151
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Renormalization and small-world model of fractal quantum repeater networks. Sci Rep 2013; 3:1222. [PMID: 23386977 PMCID: PMC3564040 DOI: 10.1038/srep01222] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 01/15/2013] [Indexed: 11/25/2022] Open
Abstract
Quantum networks provide access to exchange of quantum information. The primary task of quantum networks is to distribute entanglement between remote nodes. Although quantum repeater protocol enables long distance entanglement distribution, it has been restricted to one-dimensional linear network. Here we develop a general framework that allows application of quantum repeater protocol to arbitrary quantum repeater networks with fractal structure. Entanglement distribution across such networks is mapped to renormalization. Furthermore, we demonstrate that logarithmical times of recursive such renormalization transformations can trigger fractal to small-world transition, where a scalable quantum small-world network is achieved. Our result provides new insight into quantum repeater theory towards realistic construction of large-scale quantum networks.
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152
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Avella A, Gramegna M, Genovese M. Entanglement and Quantum non-locality: an experimental perspective. EPJ WEB OF CONFERENCES 2013. [DOI: 10.1051/epjconf/20135801014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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153
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Quantum teleportation over 143 kilometres using active feed-forward. Nature 2012; 489:269-73. [PMID: 22951967 DOI: 10.1038/nature11472] [Citation(s) in RCA: 113] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Accepted: 08/14/2012] [Indexed: 11/08/2022]
Abstract
The quantum internet is predicted to be the next-generation information processing platform, promising secure communication and an exponential speed-up in distributed computation. The distribution of single qubits over large distances via quantum teleportation is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits, an internal qubit and squeezed states, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation.
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154
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Fel'dman EB, Pyrkov AN, Zenchuk AI. Solid-state multiple quantum NMR in quantum information processing: exactly solvable models. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2012; 370:4690-4712. [PMID: 22946036 DOI: 10.1098/rsta.2011.0499] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Multiple quantum (MQ) NMR is an effective tool for the generation of a large cluster of correlated particles, which, in turn, represent a basis for quantum information processing devices. Studying the available exactly solvable models clarifies many aspects of the quantum information. In this study, we consider two exactly solvable models in the MQ NMR experiment: (i) the isolated system of two spin-1/2 particles (dimers) and (ii) the large system of equivalent spin-1/2 particles in a nanopore. The former model is used to describe the quantum correlations and their relations with the MQ NMR coherences, whereas the latter helps one to model the creation and decay of large clusters of correlated particles.
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Affiliation(s)
- E B Fel'dman
- Institute of Problems of Chemical Physics, RAS, Chernogolovka, Moscow Region 142432, Russia
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155
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Branciard C, Brunner N, Buhrman H, Cleve R, Gisin N, Portmann S, Rosset D, Szegedy M. Classical simulation of entanglement swapping with bounded communication. PHYSICAL REVIEW LETTERS 2012; 109:100401. [PMID: 23005265 DOI: 10.1103/physrevlett.109.100401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Indexed: 06/01/2023]
Abstract
Entanglement appears under two different forms in quantum theory, namely, as a property of states of joint systems and as a property of measurement eigenstates in joint measurements. By combining these two aspects of entanglement, it is possible to generate nonlocality between particles that never interacted, using the protocol of entanglement swapping. We show that even in the more constraining bilocal scenario where distant sources of particles are assumed to be independent, i.e., to share no prior randomness, entanglement swapping can be simulated classically with bounded communication, using only 9 bits in total. Our result thus provides an upper bound on the nonlocality of the entanglement swapping process.
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Affiliation(s)
- Cyril Branciard
- School of Mathematics and Physics, The University of Queensland, St Lucia, QLD 4072, Australia
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156
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Chuan TK, Maillard J, Modi K, Paterek T, Paternostro M, Piani M. Quantum discord bounds the amount of distributed entanglement. PHYSICAL REVIEW LETTERS 2012; 109:070501. [PMID: 23006347 DOI: 10.1103/physrevlett.109.070501] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2012] [Indexed: 06/01/2023]
Abstract
The ability to distribute quantum entanglement is a prerequisite for many fundamental tests of quantum theory and numerous quantum information protocols. Two distant parties can increase the amount of entanglement between them by means of quantum communication encoded in a carrier that is sent from one party to the other. Intriguingly, entanglement can be increased even when the exchanged carrier is not entangled with the parties. However, in light of the defining property of entanglement stating that it cannot increase under classical communication, the carrier must be quantum. Here we show that, in general, the increase of relative entropy of entanglement between two remote parties is bounded by the amount of nonclassical correlations of the carrier with the parties as quantified by the relative entropy of discord. We study implications of this bound, provide new examples of entanglement distribution via unentangled states, and put further limits on this phenomenon.
