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Improved entanglement detection with subspace witnesses

Physical Review A 2020年第1期101卷 012319-012319页

作者： Won Kyu Calvin Sun Alexandre Cooper Paola Cappellaro Research Lab of Electronics and Department of Nuclear Science and Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Institute for Quantum Computing University of Waterloo Waterloo Ontario N2L 3G1 Canada

Entanglement, while being critical in many quantum applications, is difficult to characterize experimentally. While entanglement witnesses based on the fidelity to the target entangled state are efficient detectors of entanglement, they in general underestimate the amount of entanglement due to local unitary errors during state preparation and measurement. Therefore, to detect entanglement more robustly in the presence of such control errors, we introduce a ‘subspace’ witness that detects a broader class of entangled states with strictly larger violation than the conventional state-fidelity witness at the cost of additional measurements, while remaining more efficient with respect to state tomography. We experimentally demonstrate the advantages of the subspace witness by generating and detecting entanglement with a hybrid, two-qubit system composed of electronic spins in diamond. We further extend the notion of the subspace witness to specific genuine multipartite entangled (GME) states detected by the state witness, such as GHZ, W, and Dicke states, and motivate the choice of the metric based on quantum information tasks, such as entanglement-enhanced sensing. In addition, as the subspace witness identifies the many-body coherences of the target entangled state, it facilitates (beyond detection) lower-bound quantification of entanglement via generalized concurrences. We expect that the straightforward and efficient implementation of subspace witnesses would be beneficial in detecting specific GME states in noisy, intermediate-scale quantum processors with a hundred qubits.

关键词： quantum entanglement quantum gates quantum information processing

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A universal quantum gate set for transmon qubits with strong ZZ interactions

arXiv

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arXiv 2021年

作者： Long, Junling Zhao, Tongyu Bal, Mustafa Zhao, Ruichen Barron, George S. Ku, Hsiang-Sheng Howard, Joel A. Wu, Xian McRae, Corey Rae H. Deng, Xiu-Hao Ribeill, Guilhem J. Singh, Meenakshi Ohki, Thomas A. Barnes, Edwin Economou, Sophia E. Pappas, David P. Department of Physics University of Colorado BoulderCO80309 United States Department of Physics Virginia Tech BlacksburgVA24061 United States National Institute of Standards and Technology BoulderCO80305 United States Department of Physics Colorado School of Mines GoldenCO80401 United States Shenzhen Institute of Quantum Science and Engineering Southern University of Science and Technology Shenzhen Guangdong518055 China Quantum Engineering and Computing Raytheon BBN Technologies CambridgeMA02138 United States

High-fidelity single- and two-qubit gates are essential building blocks for a fault-tolerant quantum computer. While there has been much progress in suppressing single-qubit gate errors in superconducting qubit systems, two-qubit gates still suffer from error rates that are orders of magnitude higher. One limiting factor is the residual ZZ-interaction, which originates from a coupling between computational states and higher-energy states. While this interaction is usually viewed as a nuisance, here we experimentally demonstrate that it can be exploited to produce a universal set of fast single- and two-qubit entangling gates in a coupled transmon qubit system. To implement arbitrary single-qubit rotations, we design a new protocol called the two-axis gate that is based on a three-part composite pulse. It rotates a single qubit independently of the state of the other qubit despite the strong ZZ-coupling. We achieve single-qubit gate fidelities as high as 99.1% (for |g01i ↔ |g11i transition) from randomized benchmarking measurements. We then demonstrate both a CZ gate and a CNOT gate. Because the system has a strong ZZ-interaction, a CZ gate can be achieved by letting the system freely evolve for a gate time tg = 53.8 ns. To design the CNOT gate, we utilize an analytical microwave pulse shape based on the SWIPHT protocol for realizing fast, low-leakage gates. We obtain fidelities of 94.6% and 97.8% for the CNOT and CZ gates respectively from quantum progress tomography. Copyright © 2021, The Authors. All rights reserved.

关键词： Logic gates

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Erratum to: Noisy intermediate-scale quantum computers

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Frontiers of Physics 2024年第4期19卷 1-1页

作者： Cheng, Bin Deng, Xiu-Hao Gu, Xiu He, Yu Hu, Guangchong Huang, Peihao Li, Jun Lin, Ben-Chuan Lu, Dawei Lu, Yao Qiu, Chudan Wang, Hui Xin, Tao Yu, Shi Yung, Man-Hong Zeng, Junkai Zhang, Song Zhong, Youpeng Peng, Xinhua Nori, Franco Yu, Dapeng Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen China International Quantum Academy Shenzhen China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen China Department of Physics Southern University of Science and Technology Shenzhen China Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences University of Science and Technology of China Hefei China CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Hefei China Hefei National Laboratory University of Science and Technology of China Hefei China CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences University of Science and Technology of China Hefei China Quantum Computing Center and Cluster for Pioneering Research RIKEN Wakoshi Saitama Japan Physics Department University of Michigan Ann Arbor USA

In the original article, we have identified an inappropriate reference in the citation section of the context. To ensure the academic rigor and accuracy of the article, we decided to replace a reference with the new o...

