achieve the Heisenberg precision under general noncommuting dynamics. We also present an intuitive geometrical framework for the controlled scheme and identify sweet spots in time at which the optimal controls used in the scheme can be pre-fixed without adaptation, which simplifies the experimental protocols significantly. We successfully implement the scheme up to eight controls in an optical platform, demonstrate a precision near the Heisenberg limit. Our work opens the avenue for harvesting the power of quantum control in quantum metrology, and provides a control-enhanced recipe to achieve the Heisenberg precision under general noncommuting dynamics. △ Less

Submitted 4 February, 2019; originally announced February 2019.

Journal ref: Phys. Rev. Lett. 123, 040501 (2019)

Experimental demonstration of measurement-device-independent measure of quantum steering

Authors: Yuan-Yuan Zhao, Huan-Yu Ku, Shin-Liang Chen, Hong-Bin Chen, Franco Nori, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Yueh-Nan Chen

Abstract: Within the framework of quantum refereed steering games, quantum steerability can be certified without any assumption on the underlying state nor the measurements involved. Such a scheme is termed the measurement-device-independent (MDI) scenario. Here we introduce a measure of steerability in an MDI scenario, i.e., the result merely depends on the observed statistics and the quantum inputs. We pr… ▽ More Within the framework of quantum refereed steering games, quantum steerability can be certified without any assumption on the underlying state nor the measurements involved. Such a scheme is termed the measurement-device-independent (MDI) scenario. Here we introduce a measure of steerability in an MDI scenario, i.e., the result merely depends on the observed statistics and the quantum inputs. We prove that such a measure satisfies the convex steering monotone. Moreover, it is robust against not only measurement biases but also losses. We also experimentally estimate the amount of the measure with an entangled photon source. As two by-products, our experimental results provide lower bounds on an entanglement measure of the underlying state and an incompatible measure of the involved measurement. Our research paves a way for exploring one-side device-independent quantum information processing within an MDI framework. △ Less

Submitted 10 September, 2020; v1 submitted 24 January, 2019; originally announced January 2019.

Comments: v2:10 pages, 3 figures, published version. This version combines the previous version with the theoretical work [arXiv:1807.08901]. v1:11 pages, 3 figures. Comments welcome!

Journal ref: npj Quantum Inf 6, 77 (2020)

Experimental investigation of majorization uncertainty relations in the high-dimensional systems

Authors: Yuan Yuan, Yunlong Xiao, Zhibo Hou, Shao-Ming Fei, Gilad Gour, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Uncertainty relation is not only of fundamental importance to quantum mechanics, but also crucial to the quantum information technology. Recently, majorization formulation of uncertainty relations (MURs) have been widely studied, ranging from two measurements to multiple measurements. Here, for the first time, we experimentally investigate MURs for two measurements and multiple measurements in the… ▽ More Uncertainty relation is not only of fundamental importance to quantum mechanics, but also crucial to the quantum information technology. Recently, majorization formulation of uncertainty relations (MURs) have been widely studied, ranging from two measurements to multiple measurements. Here, for the first time, we experimentally investigate MURs for two measurements and multiple measurements in the high-dimensional systems, and study the intrinsic distinction between direct-product MURs and direct-sum MURs. The experimental results reveal that by taking different nonnegative Schur-concave functions as uncertainty measure, the two types of MURs have their own particular advantages, and also verify that there exists certain case where three-measurement majorization uncertainty relation is much stronger than the one obtained by summing pairwise two-measurement uncertainty relations. Our work not only fills the gap of experimental studies of majorization uncertainty relations, but also represents an advance in quantitatively understanding and experimental verification of majorization uncertainty relations which are universal and capture the essence of uncertainty in quantum theory. △ Less

Submitted 3 January, 2019; originally announced January 2019.

Comments: 8 pages, 5 figures

Direct Measurement of the Two-dimensional Spatial Quantum Wavefunction via Strong Measurements

Authors: Chen-Rui Zhang, Meng-Jun Hu, Zhi-Bo Hou, Jun-Feng Tang, Jie Zhu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Yong-Sheng Zhang

