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The nonequilibrium cost of accurate information processing. Nat Commun 2022; 13:7155. [DOI: 10.1038/s41467-022-34541-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 10/28/2022] [Indexed: 11/24/2022] Open
Abstract
AbstractAccurate information processing is crucial both in technology and in nature. To achieve it, any information processing system needs an initial supply of resources away from thermal equilibrium. Here we establish a fundamental limit on the accuracy achievable with a given amount of nonequilibrium resources. The limit applies to arbitrary information processing tasks and arbitrary information processing systems subject to the laws of quantum mechanics. It is easily computable and is expressed in terms of an entropic quantity, which we name the reverse entropy, associated to a time reversal of the information processing task under consideration. The limit is achievable for all deterministic classical computations and for all their quantum extensions. As an application, we establish the optimal tradeoff between nonequilibrium and accuracy for the fundamental tasks of storing, transmitting, cloning, and erasing information. Our results set a target for the design of new devices approaching the ultimate efficiency limit, and provide a framework for demonstrating thermodynamical advantages of quantum devices over their classical counterparts.
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2
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Ma L, Lei X, Yan J, Li R, Chai T, Yan Z, Jia X, Xie C, Peng K. High-performance cavity-enhanced quantum memory with warm atomic cell. Nat Commun 2022; 13:2368. [PMID: 35501315 PMCID: PMC9061733 DOI: 10.1038/s41467-022-30077-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Accepted: 04/14/2022] [Indexed: 11/09/2022] Open
Abstract
AbstractHigh-performance quantum memory for quantized states of light is a prerequisite building block of quantum information technology. Despite great progresses of optical quantum memories based on interactions of light and atoms, physical features of these memories still cannot satisfy requirements for applications in practical quantum information systems, since all of them suffer from trade-off between memory efficiency and excess noise. Here, we report a high-performance cavity-enhanced electromagnetically-induced-transparency memory with warm atomic cell in which a scheme of optimizing the spatial and temporal modes based on the time-reversal approach is applied. The memory efficiency up to 67 ± 1% is directly measured and a noise level close to quantum noise limit is simultaneously reached. It has been experimentally demonstrated that the average fidelities for a set of input coherent states with different phases and amplitudes within a Gaussian distribution have exceeded the classical benchmark fidelities. Thus the realized quantum memory platform has been capable of preserving quantized optical states, and is ready to be applied in quantum information systems, such as distributed quantum logic gates and quantum-enhanced atomic magnetometry.
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3
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Wu YD, Bai G, Chiribella G, Liu N. Efficient Verification of Continuous-Variable Quantum States and Devices without Assuming Identical and Independent Operations. PHYSICAL REVIEW LETTERS 2021; 126:240503. [PMID: 34213942 DOI: 10.1103/physrevlett.126.240503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Accepted: 05/18/2021] [Indexed: 06/13/2023]
Abstract
Continuous-variable quantum information, encoded into infinite-dimensional quantum systems, is a promising platform for the realization of many quantum information protocols, including quantum computation, quantum metrology, quantum cryptography, and quantum communication. To successfully demonstrate these protocols, an essential step is the certification of multimode continuous-variable quantum states and quantum devices. This problem is well studied under the assumption that multiple uses of the same device result in identical and independently distributed (i.i.d.) operations. However, in realistic scenarios, identical and independent state preparation and calls to the quantum devices cannot be generally guaranteed. Important instances include adversarial scenarios and instances of time-dependent and correlated noise. In this Letter, we propose the first set of reliable protocols for verifying multimode continuous-variable entangled states and devices in these non-i.i.d scenarios. Although not fully universal, these protocols are applicable to Gaussian quantum states, non-Gaussian hypergraph states, as well as amplification, attenuation, and purification of noisy coherent states.