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Affiliation(s)
- T K Chuan
- Centre for Quantum Technologies, National University of Singapore, Singapore
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157
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Gottesman D, Jennewein T, Croke S. Longer-baseline telescopes using quantum repeaters. PHYSICAL REVIEW LETTERS 2012; 109:070503. [PMID: 23006349 DOI: 10.1103/physrevlett.109.070503] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2011] [Revised: 05/22/2012] [Indexed: 06/01/2023]
Abstract
We present an approach to building interferometric telescopes using ideas of quantum information. Current optical interferometers have limited baseline lengths, and thus limited resolution, because of noise and loss of signal due to the transmission of photons between the telescopes. The technology of quantum repeaters has the potential to eliminate this limit, allowing in principle interferometers with arbitrarily long baselines.
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Affiliation(s)
- Daniel Gottesman
- Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada.
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158
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Hofmann J, Krug M, Ortegel N, Gérard L, Weber M, Rosenfeld W, Weinfurter H. Heralded entanglement between widely separated atoms. Science 2012; 337:72-5. [PMID: 22767924 DOI: 10.1126/science.1221856] [Citation(s) in RCA: 293] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Entanglement is the essential feature of quantum mechanics. Notably, observers of two or more entangled particles will find correlations in their measurement results that cannot be explained by classical statistics. To make it a useful resource, particularly for scalable long-distance quantum communication, the heralded generation of entanglement between distant massive quantum systems is necessary. We report on the creation and analysis of heralded entanglement between spins of two single rubidium-87 atoms trapped independently 20 meters apart. Our results illustrate the viability of an integral resource for quantum information science, as well as for fundamental tests of quantum mechanics.
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Affiliation(s)
- Julian Hofmann
- Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany
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159
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Kalashnikov DA, Tan SH, Krivitsky LA. Crosstalk calibration of multi-pixel photon counters using coherent states. OPTICS EXPRESS 2012; 20:5044-5051. [PMID: 22418309 DOI: 10.1364/oe.20.005044] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We present a novel method of calibration of crosstalk probability for multi-pixel photon counters (MPPCs) based on the measurement of the normalized second-order intensity correlation function of coherent light. The method was tested for several MPPCs, and was shown to be advantageous over the traditional calibration method based on the measurements of the dark noise statistics. The method can be applied without the need of modification for different kinds of spatially resolved single photon detectors.
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Affiliation(s)
- Dmitry A Kalashnikov
- Data Storage Institute, Agency for Science Technology and Research, 5 Engineering Drive I, 117608 Singapore
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160
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Practical photon number detection with electric field-modulated silicon avalanche photodiodes. Nat Commun 2012; 3:644. [DOI: 10.1038/ncomms1641] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 12/14/2011] [Indexed: 11/08/2022] Open
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161
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Ganguly N, Adhikari S, Majumdar AS, Chatterjee J. Entanglement witness operator for quantum teleportation. PHYSICAL REVIEW LETTERS 2011; 107:270501. [PMID: 22243295 DOI: 10.1103/physrevlett.107.270501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2011] [Indexed: 05/31/2023]
Abstract
The ability of entangled states to act as a resource for teleportation is linked to a property of the fully entangled fraction. We show that the set of states with their fully entangled fraction bounded by a threshold value required for performing teleportation is both convex and compact. This feature enables the existence of Hermitian witness operators, the measurement of which could distinguish unknown states useful for performing teleportation. We present an example of such a witness operator illustrating it for different classes of states.
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Affiliation(s)
- Nirman Ganguly
- Department of Mathematics, Heritage Institute of Technology, Kolkata, West Bengal, India.
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162
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Rabelo R, Ho M, Cavalcanti D, Brunner N, Scarani V. Device-independent certification of entangled measurements. PHYSICAL REVIEW LETTERS 2011; 107:050502. [PMID: 21867052 DOI: 10.1103/physrevlett.107.050502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Indexed: 05/31/2023]
Abstract
We present a device-independent protocol to test if a given black-box measurement device is entangled, that is, has entangled eigenstates. Our scheme involves three parties and is inspired by entanglement swapping; the test uses the Clauser-Horne-Shimony-Holt Bell inequality, checked between each pair of parties. In the case where all particles are qubits, we characterize quantitatively the deviation of the measurement device from a perfect Bell-state measurement.
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Affiliation(s)
- Rafael Rabelo
- Centre for Quantum Technologies, National University of Singapore, Singapore
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163
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Wiegner R, Thiel C, von Zanthier J, Agarwal GS. Quantum interference and entanglement of photons that do not overlap in time. OPTICS LETTERS 2011; 36:1512-1514. [PMID: 21499407 DOI: 10.1364/ol.36.001512] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We discuss the possibility of quantum interferences and entanglement of photons that exist at different intervals of time, i.e., one photon being recorded before the other has been created. The corresponding two-photon correlation function is shown to violate Bell's inequalities.