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Multivariate bicycle codes

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Physical Review A 2025年第6期111卷 L060401-L060401页

作者： Lukas Voss Sim Jian Xian Tobias Haug Kishor Bharti Institute of Theoretical Physics and IQST Ulm University Albert-Einstein-Allee 11 D-89069 Ulm Germany Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 Singapore 117543 Yale-NUS College Singapore ASTAR Quantum Innovation Centre Institute of High Performance Computing Agency for Science Technology and Research 1 Fusionopolis Way 16-16 Connexis Singapore 138632 Republic of Singapore Quantum Research Center Technology Innovation Institute Abu Dhabi United Arab Emirates Centre for Quantum Engineering Research and Education TCG CREST Sector V Salt Lake Kolkata 700091 India Science Mathematics and Technology Cluster Singapore University of Technology and Design 8 Somapah Road Singapore 487372 Singapore

quantum error correction suppresses noise in quantum systems to allow for high-precision computations. In this Letter, we introduce multivariate bicycle quantum low-density parity-check (QLDPC) codes, via an extension of the framework developed by Bravyi et al. [S. Bravyi, A. W. Cross, J. M. Gambetta, D. Maslov, P. Rall, and T. J. Yoder, Nature (London) 627, 778 (2024)], and particularly focus on trivariate bicycle (TB) codes. Unlike the weight-6 codes proposed in their study, we offer concrete examples of weight-5 TB-QLDPC codes which promise to be more amenable to near-term experimental setups. We show that TB-QLDPC codes up to weight 6 have a biplanar structure and often possess a two-dimensional toric layout. Under circuit level noise, we find substantially better encoding rates than comparable surface codes while offering similar error suppression capabilities. For example, we can encode four logical qubits with distance 5 into 60 physical qubits using weight-5 check measurements of circuit depth 7, while a surface code with these parameters requires 200 physical qubits. The high encoding rate and compact layout make our codes highly suitable candidates for near-term hardware implementations, paving the way for a realizable quantum error correction protocol.

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Topological Spin Texture of Chiral Edge States in Photonic Two-Dimensional quantum Walks

arXiv

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arXiv 2021年

作者： Chen, Chao Ding, Xing Qin, Jian Wu, Jizhou He, Yu Lu, Chao-Yang Li, Li Liu, Xiong-Jun Sanders, Barry C. Pan, Jian-Wei Hefei National Laboratory for Physical Sciences at the Microscale Department of Modern Physics University of Science and Technology of China Shanghai Branch Shanghai201315 China CAS-Alibaba Quantum Computing Laboratory CAS Centre for Excellence in Quantum Information and Quantum Physics Shanghai201315 China National Laboratory of Solid State Microstructures School of Physics Nanjing University Nanjing210093 China Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Institute for Quantum Science and Technology University of Calgary ABT2N 1N4 Canada

Topological insulators host topology-linked boundary states, whose spin and charge degrees of freedom could be exploited to design topological devices with enhanced functionality. We experimentally observe that dissipationless chiral edge states in a spin-orbit coupled anomalous Floquet topological phase exhibit topological spin texture on boundaries, realized via a two-dimensional quantum walk. Our experiment shows that, for a walker traveling around a closed loop along the boundary in real space, its spin evolves and winds through a great circle on the Bloch sphere, which implies that edge-spin texture has nontrivial winding. This topological spin winding is protected by a chiral-like symmetry emerging for the low-energy Hamiltonian. Our experiment confirms that two-dimensional anomalous Floquet topological systems exhibit topological spin texture on the boundary, which could inspire novel topology-based spintronic phenomena and devices. Copyright © 2021, The Authors. All rights reserved.