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Affiliation(s)
- Ya-Dong Wu
- QICI Quantum Information and Computation Initiative, Department of Computer Science, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Ge Bai
- QICI Quantum Information and Computation Initiative, Department of Computer Science, The University of Hong Kong, Pokfulam Road, Hong Kong
| | - Giulio Chiribella
- QICI Quantum Information and Computation Initiative, Department of Computer Science, The University of Hong Kong, Pokfulam Road, Hong Kong
- The University of Hong Kong Shenzhen Institute of Research and Innovation, 5/F, Key Laboratory Platform Building, No. 6, Yuexing 2nd Road, Nanshan, Shenzhen 518057, China
- Department of Computer Science, Parks Road, Oxford OX1 3QD, United Kingdom
- Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada
| | - Nana Liu
- Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240, China
- Ministry of Education, Key Laboratory in Scientific and Engineering Computing, Shanghai Jiao Tong University, Shanghai 200240, China
- University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai 200240, China
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4
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Liang YC, Yeh YH, Mendonça PEMF, Teh RY, Reid MD, Drummond PD. Quantum fidelity measures for mixed states. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2019; 82:076001. [PMID: 31022705 DOI: 10.1088/1361-6633/ab1ca4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Applications of quantum technology often require fidelities to quantify performance. These provide a fundamental yardstick for the comparison of two quantum states. While this is straightforward in the case of pure states, it is much more subtle for the more general case of mixed quantum states often found in practice. A large number of different proposals exist. In this review, we summarize the required properties of a quantum fidelity measure, and compare them, to determine which properties each of the different measures has. We show that there are large classes of measures that satisfy all the required properties of a fidelity measure, just as there are many norms of Hilbert space operators, and many measures of entropy. We compare these fidelities, with detailed proofs of their properties. We also summarize briefly the applications of these measures in teleportation, quantum memories and quantum computers, quantum communications, and quantum phase-space simulations.
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Affiliation(s)
- Yeong-Cherng Liang
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan. Center for Quantum Frontiers of Research & Technology (QFort), National Cheng Kung University, Tainan 701, Taiwan
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5
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Bai G, Chiribella G. Test One to Test Many: A Unified Approach to Quantum Benchmarks. PHYSICAL REVIEW LETTERS 2018; 120:150502. [PMID: 29756868 DOI: 10.1103/physrevlett.120.150502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Indexed: 06/08/2023]
Abstract
Quantum benchmarks are routinely used to validate the experimental demonstration of quantum information protocols. Many relevant protocols, however, involve an infinite set of input states, of which only a finite subset can be used to test the quality of the implementation. This is a problem, because the benchmark for the finitely many states used in the test can be higher than the original benchmark calculated for infinitely many states. This situation arises in the teleportation and storage of coherent states, for which the benchmark of 50% fidelity is commonly used in experiments, although finite sets of coherent states normally lead to higher benchmarks. Here, we show that the average fidelity over all coherent states can be indirectly probed with a single setup, requiring only two-mode squeezing, a 50-50 beam splitter, and homodyne detection. Our setup enables a rigorous experimental validation of quantum teleportation, storage, amplification, attenuation, and purification of noisy coherent states. More generally, we prove that every quantum benchmark can be tested by preparing a single entangled state and measuring a single observable.
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Affiliation(s)
- Ge Bai
- Department of Computer Science, The University of Hong Kong, Pokfulam Road, Hong Kong 999077, China and HKU Shenzhen Institute of Research and Innovation, Yuexing 2nd Rd Nanshan, Shenzhen 518057, China
| | - Giulio Chiribella
- Department of Computer Science, University of Oxford, Wolfson Building, Parks Road, Oxford OX1 3QD, United Kingdom and CIFAR Program in Quantum Information Science, Canadian Institute for Advanced Research, Toronto, Ontario ON M5G 1Z8, Canada
- Department of Computer Science, The University of Hong Kong, Pokfulam Road, Hong Kong 999077, China and HKU Shenzhen Institute of Research and Innovation, Yuexing 2nd Rd Nanshan, Shenzhen 518057, China
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6
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Liuzzo-Scorpo P, Mari A, Giovannetti V, Adesso G. Optimal Continuous Variable Quantum Teleportation with Limited Resources. PHYSICAL REVIEW LETTERS 2017; 119:120503. [PMID: 29341664 DOI: 10.1103/physrevlett.119.120503] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Indexed: 06/07/2023]
Abstract
Given a certain amount of entanglement available as a resource, what is the most efficient way to accomplish a quantum task? We address this question in the relevant case of continuous variable quantum teleportation protocols implemented using two-mode Gaussian states with a limited degree of entanglement and energy. We first characterize the class of single-mode phase-insensitive Gaussian channels that can be simulated via a Braunstein-Kimble protocol with nonunit gain and minimum shared entanglement, showing that infinite energy is not necessary apart from the special case of the quantum limited attenuator. We also find that apart from the identity, all phase-insensitive Gaussian channels can be simulated through a two-mode squeezed state with finite energy, albeit with a larger entanglement. We then consider the problem of teleporting single-mode coherent states with Gaussian-distributed displacement in phase space. Performing a geometrical optimization over phase-insensitive Gaussian channels, we determine the maximum average teleportation fidelity achievable with any finite entanglement and for any realistically finite variance of the input distribution.