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Affiliation(s)
- R Wiegner
- Institut für Optik, Information und Photonik, Universität Erlangen-Nürnberg, Erlangen, Germany. ‐erlangen.de
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164
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Sangouard N, Sanguinetti B, Curtz N, Gisin N, Thew R, Zbinden H. Faithful entanglement swapping based on sum-frequency generation. PHYSICAL REVIEW LETTERS 2011; 106:120403. [PMID: 21517286 DOI: 10.1103/physrevlett.106.120403] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Indexed: 05/30/2023]
Abstract
We show that an entanglement swapping operation performed with spontaneous parametric down-conversion can be made faithful without postselection using sum-frequency generation. This invites us to revisit the sum-frequency process and from a proof-of-principle experiment, we demonstrate that it provides a realistic solution for nonlinear optics at the single-photon level. This opens the way to attractive alternatives to six-photon protocols based on linear optics used, e.g., for the heralded creation of maximally entangled pairs or for device-independent quantum key distribution.
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Affiliation(s)
- Nicolas Sangouard
- Group of Applied Physics, University of Geneva, 1211 Geneva 4, Switzerland
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165
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An error-free protocol for quantum entanglement distribution in long-distance quantum communication. CHINESE SCIENCE BULLETIN-CHINESE 2011. [DOI: 10.1007/s11434-010-4336-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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166
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Scherer A, Sanders BC, Tittel W. Long-distance practical quantum key distribution by entanglement swapping. OPTICS EXPRESS 2011; 19:3004-3018. [PMID: 21369125 DOI: 10.1364/oe.19.003004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We develop a model for practical, entanglement-based long-distance quantum key distribution employing entanglement swapping as a key building block. Relying only on existing off-the-shelf technology, we show how to optimize resources so as to maximize secret key distribution rates. The tools comprise lossy transmission links, such as telecom optical fibers or free space, parametric down-conversion sources of entangled photon pairs, and threshold detectors that are inefficient and have dark counts. Our analysis provides the optimal trade-off between detector efficiency and dark counts, which are usually competing, as well as the optimal source brightness that maximizes the secret key rate for specified distances (i.e. loss) between sender and receiver.
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Affiliation(s)
- Artur Scherer
- Institute for Quantum Information Science, University of Calgary, Calgary, AB, Canada T2N 1N4.
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167
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Coello JG, Bayat A, Bose S, Jefferson JH, Creffield CE. Spin filtering and entanglement swapping through coherent evolution of a single quantum dot. PHYSICAL REVIEW LETTERS 2010; 105:080502. [PMID: 20868084 DOI: 10.1103/physrevlett.105.080502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 06/12/2010] [Indexed: 05/29/2023]
Abstract
We exploit the nondissipative dynamics of a pair of electrons in a large square quantum dot to perform singlet-triplet spin measurement through a single charge detection and show how this may be used for entanglement swapping and teleportation. The method is also used to generate the Affleck-Kennedy-Lieb-Tasaki ground state, a further resource for quantum computation. We justify, and derive analytic results for, an effective charge-spin Hamiltonian which is valid over a wide range of parameters and agrees well with exact numerical results of a realistic effective-mass model. Our analysis also indicates that the method is robust to the choice of dot-size and initialization errors, as well as decoherence.
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Affiliation(s)
- Jose Garcia Coello
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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168
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169
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Fowler AG, Wang DS, Hill CD, Ladd TD, Van Meter R, Hollenberg LCL. Surface code quantum communication. PHYSICAL REVIEW LETTERS 2010; 104:180503. [PMID: 20482159 DOI: 10.1103/physrevlett.104.180503] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2010] [Indexed: 05/29/2023]
Abstract
Quantum communication typically involves a linear chain of repeater stations, each capable of reliable local quantum computation and connected to their nearest neighbors by unreliable communication links. The communication rate of existing protocols is low as two-way classical communication is used. By using a surface code across the repeater chain and generating Bell pairs between neighboring stations with probability of heralded success greater than 0.65 and fidelity greater than 0.96, we show that two-way communication can be avoided and quantum information can be sent over arbitrary distances with arbitrarily low error at a rate limited only by the local gate speed. This is achieved by using the unreliable Bell pairs to measure nonlocal stabilizers and feeding heralded failure information into post-transmission error correction. Our scheme also applies when the probability of heralded success is arbitrarily low.