关键词： Topology

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Acousto-drag photovoltaic effect by piezoelectric integration of two-dimensional semiconductors

arXiv

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arXiv 2023年

作者： Gu, Jiaming Mou, Yicheng Ma, Jianwen Chen, Haonan Zhang, Chuanxin Wang, Yuxiang Wang, Jiayu Guo, Hangwen Shi, Wu Yuan, Xiang Jiang, Xue Ta, Dean Shen, Jian Zhang, Cheng State Key Laboratory of Surface Physics Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai200433 China Center for Biomedical Engineering School of Information Science and Technology Fudan University Shanghai200433 China Zhangjiang Fudan International Innovation Center Fudan University Shanghai201210 China Shanghai Qi Zhi Institute Shanghai200232 China State Key Laboratory of Precision Spectroscopy East China Normal University Shanghai200241 China School of Physics and Electronic Science East China Normal University Shanghai200241 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China

Light-to-electricity conversion is crucial for energy harvesting and photodetection, requesting efficient electron-hole pair separation to prevent recombination. Traditional junction-based mechanisms using built-in electric fields fail in non-barrier regions. Homogeneous material harvesting under photovoltaic effect is appealing but only realized in non-centrosymmetric systems via bulk photovoltaic effect. Here we report the realization of photovoltaic effect by employing surface acoustic waves (SAW) to generate zero-bias photocurrent in a conventional layered semiconductor MoSe2. SAW induces periodic modulation to electronic bands and drags the photoexcited pairs toward the travelling direction. The photocurrent is extracted by a local barrier. The separation of generation and extraction processes suppresses recombination and yields large nonlocal photoresponse. We distinguish acousto-electric drag and electron-hole pair separation effect by fabricating devices of different configurations. The acousto-drag photovoltaic effect, enabled by piezoelectric integration, offers an efficient light-to-electricity conversion method, independent of semiconductor crystal symmetry. © 2023, CC BY.

关键词： Energy harvesting

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Exact distributed quantum algorithm for generalized Simon’s problem

arXiv

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arXiv 2023年

作者： Li, Hao Qiu, Daowen Luo, Le Mateus, Paulo Institute of Quantum Computing and Computer Theory School of Computer Science and Engineering Sun Yat-sen University Guangzhou510006 China The Guangdong Key Laboratory of Information Security Technology Sun Yat-sen University 510006 China QUDOOR Technologies Inc. Zhuhai China School of Physics and Astronomy Sun Yat-sen University Zhuhai519082 China Instituto de Telecomunicações Departamento de Matemática Instituto Superior Técnico Av. Rovisco Pais Lisbon1049-001 Portugal

Simon’s problem is one of the most important problems demonstrating the power of quantum algorithms, as it greatly inspired the proposal of Shor’s algorithm. The generalized Simon’s problem is a natural extension of Simon’s problem, and also a special hidden subgroup problem: Given a function f : {0, 1}n → {0, 1}m, with the property that for any x, y ∈ {0, 1}n, there is some unknown hidden subgroup S ≤ 2n such that f(x) = f(y) iff x ⊕ y ∈ S, where |S| = 2k for some 0 ≤ k ≤ n (m ≥ n − k). The goal of generalized Simon’s problem is to find the hidden subgroup S. In this paper, we present two key contributions. Firstly, we characterize the structure of the generalized Simon’s problem in distributed scenario and introduce a corresponding distributed quantum algorithm. Secondly, we refine the algorithm to ensure exactness due to the application of quantum amplitude amplification technique. Our algorithm offers exponential acceleration compared to the distributed classical algorithm. When contrasted with the centralized quantum algorithm for the generalized Simon’s problem, our algorithm’s oracle requires fewer qubits, thus making it easier to be physically implemented. Particularly, the exact distributed quantum algorithm we develop for the generalized Simon’s problem outperforms the best previously proposed distributed quantum algorithm for Simon’s problem in terms of generalizability and exactness. Copyright © 2023, The Authors. All rights reserved.

关键词： Qubits

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RECOMED: A Comprehensive Pharmaceutical Recommendation System

arXiv

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arXiv 2022年

作者： Zomorodi, Mariam Ghodsollahee, Ismail Martin, Jennifer H. Talley, Nicholas J. Salari, Vahid Plawiak, Pawel Rahimi, Kazem Acharya, U. Rajendra Department of Computer Science Faculty of Computer Science and Telecommunications Cracow University of Technology Krakow Poland Department of Computer Engineering Ferdowsi University of Mashhad Iran The University of Newcastle CallaghanNSW Australia Institute for Quantum Science and Technology Department of Physics and Astronomy University of Calgary Alberta Canada Institute of Theoretical and Applied Informatics Polish Academy of Sciences Gliwice Poland Deep Medicine Nuffield Department of Women’s and Reproductive Health University of Oxford Oxford United Kingdom School of Mathematics Physics and Computing University of Southern Queensland ToowoombaQLD Australia