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Affiliation(s)
- Pietro Liuzzo-Scorpo
- Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems (CQNE), School of Mathematical Sciences, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Andrea Mari
- NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56127 Pisa, Italy
| | - Vittorio Giovannetti
- NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, I-56127 Pisa, Italy
| | - Gerardo Adesso
- Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems (CQNE), School of Mathematical Sciences, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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7
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He Q, Rosales-Zárate L, Adesso G, Reid MD. Secure Continuous Variable Teleportation and Einstein-Podolsky-Rosen Steering. PHYSICAL REVIEW LETTERS 2015; 115:180502. [PMID: 26565449 DOI: 10.1103/physrevlett.115.180502] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Indexed: 06/05/2023]
Abstract
We investigate the resources needed for secure teleportation of coherent states. We extend continuous variable teleportation to include quantum teleamplification protocols that allow nonunity classical gains and a preamplification or postattenuation of the coherent state. We show that, for arbitrary Gaussian protocols and a significant class of Gaussian resources, two-way steering is required to achieve a teleportation fidelity beyond the no-cloning threshold. This provides an operational connection between Gaussian steerability and secure teleportation. We present practical recipes suggesting that heralded noiseless preamplification may enable high-fidelity heralded teleportation, using minimally entangled yet steerable resources.
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Affiliation(s)
- Qiongyi He
- State Key Laboratory of Mesoscopic Physics, School of Physics, Peking University, Collaborative Innovation Center of Quantum Matter, Beijing 100871 China
- Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia
| | - Laura Rosales-Zárate
- Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia
| | - Gerardo Adesso
- School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Margaret D Reid
- Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia
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8
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Namiki R, Azuma K. Quantum benchmark via an uncertainty product of canonical variables. PHYSICAL REVIEW LETTERS 2015; 114:140503. [PMID: 25910100 DOI: 10.1103/physrevlett.114.140503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Indexed: 06/04/2023]
Abstract
We present an uncertainty-relation-type quantum benchmark for continuous-variable (CV) quantum channels that works with an input ensemble of Gaussian-distributed coherent states and homodyne measurements. It determines an optimal trade-off relation between canonical quadrature noises that is unbeatable by entanglement breaking channels and refines the notion of two quantum duties introduced in the original papers of CV quantum teleportation. This benchmark can verify the quantum-domain performance for all one-mode Gaussian channels. We also address the case of stochastic channels and the effect of asymmetric gains.
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Affiliation(s)
- Ryo Namiki
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada
| | - Koji Azuma
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
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9
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He QY, Gong QH, Reid MD. Classifying directional Gaussian entanglement, Einstein-Podolsky-Rosen steering, and discord. PHYSICAL REVIEW LETTERS 2015; 114:060402. [PMID: 25723192 DOI: 10.1103/physrevlett.114.060402] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Indexed: 06/04/2023]
Abstract
Using Venn diagrams, we classify the different types of two-mode Gaussian continuous variable quantum correlation including directional entanglement and Einstein-Podolsky-Rosen (EPR) steering. We establish unified signatures for one- and two-way quantum steering, entanglement, and discord beyond entanglement in terms of an EPR-type variance. By focusing on Gaussian states, we link an optimized condition for entanglement based on an EPR variance to the Simon-Peres condition. This allows us to quantify the asymmetry of the Gaussian entanglement, and to relate the asymmetry to a directional quantum teleportation protocol where Alice and Bob possess asymmetrically noisy channels. Our analysis enables a determination of the type and direction of quantum correlation in a way that is easily measured in experiment. We also find that for symmetric states, when discord exceeds a certain threshold, the states are necessarily steerable.