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Affiliation(s)
- Austin G Fowler
- Centre for Quantum Computer Technology, School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
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170
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Branciard C, Gisin N, Pironio S. Characterizing the nonlocal correlations created via entanglement swapping. PHYSICAL REVIEW LETTERS 2010; 104:170401. [PMID: 20482092 DOI: 10.1103/physrevlett.104.170401] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2009] [Indexed: 05/29/2023]
Abstract
Quantum systems that have never interacted can become nonlocally correlated through a process called entanglement swapping. To characterize nonlocality in this context, we introduce local models where quantum systems that are initially uncorrelated are described by uncorrelated local variables. This additional assumption leads to stronger tests of nonlocality. We show, in particular, that an entangled pair generated through entanglement swapping will already violate a Bell-type inequality for visibilities as low as 50% under our assumption.
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Affiliation(s)
- C Branciard
- Group of Applied Physics, University of Geneva, 20 rue de l'Ecole-de-Médecine, CH-1211 Geneva 4, Switzerland
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171
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Abstract
A photon echo storage-time extension protocol is presented by using a phase locking method in a three-level backward propagation scheme, where phase locking serves as a conditional stopper of the rephasing process in conventional two-pulse photon echoes. The backward propagation scheme solves the critical problems of extremely low retrieval efficiency and pi rephasing pulse-caused spontaneous emission noise in photon echo based quantum memories. The physics of the storage time extension lies in the imminent population transfer from the excited state to an auxiliary spin state by a phase locking control pulse. We numerically demonstrate that the storage time is lengthened by spin dephasing time.
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Affiliation(s)
- Byoung S Ham
- Center for Photon Information Processing, Department of Electrical Engineering, and Graduate School of Information and Telecommunications, Inha University, Incheon, South Korea.
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172
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Isenhower L, Urban E, Zhang XL, Gill AT, Henage T, Johnson TA, Walker TG, Saffman M. Demonstration of a neutral atom controlled-NOT quantum gate. PHYSICAL REVIEW LETTERS 2010; 104:010503. [PMID: 20366355 DOI: 10.1103/physrevlett.104.010503] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Indexed: 05/29/2023]
Abstract
We present the first demonstration of a CNOT gate between two individually addressed neutral atoms. Our implementation of the CNOT uses Rydberg blockade interactions between neutral atoms held in optical traps separated by >8 microm. Using two different gate protocols we measure CNOT fidelities of F=0.73 and 0.72 based on truth table probabilities. The gate was used to generate Bell states with fidelity F=0.48+/-0.06. After correcting for atom loss we obtain an a posteriori entanglement fidelity of F=0.58.
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Affiliation(s)
- L Isenhower
- Department of Physics, University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706 USA
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173
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174
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Cho SB, Noh TG. Stabilization of a long-armed fiber-optic single-photon interferometer. OPTICS EXPRESS 2009; 17:19027-19032. [PMID: 20372637 DOI: 10.1364/oe.17.019027] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We report on single-photon interference experiments in a Michelson-type interferometer built with two 6-km-long fiber spools, as well as on the active stabilization of the interferometer. A weak coherent light signal was (de-) multiplexed with a strong reference light using wavelength-division multiplexing technique, and real-time feedback control technique was applied for the reference light to actively stabilize the phase fluctuation in the long-armed fiber interferometer. The stabilized interferometer showed phase stability of 0.06 rad, which corresponds to an optical path length fluctuation of 15 nm between the 6-km-long interfering arms. The raw visibility obtained without subtracting noise counts in the single-photon interference experiment was more than 98% for stabilized conditions.
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Affiliation(s)
- Seok-Beom Cho
- Electronics and Telecommunications Research Institute, Daejeon 305-700, Korea
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175
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Pawłowski M, Paterek T, Kaszlikowski D, Scarani V, Winter A, Żukowski M. Information causality as a physical principle. Nature 2009; 461:1101-4. [DOI: 10.1038/nature08400] [Citation(s) in RCA: 475] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Accepted: 08/13/2009] [Indexed: 11/09/2022]
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176
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Lu CY, Yang T, Pan JW. Experimental multiparticle entanglement swapping for quantum networking. PHYSICAL REVIEW LETTERS 2009; 103:020501. [PMID: 19659188 DOI: 10.1103/physrevlett.103.020501] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Indexed: 05/28/2023]
Abstract
This Letter reports the first experimental demonstration of Greenberger-Horne-Zeilinger (GHZ) entanglement swapping. We start with three pairs of entangled photons. Upon projection of three single photons, each from an entangled pair, into a GHZ state, the other three originally independent photons are entangled in a GHZ state-creation of multiparticle entanglement without any direct interaction. This scheme may facilitate networks for quantum telephone exchange, multiparty quantum communication and distributed quantum computation.