Abstract: Wavefunction is the foundation of quantum theory, which is assumed to give a complete description of a quantum system. For a long time, wavefunction is introduced as an abstract element of the theory and there lacks effective ways to measure it directly. The situation, however, is somewhat changed when Lundeen et al. reported the direct measurement of the quantum wavefunction via weak measurements… ▽ More Wavefunction is the foundation of quantum theory, which is assumed to give a complete description of a quantum system. For a long time, wavefunction is introduced as an abstract element of the theory and there lacks effective ways to measure it directly. The situation, however, is somewhat changed when Lundeen et al. reported the direct measurement of the quantum wavefunction via weak measurements, which gives the wavefunction a clearly operational definition [Nature 474, 188 (2011)]. The weak measurement method requires sequential measurements of conjugate observables position and momentum with the position measurement is weak enough. Surprisingly, the recent research by Vallone and Dequal shows that performing sequential strong measurements realizes the same target, in which case no approximation has to be made compared to the case of weak measurements[Phys. Rev. Lett. 116, 040502 (2016)]. Here we experimentally report the direct measurement of the two-dimensional transverse wavefunction of photons via strong measurements for the first time, which implies that an accurate and clear operational definition can be given to wavefunction. We have measured the Gaussian and Laguerre-Gaussian of l = 1 spatial wavefunctions of photons with R-square are 0.97 and 0.93 respectively. As a potentially important application, we show that the direct measurement of two-dimensional wavefunction provides an alternative way to realize digital holography of three-dimensional objects. The results presented here will not only deepen our understanding of abstract wavefunction but also have significant applications in quantum information processing and quantum imaging. △ Less

Submitted 5 November, 2018; originally announced November 2018.

Comments: 5 pages

Journal ref: Phys. Rev. A 101, 012119 (2020)

Entanglement detection by violations of noisy uncertainty relations: A proof of principle

Authors: Yuan-Yuan Zhao, Guo-Yong Xiang, Xiao-Min Hu, Bi-Heng Liu, Chuan-Feng Li, Guang-Can Guo, René Schwonnek, Ramona Wolf

Abstract: It is well-known that the violation of a local uncertainty relation can be used as an indicator for the presence of entanglement. Unfortunately, the practical use of these non-linear witnesses has been limited to few special cases in the past. However, new methods for computing uncertainty bounds became available. Here we report on an experimental implementation of uncertainty-based entanglement w… ▽ More It is well-known that the violation of a local uncertainty relation can be used as an indicator for the presence of entanglement. Unfortunately, the practical use of these non-linear witnesses has been limited to few special cases in the past. However, new methods for computing uncertainty bounds became available. Here we report on an experimental implementation of uncertainty-based entanglement witnesses, benchmarked in a regime dominated by strong local noise. We combine the new computational method with a local noise tomography in order to design noise-adapted entanglement witnesses. This proof-of-principle experiment shows that quantum noise can be successfully handled by a fully quantum model in order to enhance entanglement detection efficiencies. △ Less

Submitted 22 November, 2018; v1 submitted 12 October, 2018; originally announced October 2018.

Comments: 5+1 pages, 5+2 figures

Journal ref: Phys. Rev. Lett. 122, 220401 (2019)

Experimentally detecting a quantum change point via Bayesian inference

Authors: Shang Yu, Chang-Jiang Huang, Jian-Shun Tang, Zhih-Ahn Jia, Yi-Tao Wang, Zhi-Jin Ke, Wei Liu, Xiao Liu, Zong-Quan Zhou, Ze-Di Cheng, Jin-Shi Xu, Yu-Chun Wu, Yuan-Yuan Zhao, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Gael Sentís, Ramon Muñoz-Tapia

Abstract: Detecting a change point is a crucial task in statistics that has been recently extended to the quantum realm. A source state generator that emits a series of single photons in a default state suffers an alteration at some point and starts to emit photons in a mutated state. The problem consists in identifying the point where the change took place. In this work, we consider a learning agent that a… ▽ More Detecting a change point is a crucial task in statistics that has been recently extended to the quantum realm. A source state generator that emits a series of single photons in a default state suffers an alteration at some point and starts to emit photons in a mutated state. The problem consists in identifying the point where the change took place. In this work, we consider a learning agent that applies Bayesian inference on experimental data to solve this problem. This learning machine adjusts the measurement over each photon according to the past experimental results finds the change position in an online fashion. Our results show that the local-detection success probability can be largely improved by using such a machine learning technique. This protocol provides a tool for improvement in many applications where a sequence of identical quantum states is required. △ Less

Submitted 23 January, 2018; originally announced January 2018.

Journal ref: Phys. Rev. A 98, 040301(R) (2018)

Observation of stronger-than-binary correlations with entangled photonic qutrits

Authors: Xiao-Min Hu, Bi-Heng Liu, Yu Guo, Guo-Yong Xiang, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo, Matthias Kleinmann, Tamás Vértesi, Adán Cabello

Abstract: We present the first experimental confirmation of the quantum-mechanical prediction of stronger-than-binary correlations. These are correlations that cannot be explained under the assumption that the occurrence of a particular outcome of an $n \ge 3$-outcome measurement is due to a two-step process in which, in the first step, some classical mechanism precludes $n-2$ of the outcomes and, in the se… ▽ More We present the first experimental confirmation of the quantum-mechanical prediction of stronger-than-binary correlations. These are correlations that cannot be explained under the assumption that the occurrence of a particular outcome of an $n \ge 3$-outcome measurement is due to a two-step process in which, in the first step, some classical mechanism precludes $n-2$ of the outcomes and, in the second step, a binary measurement generates the outcome. Our experiment uses pairs of photonic qutrits distributed between two laboratories, where randomly chosen three-outcome measurements are performed. We report a violation by {9.3} standard deviations of the optimal inequality for nonsignaling binary correlations. △ Less

Submitted 5 May, 2018; v1 submitted 18 December, 2017; originally announced December 2017.