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Affiliation(s)
- Q Y He
- State Key Laboratory of Mesoscopic Physics, School of Physics, Peking University, Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Q H Gong
- State Key Laboratory of Mesoscopic Physics, School of Physics, Peking University, Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - M D Reid
- Centre for Quantum Atom Optics, Swinburne University of Technology, Melbourne, Australia
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10
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Chiribella G, Adesso G. Quantum benchmarks for pure single-mode Gaussian states. PHYSICAL REVIEW LETTERS 2014; 112:010501. [PMID: 24483875 DOI: 10.1103/physrevlett.112.010501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Indexed: 06/03/2023]
Abstract
Teleportation and storage of continuous variable states of light and atoms are essential building blocks for the realization of large-scale quantum networks. Rigorous validation of these implementations require identifying, and surpassing, benchmarks set by the most effective strategies attainable without the use of quantum resources. Such benchmarks have been established for special families of input states, like coherent states and particular subclasses of squeezed states. Here we solve the longstanding problem of defining quantum benchmarks for general pure Gaussian single-mode states with arbitrary phase, displacement, and squeezing, randomly sampled according to a realistic prior distribution. As a special case, we show that the fidelity benchmark for teleporting squeezed states with totally random phase and squeezing degree is 1/2, equal to the corresponding one for coherent states. We discuss the use of entangled resources to beat the benchmarks in experiments.
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Affiliation(s)
- Giulio Chiribella
- Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, China
| | - Gerardo Adesso
- School of Mathematical Sciences, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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11
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Chiribella G, Xie J. Optimal design and quantum benchmarks for coherent state amplifiers. PHYSICAL REVIEW LETTERS 2013; 110:213602. [PMID: 23745872 DOI: 10.1103/physrevlett.110.213602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/31/2013] [Indexed: 06/02/2023]
Abstract
We establish the ultimate quantum limits to the amplification of an unknown coherent state, both in the deterministic and probabilistic case, investigating the realistic scenario where the expected photon number is finite. In addition, we provide the benchmark that experimental realizations have to surpass in order to beat all classical amplification strategies and to demonstrate genuine quantum amplification. Our result guarantees that a successful demonstration is in principle possible for every finite value of the expected photon number.
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Affiliation(s)
- Giulio Chiribella
- Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, China.
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12
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Nha H, Lee SY, Ji SW, Kim MS. Efficient entanglement criteria beyond Gaussian limits using Gaussian measurements. PHYSICAL REVIEW LETTERS 2012; 108:030503. [PMID: 22400723 DOI: 10.1103/physrevlett.108.030503] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Indexed: 05/31/2023]
Abstract
We present a formalism to derive entanglement criteria beyond the Gaussian regime that can be readily tested by only homodyne detection. The measured observable is the Einstein-Podolsky-Rosen (EPR) correlation. Its arbitrary functional form enables us to detect non-Gaussian entanglement even when an entanglement test based on second-order moments fails. We illustrate the power of our experimentally friendly criteria for a broad class of non-Gaussian states under realistic conditions. We also show rigorously that quantum teleportation for continuous variables employs a specific functional form of EPR correlation.
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Affiliation(s)
- Hyunchul Nha
- Department of Physics, Texas A & M University at Qatar, PO Box 23874, Doha, Qatar.
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13
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Lobino M, Kupchak C, Figueroa E, Lvovsky AI. Memory for light as a quantum process. PHYSICAL REVIEW LETTERS 2009; 102:203601. [PMID: 19519026 DOI: 10.1103/physrevlett.102.203601] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2008] [Indexed: 05/27/2023]
Abstract
We report complete characterization of an optical memory based on electromagnetically induced transparency. We recover the superoperator associated with the memory, under two different working conditions, by means of a quantum process tomography technique that involves storage of coherent states and their characterization upon retrieval. In this way, we can predict the quantum state retrieved from the memory for any input, for example, the squeezed vacuum or the Fock state. We employ the acquired superoperator to verify the nonclassicality benchmark for the storage of a Gaussian distributed set of coherent states.
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Affiliation(s)
- M Lobino
- Institute for Quantum Information Science, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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14
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Namiki R, Koashi M, Imoto N. Fidelity criterion for quantum-domain transmission and storage of coherent states beyond the unit-gain constraint. PHYSICAL REVIEW LETTERS 2008; 101:100502. [PMID: 18851198 DOI: 10.1103/physrevlett.101.100502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2007] [Revised: 04/23/2008] [Indexed: 05/26/2023]
Abstract
We generalize the experimental success criterion for quantum teleportation (memory) in continuous-variable quantum systems to be suitable for a non-unit-gain condition by considering attenuation (amplification) of the coherent-state amplitude. The new criterion can be used for a nonideal quantum memory and long distance quantum communication as well as quantum devices with amplification process. It is also shown that the framework to measure the average fidelity is capable of detecting all Gaussian channels in the quantum domain.