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Affiliation(s)
- Chao-Yang Lu
- Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
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177
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Lee JS, Khitrin AK. Projection of a quantum state on eigenstates of average Hamiltonian. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2009; 198:248-51. [PMID: 19303799 DOI: 10.1016/j.jmr.2009.02.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2008] [Revised: 02/14/2009] [Accepted: 02/27/2009] [Indexed: 05/24/2023]
Abstract
A scheme for projecting an arbitrary quantum state on eigenstates of average Hamiltonian is described. As an experimental example, projection on entangled Bell states, which are eigenstates of specially constructed average Hamiltonian, is demonstrated for a system of two dipolar-coupled nuclear spins. The results of a direct and time-reversed evolution are added to average out the coherences between different eigenstates and accomplish the projection.
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Affiliation(s)
- Jae-Seung Lee
- Department of Chemistry, Kent State University, Kent, OH 44242-0001, USA.
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178
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Skrzypczyk P, Brunner N, Popescu S. Emergence of quantum correlations from nonlocality swapping. PHYSICAL REVIEW LETTERS 2009; 102:110402. [PMID: 19392175 DOI: 10.1103/physrevlett.102.110402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Indexed: 05/27/2023]
Abstract
By studying generalized nonsignaling theories, the hope is to find out what makes quantum mechanics so special. In the present Letter, we revisit the paradigmatic model of nonsignaling boxes and introduce the concept of a genuine box. This will allow us to present the first generalized nonsignaling model featuring quantumlike dynamics. In particular, we present the coupler, a device enabling nonlocality swapping, the analogue of quantum entanglement swapping, as well as teleportation. Remarkably, part of the boundary between quantum and post-quantum correlations emerges in our study.
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Affiliation(s)
- Paul Skrzypczyk
- H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom.
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179
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Rosenfeld W, Hocke F, Henkel F, Krug M, Volz J, Weber M, Weinfurter H. Towards long-distance atom-photon entanglement. PHYSICAL REVIEW LETTERS 2008; 101:260403. [PMID: 19437626 DOI: 10.1103/physrevlett.101.260403] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report the observation of entanglement between a single trapped atom and a single photon at remote locations. The degree of coherence of the entangled atom-photon pair is verified via appropriate local correlation measurements, after communicating the photon via an optical fiber link of 300 m length to a receiver 3.5 m apart. In addition, we measured the temporal evolution of the atomic density matrix after projecting the atom via a state measurement of the photon onto several well-defined spin states. We find that the state of the single atom dephases on a time scale of 150 micros, which represents an important step towards long-distance quantum networking with individual neutral atoms.
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Affiliation(s)
- W Rosenfeld
- Fakultät für Physik, Ludwig-Maximilians-Universität München, D-80799 München, Germany
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180
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Yuan ZS, Chen YA, Zhao B, Chen S, Schmiedmayer J, Pan JW. Experimental demonstration of a BDCZ quantum repeater node. Nature 2008; 454:1098-101. [PMID: 18756253 DOI: 10.1038/nature07241] [Citation(s) in RCA: 331] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2008] [Accepted: 07/03/2008] [Indexed: 11/09/2022]
Abstract
Quantum communication is a method that offers efficient and secure ways for the exchange of information in a network. Large-scale quantum communication (of the order of 100 km) has been achieved; however, serious problems occur beyond this distance scale, mainly due to inevitable photon loss in the transmission channel. Quantum communication eventually fails when the probability of a dark count in the photon detectors becomes comparable to the probability that a photon is correctly detected. To overcome this problem, Briegel, Dür, Cirac and Zoller (BDCZ) introduced the concept of quantum repeaters, combining entanglement swapping and quantum memory to efficiently extend the achievable distances. Although entanglement swapping has been experimentally demonstrated, the implementation of BDCZ quantum repeaters has proved challenging owing to the difficulty of integrating a quantum memory. Here we realize entanglement swapping with storage and retrieval of light, a building block of the BDCZ quantum repeater. We follow a scheme that incorporates the strategy of BDCZ with atomic quantum memories. Two atomic ensembles, each originally entangled with a single emitted photon, are projected into an entangled state by performing a joint Bell state measurement on the two single photons after they have passed through a 300-m fibre-based communication channel. The entanglement is stored in the atomic ensembles and later verified by converting the atomic excitations into photons. Our method is intrinsically phase insensitive and establishes the essential element needed to realize quantum repeaters with stationary atomic qubits as quantum memories and flying photonic qubits as quantum messengers.
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Affiliation(s)
- Zhen-Sheng Yuan
- Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany
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181
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Chuu CS, Strassel T, Zhao B, Koch M, Chen YA, Chen S, Yuan ZS, Schmiedmayer J, Pan JW. Quantum memory with optically trapped atoms. PHYSICAL REVIEW LETTERS 2008; 101:120501. [PMID: 18851349 DOI: 10.1103/physrevlett.101.120501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Indexed: 05/26/2023]
Abstract
We report the experimental demonstration of quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Nonclassical correlations are observed for storage times up to 60 mus.