Comments: 5 pages, 2 figures

Journal ref: Phys. Rev. Lett. 120, 180402 (2018)

Deterministic realization of collective measurements via photonic quantum walks

Authors: Zhibo Hou, Jun-Feng Tang, Jiangwei Shang, Huangjun Zhu, Jian Li, Yuan Yuan, Kang-Da Wu, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Collective measurements on identically prepared quantum systems can extract more information than local measurements, thereby enhancing information-processing efficiency. Although this nonclassical phenomenon has been known for two decades, it has remained a challenging task to demonstrate the advantage of collective measurements in experiments. Here we introduce a general recipe for performing de… ▽ More Collective measurements on identically prepared quantum systems can extract more information than local measurements, thereby enhancing information-processing efficiency. Although this nonclassical phenomenon has been known for two decades, it has remained a challenging task to demonstrate the advantage of collective measurements in experiments. Here we introduce a general recipe for performing deterministic collective measurements on two identically prepared qubits based on quantum walks. Using photonic quantum walks, we realize experimentally an optimized collective measurement with fidelity 0.9946 without post selection. As an application, we achieve the highest tomographic efficiency in qubit state tomography to date. Our work offers an effective recipe for beating the precision limit of local measurements in quantum state tomography and metrology. In addition, our study opens an avenue for harvesting the power of collective measurements in quantum information processing and for exploring the intriguing physics behind this power. △ Less

Submitted 17 April, 2018; v1 submitted 27 October, 2017; originally announced October 2017.

Comments: Close to the published version

Journal ref: Nature Communications 9 (1), 1414 (2018)

Experimental cyclic inter-conversion between Coherence and Quantum Correlations

Authors: Kang-Da Wu, Zhibo Hou, Yuan-Yuan Zhao, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Jiajun Ma, Qiong-Yi He, Jayne Thompson, Mile Gu

Abstract: Quantum resource theories seek to quantify sources of non-classicality that bestow quantum technologies their operational advantage. Chief among these are studies of quantum correlations and quantum coherence. The former to isolate non-classicality in the correlations between systems, the latter to capture non-classicality of quantum superpositions within a single physical system. Here we present… ▽ More Quantum resource theories seek to quantify sources of non-classicality that bestow quantum technologies their operational advantage. Chief among these are studies of quantum correlations and quantum coherence. The former to isolate non-classicality in the correlations between systems, the latter to capture non-classicality of quantum superpositions within a single physical system. Here we present a scheme that cyclically inter-converts between these resources without loss. The first stage converts coherence present in an input system into correlations with an ancilla. The second stage harnesses these correlations to restore coherence on the input system by measurement of the ancilla. We experimentally demonstrate this inter-conversion process using linear optics. Our experiment highlights the connection between non-classicality of correlations and non-classicality within local quantum systems, and provides potential flexibilities in exploiting one resource to perform tasks normally associated with the other. △ Less

Submitted 4 October, 2017; originally announced October 2017.

Comments: 8 pages, 4 figures, comments welcome

Journal ref: Phys. Rev. Lett. 121, 050401 (2018)

Quantum gate identification: error analysis, numerical results and optical experiment

Authors: Yuanlong Wang, Qi Yin, Daoyi Dong, Bo Qi, Ian R. Petersen, Zhibo Hou, Hidehiro Yonezawa, Guo-Yong Xiang

Abstract: The identification of an unknown quantum gate is a significant issue in quantum technology. In this paper, we propose a quantum gate identification method within the framework of quantum process tomography. In this method, a series of pure states are inputted to the gate and then a fast state tomography on the output states is performed and the data are used to reconstruct the quantum gate. Our al… ▽ More The identification of an unknown quantum gate is a significant issue in quantum technology. In this paper, we propose a quantum gate identification method within the framework of quantum process tomography. In this method, a series of pure states are inputted to the gate and then a fast state tomography on the output states is performed and the data are used to reconstruct the quantum gate. Our algorithm has computational complexity $O(d^3)$ with the system dimension $d$. The algorithm is compared with maximum likelihood estimation method for the running time, which shows the efficiency advantage of our method. An error upper bound is established for the identification algorithm and the robustness of the algorithm against the purity of input states is also tested. We perform quantum optical experiment on single-qubit Hadamard gate to verify the effectiveness of the identification algorithm. △ Less

Submitted 19 July, 2017; originally announced July 2017.