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Affiliation(s)
- Ryo Namiki
- CREST Research Team for Photonic Quantum Information, Division of Materials Physics, Department of Materials Engineering Science, Graduate school of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
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15
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Adesso G, Chiribella G. Quantum benchmark for teleportation and storage of squeezed states. PHYSICAL REVIEW LETTERS 2008; 100:170503. [PMID: 18518264 DOI: 10.1103/physrevlett.100.170503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Indexed: 05/26/2023]
Abstract
We provide a quantum benchmark for teleportation and storage of single-mode squeezed states with zero displacement and a completely unknown degree of squeezing along a given direction. For pure squeezed input states, a fidelity higher than 81.5% has to be attained in order to outperform any classical strategy based on an estimation of the unknown squeezing and repreparation of squeezed states. For squeezed thermal input states, we derive an upper and a lower bound on the classical average fidelity which tighten for moderate degree of mixedness. These results enable a critical discussion of recent experiments with squeezed light.
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Affiliation(s)
- Gerardo Adesso
- Dipartimento di Matematica e Informatica, Universitá degli Studi di Salerno, Via Ponte Don Melillo, 84084 Fisciano (SA), Italy
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16
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Hétet G, Longdell JJ, Alexander AL, Lam PK, Sellars MJ. Electro-optic quantum memory for light using two-level atoms. PHYSICAL REVIEW LETTERS 2008; 100:023601. [PMID: 18232866 DOI: 10.1103/physrevlett.100.023601] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Indexed: 05/25/2023]
Abstract
We present a simple quantum memory scheme that allows for the storage of a light field in an ensemble of two-level atoms. The technique is analogous to the NMR gradient echo for which the imprinting and recalling of the input field are performed by controlling a linearly varying broadening. Our protocol is perfectly efficient in the limit of high optical depths and the output pulse is emitted in the forward direction. We provide a numerical analysis of the protocol together with an experiment performed in a solid state system. In close agreement with our model, the experiment shows a total efficiency of up to 15%, and a recall efficiency of 26%. We suggest simple realizable improvements for the experiment to surpass the no-cloning limit.
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Affiliation(s)
- G Hétet
- ARC COE for Quantum-Atom Optics, Australian National University, Canberra, ACT 0200, Australia
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17
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Yonezawa H, Braunstein SL, Furusawa A. Experimental demonstration of quantum teleportation of broadband squeezing. PHYSICAL REVIEW LETTERS 2007; 99:110503. [PMID: 17930422 DOI: 10.1103/physrevlett.99.110503] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Indexed: 05/25/2023]
Abstract
We demonstrate an unconditional high-fidelity teleporter capable of preserving the broadband entanglement in an optical squeezed state. In particular, we teleport a squeezed state of light and observe -0.8+/-0.2 dB of squeezing in the teleported (output) state. We show that the squeezing criterion translates directly into a sufficient criterion for entanglement of the upper and lower sidebands of the optical field. Thus, this result demonstrates the first unconditional teleportation of broadband entanglement. Our teleporter achieves sufficiently high fidelity to allow the teleportation to be cascaded, enabling, in principle, the construction of deterministic non-Gaussian operations.
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Affiliation(s)
- Hidehiro Yonezawa
- Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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18
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Niset J, Acín A, Andersen UL, Cerf NJ, García-Patrón R, Navascués M, Sabuncu M. Superiority of entangled measurements over all local strategies for the estimation of product coherent states. PHYSICAL REVIEW LETTERS 2007; 98:260404. [PMID: 17678072 DOI: 10.1103/physrevlett.98.260404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Indexed: 05/16/2023]
Abstract
It is shown that the ensemble {P(alpha),|alpha|alpha;{*}}, where P(alpha) is a Gaussian distribution of finite variance and |alpha is a coherent state, can be better discriminated with an entangled measurement than with any local strategy supplemented by classical communication. Although this ensemble consists of products of quasiclassical states without any squeezing, it thus exhibits a purely quantum feature. This remarkable effect is demonstrated experimentally by implementing the optimal local strategy on coherent states of light together with a global strategy that yields a higher fidelity.