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Affiliation(s)
- Chih-Sung Chuu
- Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany.
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182
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Goebel AM, Wagenknecht C, Zhang Q, Chen YA, Chen K, Schmiedmayer J, Pan JW. Multistage entanglement swapping. PHYSICAL REVIEW LETTERS 2008; 101:080403. [PMID: 18764594 DOI: 10.1103/physrevlett.101.080403] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Indexed: 05/26/2023]
Abstract
We report an experimental demonstration of entanglement swapping over two quantum stages. By successful realizations of two cascaded photonic entanglement swapping processes, entanglement is generated and distributed between two photons, that originate from independent sources and do not share any common past. In the experiment we use three pairs of polarization entangled photons and conduct two Bell-state measurements: one between the first and second pair, and one between the second and third pair. This results in projecting the remaining two outgoing photons from pair 1 and 3 into an entangled state, as characterized by an entanglement witness. The experiment represents an important step towards a full quantum repeater where multiple entanglement swapping is a key ingredient.
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Affiliation(s)
- Alexander M Goebel
- Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany
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183
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Zipper E, Kurpas M, Dajka J, Kuś M. Entanglement of distant flux qubits mediated by non-classical electromagnetic field. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:275219. [PMID: 21694380 DOI: 10.1088/0953-8984/20/27/275219] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The mechanism for entanglement of two flux qubits each interacting with a single mode electromagnetic field is discussed. By performing a Bell state measurement (BSM) on photons we find the two qubits in an entangled state depending on the system parameters. We discuss the results for two initial states and take into consideration the influence of decoherence.
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Affiliation(s)
- E Zipper
- Institute of Physics, University of Silesia, Ulica Uniwersytecka 4, 40-007 Katowice, Poland
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184
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Matsukevich DN, Maunz P, Moehring DL, Olmschenk S, Monroe C. Bell inequality violation with two remote atomic qubits. PHYSICAL REVIEW LETTERS 2008; 100:150404. [PMID: 18518088 DOI: 10.1103/physrevlett.100.150404] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2008] [Indexed: 05/26/2023]
Abstract
We observe violation of a Bell inequality between the quantum states of two remote Yb+ ions separated by a distance of about 1 m with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography.
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Affiliation(s)
- D N Matsukevich
- Department of Physics and Joint Quantum Institute, University of Maryland, College Park, MD 20742, USA.
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185
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Optimal approach to quantum communication using dynamic programming. Proc Natl Acad Sci U S A 2007; 104:17291-6. [PMID: 17959783 DOI: 10.1073/pnas.0703284104] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Reliable preparation of entanglement between distant systems is an outstanding problem in quantum information science and quantum communication. In practice, this has to be accomplished by noisy channels (such as optical fibers) that generally result in exponential attenuation of quantum signals at large distances. A special class of quantum error correction protocols, quantum repeater protocols, can be used to overcome such losses. In this work, we introduce a method for systematically optimizing existing protocols and developing more efficient protocols. Our approach makes use of a dynamic programming-based searching algorithm, the complexity of which scales only polynomially with the communication distance, letting us efficiently determine near-optimal solutions. We find significant improvements in both the speed and the final-state fidelity for preparing long-distance entangled states.
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186
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Rosenfeld W, Berner S, Volz J, Weber M, Weinfurter H. Remote preparation of an atomic quantum memory. PHYSICAL REVIEW LETTERS 2007; 98:050504. [PMID: 17358837 DOI: 10.1103/physrevlett.98.050504] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Indexed: 05/14/2023]
Abstract
Storage and distribution of quantum information are key elements of quantum information processing and future quantum communication networks. Here, using atom-photon entanglement as the main physical resource, we experimentally demonstrate the preparation of a distant atomic quantum memory. Applying a quantum teleportation protocol on a locally prepared state of a photonic qubit, we realized this so-called remote state preparation on a single, optically trapped 87Rb atom. We evaluated the performance of this scheme by the full tomography of the prepared atomic state, reaching an average fidelity of 82%.
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Affiliation(s)
- Wenjamin Rosenfeld
- Department für Physik, Ludwig-Maximilians Universität München, D-80799 München, Germany.