Comments: 19 pages, 5 figures

Journal ref: Automatica, 2019, Vol. 101, pp. 269-279

Taking tomographic measurements for photonic qubits 88 ns before they are created

Authors: Zhibo Hou, Qi Yin, Chao Zhang, Han-Sen Zhong, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo, Geoff J. Pryde, Anthony Laing

Abstract: We experimentally demonstrate that tomographic measurements can be performed for states of qubits before they are prepared. A variant of the quantum teleportation protocol is used as a channel between two instants in time, allowing measurements for polarisation states of photons to be implemented 88 ns before they are created. Measurement data taken at the early time and later unscrambled accordin… ▽ More We experimentally demonstrate that tomographic measurements can be performed for states of qubits before they are prepared. A variant of the quantum teleportation protocol is used as a channel between two instants in time, allowing measurements for polarisation states of photons to be implemented 88 ns before they are created. Measurement data taken at the early time and later unscrambled according to the results of the protocol's Bell measurements, produces density matrices with an average fidelity of $0.90 \pm 0.01$ against the ideal states of photons created at the later time. Process tomography of the time-reverse quantum channel finds an average process fidelity of $0.84 \pm 0.02$. While our proof-of-principle implementation necessitates some post-selection, the general protocol is deterministic and requires no post-selection to sift desired states and reject a larger ensemble. △ Less

Submitted 30 May, 2017; originally announced May 2017.

Comments: Comments welcome

Experimentally Obtaining Maximal Coherence Via Assisted Distillation Pro cess

Authors: Kang-Da Wu, Zhibo Hou, Han-Sen Zhong, Yuan Yuan, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Quantum coherence, which quantifies the superposition properties of a quantum state, plays an indispensable role in quantum resource theory. A recent theoretical work [Phys. Rev. Lett. \textbf{116}, 070402 (2016)] studied the manipulation of quantum coherence in bipartite or multipartite systems under the protocol Local Incoherent Operation and Classical Communication (LQICC). Here we present the… ▽ More Quantum coherence, which quantifies the superposition properties of a quantum state, plays an indispensable role in quantum resource theory. A recent theoretical work [Phys. Rev. Lett. \textbf{116}, 070402 (2016)] studied the manipulation of quantum coherence in bipartite or multipartite systems under the protocol Local Incoherent Operation and Classical Communication (LQICC). Here we present the first experimental realization of obtaining maximal coherence in assisted distillation protocol based on linear optical system. The results of our work show that the optimal distillable coherence rate can be reached even in one-copy scenario when the overall bipartite qubit state is pure. Moreover, the experiments for mixed states showed that distillable coherence can be increased with less demand than entanglement distillation. Our work might be helpful in the remote quantum information processing and quantum control. △ Less

Submitted 21 February, 2017; originally announced February 2017.

Comments: 7 pages, 5 figures

MSC Class: 81-05

Journal ref: Optica Vol. 4, Issue 4, pp. 454-459 (2017)

Experimental demonstration of wave-particle duality relation based on coherence measure

Authors: Yuan Yuan, Zhibo Hou, Yuan-Yuan Zhao, Han-Sen Zhong, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo

Abstract: Wave-particle duality is a typical example of Bohr's complementarity principle that plays a significant role in quantum mechanics. Previous studies used the visibility of an interference pattern to quantify the wave property and used path information to quantify the particle property. However, coherence is the core and basis of the interference phenomenon. If we could use coherence to characterize… ▽ More Wave-particle duality is a typical example of Bohr's complementarity principle that plays a significant role in quantum mechanics. Previous studies used the visibility of an interference pattern to quantify the wave property and used path information to quantify the particle property. However, coherence is the core and basis of the interference phenomenon. If we could use coherence to characterize the wave property, the understanding of wave-particle duality would be strengthened. A recent theoretical work [Phys. Rev. Lett. 116, 160406 (2016)] found two relations between quantum coherence and path information. Here, we demonstrate the new measure of wave-particle duality based on two kinds of coherence measures quantitatively for the first time. The wave property, quantified by the coherence in the l1-norm measure and the relative entropy measure, can be obtained via tomography of the target state, which is encoded in the path degree of freedom of the photons. The particle property, quantified by the path information, can be obtained via the discrimination of detector states, which is encoded in the polarization degree of freedom of the photons. Our work may deepen people's understanding of coherence and provide a new perspective regarding wave-particle duality. △ Less

Submitted 26 February, 2018; v1 submitted 21 February, 2017; originally announced February 2017.

Journal ref: Optics Express, 26(4), 4470-4478(2018)