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Affiliation(s)
- J Niset
- Quantum Information and Communication, Ecole Polytechnique, CP 165, Université Libre de Bruxelles, 1050 Brussels, Belgium
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Sherson JF, Krauter H, Olsson RK, Julsgaard B, Hammerer K, Cirac I, Polzik ES. Quantum teleportation between light and matter. Nature 2006; 443:557-60. [PMID: 17024089 DOI: 10.1038/nature05136] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2006] [Accepted: 07/28/2006] [Indexed: 11/09/2022]
Abstract
Quantum teleportation is an important ingredient in distributed quantum networks, and can also serve as an elementary operation in quantum computers. Teleportation was first demonstrated as a transfer of a quantum state of light onto another light beam; later developments used optical relays and demonstrated entanglement swapping for continuous variables. The teleportation of a quantum state between two single material particles (trapped ions) has now also been achieved. Here we demonstrate teleportation between objects of a different nature--light and matter, which respectively represent 'flying' and 'stationary' media. A quantum state encoded in a light pulse is teleported onto a macroscopic object (an atomic ensemble containing 10 caesium atoms). Deterministic teleportation is achieved for sets of coherent states with mean photon number (n) up to a few hundred. The fidelities are 0.58 +/- 0.02 for n = 20 and 0.60 +/- 0.02 for n = 5--higher than any classical state transfer can possibly achieve. Besides being of fundamental interest, teleportation using a macroscopic atomic ensemble is relevant for the practical implementation of a quantum repeater. An important factor for the implementation of quantum networks is the teleportation distance between transmitter and receiver; this is 0.5 metres in the present experiment. As our experiment uses propagating light to achieve the entanglement of light and atoms required for teleportation, the present approach should be scalable to longer distances.
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Affiliation(s)
- Jacob F Sherson
- Niels Bohr Institute, Copenhagen University, Blegdamsvej 17, Copenhagen Ø, Denmark
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20
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Wolf MM, Giedke G, Cirac JI. Extremality of Gaussian quantum states. PHYSICAL REVIEW LETTERS 2006; 96:080502. [PMID: 16606161 DOI: 10.1103/physrevlett.96.080502] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2005] [Indexed: 05/08/2023]
Abstract
We investigate Gaussian quantum states in view of their exceptional role within the space of all continuous variables states. A general method for deriving extremality results is provided and applied to entanglement measures, secret key distillation and the classical capacity of bosonic quantum channels. We prove that for every given covariance matrix the distillable secret key rate and the entanglement, if measured appropriately, are minimized by Gaussian states. This result leads to a clearer picture of the validity of frequently made Gaussian approximations. Moreover, it implies that Gaussian encodings are optimal for the transmission of classical information through bosonic channels, if the capacity is additive.
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Affiliation(s)
- Michael M Wolf
- Max-Planck-Institute for Quantum Optics, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany
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Koike S, Takahashi H, Yonezawa H, Takei N, Braunstein SL, Aoki T, Furusawa A. Demonstration of quantum telecloning of optical coherent states. PHYSICAL REVIEW LETTERS 2006; 96:060504. [PMID: 16605976 DOI: 10.1103/physrevlett.96.060504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2005] [Indexed: 05/08/2023]
Abstract
We demonstrate unconditional telecloning for the first time. In particular, we symmetrically and unconditionally teleclone coherent states of light from one sender to two receivers, achieving a fidelity for each clone of F = 0.58 +/- 0.01, which surpasses the classical limit. This is a manipulation of a new type of multipartite entanglement whose nature is neither purely bipartite nor purely tripartite.
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Affiliation(s)
- Satoshi Koike
- Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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Andersen UL, Sabuncu M, Filip R, Leuchs G. Experimental demonstration of coherent state estimation with minimal disturbance. PHYSICAL REVIEW LETTERS 2006; 96:020409. [PMID: 16486552 DOI: 10.1103/physrevlett.96.020409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2005] [Indexed: 05/06/2023]
Abstract
We investigate the optimal trade-off between information gained about an unknown coherent state and the state disturbance caused by the measurement process. We propose several optical schemes that can enable this task, and we implement one of them, a scheme that relies on only linear optics and homodyne detection. Experimentally we reach near optimal performance, limited only by detection inefficiencies. In addition, we show that such a scheme can be used to enhance the transmission fidelity of a class of noisy channels.