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187
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ZUKOWSKI MAREK, ZEILINGER ANTON, WEINFURTER HARALD. Entangling Photons Radiated by Independent Pulsed Sourcesa. Ann N Y Acad Sci 2006. [DOI: 10.1111/j.1749-6632.1995.tb38959.x] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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188
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de Visser RL, Blaauboer M. Deterministic teleportation of electrons in a quantum dot nanostructure. PHYSICAL REVIEW LETTERS 2006; 96:246801. [PMID: 16907265 DOI: 10.1103/physrevlett.96.246801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Indexed: 05/11/2023]
Abstract
We present a proposal for deterministic quantum teleportation of electrons in a semiconductor nanostructure consisting of a single and a double quantum dot. The central issue addressed in this Letter is how to design and implement the most efficient--in terms of the required number of single and two-qubit operations--deterministic teleportation protocol for this system. Using a group-theoretical analysis, we show that deterministic teleportation requires a minimum of three single-qubit rotations and two entangling (square root SWAP) operations. These can be implemented for spin qubits in quantum dots using electron-spin resonance (for single-spin rotations) and exchange interaction (for square root SWAP operations).
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Affiliation(s)
- R L de Visser
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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189
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Chen YA, Zhang AN, Zhao Z, Zhou XQ, Pan JW. Experimental quantum error rejection for quantum communication. PHYSICAL REVIEW LETTERS 2006; 96:220504. [PMID: 16803294 DOI: 10.1103/physrevlett.96.220504] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Indexed: 05/10/2023]
Abstract
We report an experimental demonstration of a bit-flip error-rejection protocol for error-reduced transfer of quantum information through a noisy quantum channel. In the experiment, an unknown state to be transmitted is encoded into a two-photon entangled state, which is then sent through an engineered noisy quantum channel. At the final stage, the unknown state is decoded by a parity measurement, successfully rejecting the erroneous transmission over the noisy quantum channel.
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Affiliation(s)
- Yu-Ao Chen
- Physikalisches Institut, Universität Heidelberg, Philosophenweg 12, D-69120 Heidelberg, Germany
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190
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Yang T, Zhang Q, Chen TY, Lu S, Yin J, Pan JW, Wei ZY, Tian JR, Zhang J. Experimental synchronization of independent entangled photon sources. PHYSICAL REVIEW LETTERS 2006; 96:110501. [PMID: 16605806 DOI: 10.1103/physrevlett.96.110501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Indexed: 05/08/2023]
Abstract
We report the generation of independent entangled photon pairs from two synchronized but mutually incoherent laser sources. The quality of synchronization is confirmed by observing a violation of Bell's inequality with 3.2 standard deviations in an entanglement swapping experiment. The techniques developed in our experiment are not only important for realistic linear optical quantum-information processing, but also enable new tests of local realism.
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Affiliation(s)
- Tao Yang
- Department of Modern Physics and Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
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191
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Childress L, Taylor JM, Sørensen AS, Lukin MD. Fault-tolerant quantum communication based on solid-state photon emitters. PHYSICAL REVIEW LETTERS 2006; 96:070504. [PMID: 16606069 DOI: 10.1103/physrevlett.96.070504] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2004] [Revised: 11/11/2005] [Indexed: 05/08/2023]
Abstract
We describe a novel protocol for a quantum repeater that enables long-distance quantum communication through realistic, lossy photonic channels. Contrary to previous proposals, our protocol incorporates active purification of arbitrary errors at each step of the protocol using only two qubits at each repeater station. Because of these minimal physical requirements, the present protocol can be realized in simple physical systems such as solid-state single photon emitters. As an example, we show how nitrogen-vacancy color centers in diamond can be used to implement the protocol, using the nuclear and electronic spin to form the two qubits.
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Affiliation(s)
- L Childress
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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192
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Volz J, Weber M, Schlenk D, Rosenfeld W, Vrana J, Saucke K, Kurtsiefer C, Weinfurter H. Observation of entanglement of a single photon with a trapped atom. PHYSICAL REVIEW LETTERS 2006; 96:030404. [PMID: 16486671 DOI: 10.1103/physrevlett.96.030404] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2005] [Indexed: 05/06/2023]
Abstract
We report the observation of entanglement between a single trapped atom and a single photon at a wavelength suitable for low-loss communication over large distances, thereby achieving a crucial step towards long range quantum networks. To verify the entanglement, we introduce a single atom state analysis. This technique is used for full state tomography of the atom-photon qubit pair. The detection efficiency and the entanglement fidelity are high enough to allow in a next step the generation of entangled atoms at large distances, ready for a final loophole-free Bell experiment.
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Affiliation(s)
- Jürgen Volz
- Department für Physik, Ludwig-Maximilians-Universität München, D-80799 München, Germany.