OBJECTIVES: To build datasets containing useful information from drug databases and recommend a list of drugs to physicians and patients with high accuracy by considering features of a spectrum of people, diseases, and chemicals. METHODS: A comprehensive pharmaceutical recommendation system was designed based on the features of a spectrum of people, diseases, and medicines extracted from two major drug databases, a dataset of patients and drug information. Then the recommendation was given, and the response was analysed using patient and caregiver ratings and the knowledge obtained from drug specifications and interactions. Sentiment analysis was employed by natural language processing approaches in pre-processing, along with neural network-based methods and recommender system algorithms for modelling the system. Patient conditions and medicine features were used for making two models based on matrix factorisation. Then we used drug interaction criteria to filter drugs with severe or mild interactions with other drugs. We developed a deep learning model for recommending drugs by using data from 2304 patients as a training set, and then we used data from 660 patients as our validation set. We used knowledge from critical drug information and combined the model’s outcome into a knowledge-based system with the rules obtained from constraints on taking medicine. RESULTS: The results show that our recommendation system can recommend an acceptable combination of medicines according to the existing real-life prescriptions available. Compared with conventional matrix factorisation, our proposed model improves the accuracy, sensitivity, and hit rate by 26%, 34%, and 40%, respectively. In addition, it improves the accuracy, sensitivity, and hit rate by an average of 31%, 29%, and 28% compared to other machine learning methods. We have open-sourced our implementation in Python. CONCLUSION: Compared to conventional machine learning approaches, we obtained average accuracy, sens

关键词： Recommender systems

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Dynamic Kosterlitz-Thouless theory for two-dimensional ultracold atomic gases

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Physical Review A 2020年第4期102卷 043311-043311页

作者： Zhigang Wu Shizhong Zhang Hui Zhai Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 Guangdong China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 Guangdong China Department of Physics and HKU-UCAS Joint Institute for Theoretical and Computational Physics at Hong Kong University of Hong Kong Hong Kong China Institute for Advanced Study Tsinghua University Beijing 100084 China Center for Quantum Computing Peng Cheng Laboratory Shenzhen 518055 China

In this paper we develop a theory for the first and second sounds in a two-dimensional atomic gas across the superfluid transition based on the dynamic Koterlitz-Thouless theory. We employ a set of modified two-fluid hydrodynamic equations which incorporate the dynamics of the quantized vortices, rather than the conventional ones for a three-dimensional superfluid. As far as the sound dispersion equation is concerned, the modification is essentially equivalent to replacing the static superfluid density with a frequency-dependent one, renormalized by the frequency-dependent “dielectric constant” of the vortices. This theory has two direct consequences. First, because the renormalized superfluid density at finite frequencies does not display discontinuity across the superfluid transition, in contrast to the static superfluid density, the sound velocities vary smoothly across the transition. Second, the theory includes dissipation due to free vortices and thus naturally describes the sound-to-diffusion crossover for the second sound in the normal phase. With only one fitting parameter, our theory gives a perfect agreement with the experimental measurements of sound velocities across the transition, as well as the quality factor in the vicinity of the transition. The predictions from this theory can be further verified by future experiments.

关键词： BKT transition Bose-Einstein condensates Cold atoms & matter waves Superfluidity Vortices in superfluids

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Queue-channel capacities with generalized amplitude damping

arXiv

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arXiv 2021年

作者： Siddhu, Vikesh Chatterjee, Avhishek Jagannathan, Krishna Mandayam, Prabha Tayur, Sridhar JILA University of Colorado/NIST 440 UCB BoulderCO80309 United States Department of Electrical Engineering Indian Institute of Technology Madras Chennai600036 India Department of Physics Indian Institute of Technology Madras Chennai600036 India Quantum Computing Group Tepper School of Business Carnegie Mellon University PittsburghPA15213 United States

The generalized amplitude damping channel (GADC) is considered an important model for quantum communications, especially over optical networks. We make two salient contributions in this paper apropos of this channel. First, we consider a symmetric GAD channel characterized by the parameter n = 1/2, and derive its exact classical capacity, by constructing a specific induced classical channel. We show that the Holevo quantity for the GAD channel equals the Shannon capacity of the induced binary symmetric channel, establishing at once the capacity result and that theGADchannel capacity can be achieved without the use of entanglement at the encoder or joint measurements at the decoder. Second, motivated by the inevitable buffering of qubits in quantum networks, we consider a generalized amplitude damping queuechannel-that is, a setting where qubits suffer a waiting time dependent GAD noise as they wait in a buffer to be transmitted. This GAD queue channel is characterized by non-i.i.d. noise due to correlated waiting times of consecutive qubits. We exploit a conditional independence property in conjunction with additivity of the channel model, to obtain a capacity expression for the GAD queue channel in terms of the stationary waiting time in the queue. Our results provide useful insights towards designing practical quantum communication networks, and highlight the need to explicitly model the impact of buffering. Copyright © 2021, The Authors. All rights reserved.

关键词： quantum entanglement

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