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Affiliation(s)
- Ulrik L Andersen
- Institut für Optik, Information und Photonik, Max-Planck Forschungsgruppe, Universität Erlangen-Nürnberg, Günther-Scharowsky strasse 1, 91058, Erlangen, Germany
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23
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Zhang J, Xie C, Peng K. Continuous-variable quantum state transfer with partially disembodied transport. PHYSICAL REVIEW LETTERS 2005; 95:170501. [PMID: 16383809 DOI: 10.1103/physrevlett.95.170501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Indexed: 05/05/2023]
Abstract
We propose a new protocol of implementing continuous-variable quantum state transfer using partially disembodied transport. This protocol may improve the fidelity at the expense of the introduction of a semiquantum channel between the parties, in comparison with quantum teleportation using the same strength of entanglement. Depending on the amount of information destroyed in the measurement, this protocol may be regarded as a teleportation protocol (complete destruction of input state), or as a cloning protocol (partial destruction), or as a direct transmission (no destruction). This scheme can be straightforwardly implemented with a setup that is at present experimentally accessible.
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Affiliation(s)
- Jing Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, Peoples Republic of China.
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Adesso G, Illuminati F. Equivalence between entanglement and the optimal fidelity of continuous variable teleportation. PHYSICAL REVIEW LETTERS 2005; 95:150503. [PMID: 16241708 DOI: 10.1103/physrevlett.95.150503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Indexed: 05/05/2023]
Abstract
We devise the optimal form of Gaussian resource states enabling continuous-variable teleportation with maximal fidelity. We show that a nonclassical optimal fidelity of N-user teleportation networks is necessary and sufficient for N-party entangled Gaussian resources, yielding an estimator of multipartite entanglement. The entanglement of teleportation is equivalent to the entanglement of formation in a two-user protocol, and to the localizable entanglement in a multiuser one. Finally, we show that the continuous-variable tangle, quantifying entanglement sharing in three-mode Gaussian states, is defined operationally in terms of the optimal fidelity of a tripartite teleportation network.
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Affiliation(s)
- Gerardo Adesso
- Dipartimento di Fisica E. R. Caianiello, Università di Salerno, CNR-Coherentia, Gruppo di Salerno, INFN Sezione di Napoli, Gruppo Collegato di Salerno, Via S. Allende, 84081 Baronissi (SA), Italy
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Cerf NJ, Krüger O, Navez P, Werner RF, Wolf MM. Non-Gaussian cloning of quantum coherent states is optimal. PHYSICAL REVIEW LETTERS 2005; 95:070501. [PMID: 16196769 DOI: 10.1103/physrevlett.95.070501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2004] [Revised: 12/14/2004] [Indexed: 05/04/2023]
Abstract
We consider the optimal cloning of quantum coherent states with single-clone and joint fidelity as figures of merit. While the latter is maximized by a Gaussian cloner, the former is not: the optimal single-clone fidelity for a symmetric 1-to-2 cloner is 0.6826, compared to 2/3 in a Gaussian setting. This cloner can be realized with an optical parametric amplifier and certain non-Gaussian bimodal states. Finally, we show that the single-clone fidelity of the optimal 1-to-infinity cloner is 1/2. It is achieved by a Gaussian scheme and cannot be surpassed even with supplemental bound entangled states.
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Affiliation(s)
- N J Cerf
- QUIC, Ecole Polytechnique, CP 165, Université Libre de Bruxelles, Belgium
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Julsgaard B, Sherson J, Cirac JI, Fiurásek J, Polzik ES. Experimental demonstration of quantum memory for light. Nature 2004; 432:482-6. [PMID: 15565148 DOI: 10.1038/nature03064] [Citation(s) in RCA: 656] [Impact Index Per Article: 32.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Accepted: 09/28/2004] [Indexed: 11/08/2022]
Abstract
The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot be perfectly recorded in a classical memory, even in principle. In the field of quantum information, this has led to the long-standing challenge of how to achieve a high-fidelity transfer of an independently prepared quantum state of light onto an atomic quantum state. Here we propose and experimentally demonstrate a protocol for such a quantum memory based on atomic ensembles. Recording of an externally provided quantum state of light onto the atomic quantum memory is achieved with 70 per cent fidelity, significantly higher than the limit for classical recording. Quantum storage of light is achieved in three steps: first, interaction of the input pulse and an entangling field with spin-polarized caesium atoms; second, subsequent measurement of the transmitted light; and third, feedback onto the atoms using a radio-frequency magnetic pulse conditioned on the measurement result. The density of recorded states is 33 per cent higher than the best classical recording of light onto atoms, with a quantum memory lifetime of up to 4 milliseconds.
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Affiliation(s)
- Brian Julsgaard
- Niels Bohr Institute, Danish Quantum Optics Center-QUANTOP, Copenhagen University, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
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