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193
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Rarity JG, Tapster PR, Loudon R. Non-classical interference between independent sources. ACTA ACUST UNITED AC 2005. [DOI: 10.1088/1464-4266/7/7/007] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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194
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Peng CZ, Yang T, Bao XH, Zhang J, Jin XM, Feng FY, Yang B, Yang J, Yin J, Zhang Q, Li N, Tian BL, Pan JW. Experimental free-space distribution of entangled photon pairs over 13 km: towards satellite-based global quantum communication. PHYSICAL REVIEW LETTERS 2005; 94:150501. [PMID: 15904125 DOI: 10.1103/physrevlett.94.150501] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2004] [Indexed: 05/02/2023]
Abstract
We report free-space distribution of entangled photon pairs over a noisy ground atmosphere of 13 km. It is shown that the desired entanglement can still survive after both entangled photons have passed through the noisy ground atmosphere with a distance beyond the effective thickness of the aerosphere. This is confirmed by observing a spacelike separated violation of Bell inequality of 2.45+/-0.09. On this basis, we exploit the distributed entangled photon source to demonstrate the Bennett-Brassard 1984 quantum cryptography scheme. The distribution distance of entangled photon pairs achieved in the experiment is for the first time well beyond the effective thickness of the aerosphere, hence presenting a significant step towards satellite-based global quantum communication.
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Affiliation(s)
- Cheng-Zhi Peng
- Department of Modern Physics and Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China
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195
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Abstract
One hundred years ago Albert Einstein introduced the concept of the photon. Although in the early years after 1905 the evidence for the quantum nature of light was not compelling, modern experiments--especially those using photon pairs--have beautifully confirmed its corpuscular character. Research on the quantum properties of light (quantum optics) triggered the evolution of the whole field of quantum information processing, which now promises new technology, such as quantum cryptography and even quantum computers.
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Affiliation(s)
- Anton Zeilinger
- Institute for Experimental Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
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196
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Gour G, Sanders BC. Remote preparation and distribution of bipartite entangled states. PHYSICAL REVIEW LETTERS 2004; 93:260501. [PMID: 15697959 DOI: 10.1103/physrevlett.93.260501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2004] [Indexed: 05/24/2023]
Abstract
We prove a powerful theorem for tripartite remote entanglement distribution protocols that establishes an upper bound on the amount of entanglement of formation that can be created between two single-qubit nodes of a quantum network. Our theorem also provides an operational interpretation of concurrence as a type of entanglement capacity.
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Affiliation(s)
- Gilad Gour
- Theoretical Physics Institute, University of Alberta, Edmonton, Alberta T6G 2J1, Canada.
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197
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Verstraete F, Martín-Delgado MA, Cirac JI. Diverging entanglement length in gapped quantum spin systems. PHYSICAL REVIEW LETTERS 2004; 92:087201. [PMID: 14995807 DOI: 10.1103/physrevlett.92.087201] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2003] [Indexed: 05/24/2023]
Abstract
We prove the existence of gapped quantum Hamiltonians whose ground states exhibit an infinite entanglement length, as opposed to their finite correlation length. Using the concept of entanglement swapping, the localizable entanglement is calculated exactly for valence bond and finitely correlated states, and the existence of the so-called string-order parameter is discussed. We also report on evidence that the ground state of an antiferromagnetic chain can be used as a perfect quantum channel if local measurements on the individual spins can be implemented.
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Affiliation(s)
- F Verstraete
- Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany
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198
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Beenakker CWJ, Kindermann M. Quantum teleportation by particle-hole annihilation in the Fermi sea. PHYSICAL REVIEW LETTERS 2004; 92:056801. [PMID: 14995326 DOI: 10.1103/physrevlett.92.056801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Indexed: 05/24/2023]
Abstract
We point out that the mutual annihilation of an electron-hole pair at a tunnel barrier leads to teleportation of the state of the annihilated electron to a second, distant electron--if the latter was previously entangled with the annihilated hole. We propose an experiment, involving low-frequency noise measurements on a two-dimensional electron gas in a high magnetic field, to detect teleportation of electrons and holes in the two lowest Landau levels.
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Affiliation(s)
- C W J Beenakker
- Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands
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199
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Xiang-Bin W. Possibility of producing the event-ready two-photon polarization entangled state with normal photon detectors. PHYSICAL REVIEW A 2003; 68:042304. [DOI: 10.1103/physreva.68.042304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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200
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Pittman TB, Franson JD. Violation of Bell's inequality with photons from independent sources. PHYSICAL REVIEW LETTERS 2003; 90:240401. [PMID: 12857180 DOI: 10.1103/physrevlett.90.240401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2003] [Indexed: 05/24/2023]
Abstract
We report a violation of Bell's inequality using one photon from a parametric down-conversion source and a second photon from an attenuated laser beam. The two photons were entangled at a beam splitter using the postselection technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]]. A quantum interference pattern with a visibility of 91% was obtained using the photons from these independent sources, as compared with a visibility of 99.4% using two photons from a central parametric down-conversion source.
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Affiliation(s)
- T B Pittman
- Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723, USA
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