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Perfect excitation of a matter qubit by a single photon in free space

EPL 2009年第1期86卷

作者： Stobinska, M. Alber, G. Leuchs, G. Max Planck Inst Sci Light D-91058 Erlangen Germany Univ Erlangen Nurnberg Inst Opt Informat & Photon D-91058 Erlangen Germany Tech Univ Darmstadt Inst Angew Phys D-64289 Darmstadt Germany

We propose a scheme for perfect excitation of a single two-level atom by a single photon in free space. The photon state has to match the time reversed photon state originating from spontaneous decay of a two-level system. Here, we discuss its experimental preparation. The state is characterized by a particular asymmetric exponentially shaped temporal profile. Any deviations from this ideal state limit the maximum absorption. Although perfect excitation requires an infinite amount of time, we demonstrate that there is a class of initial one-photon quantum states which can achieve almost perfect absorption even for a finite interaction time. Our results pave the way for realizing perfect coupling between flying and stationary qubits in free space thus opening a possibility for building scalable quantum networks. Copyright (C) EPLA, 2009

关键词： quantum description of interaction of light and matter, related experiments quantum computation architectures and implementations

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Holonomic quantum computation associated with a defect structure of conical graphene

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EPL 2009年第3期87卷

作者： Bakke, K. Furtado, C. Sergeenkov, S. Univ Fed Paraiba Dept Fis BR-58051970 Joao Pessoa Paraiba Brazil

A possibility of holonomic quantum computation based on the defect- mediated properties of graphite cones is discussed. Using a geometric description for the conical graphene, we demonstrate how one can construct the most important one-qubit quantum gates without invoking the adiabatic approximation. The control parameter which defines a particular qubit configuration is directly linked with the number of removed sectors in the graphene layer needed to create a particular conical configuration. Copyright (C) EPLA, 2009

关键词： quantum computation architectures and implementations Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals

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Cavity grid for scalable quantum computation with superconducting circuits

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EPL 2009年第5期85卷

作者： Helmer, F. Mariantoni, M. Fowler, A. G. von Delft, J. Solano, E. Marquardt, F. Univ Munich Dept Phys CENS D-80333 Munich Germany Univ Munich ASC D-80333 Munich Germany Bayer Akad Wissensch Walther Meissner Inst D-85748 Garching Germany Tech Univ Munich Dept Phys D-85748 Garching Germany Univ Waterloo Inst Quantum Comp Waterloo ON N2L 3G1 Canada Univ Basque Country Dept Quim Fis E-48080 Bilbao Spain

We propose an architecture for quantum computing based on superconducting circuits, where on-chip planar microwave resonators are arranged in a two-dimensional grid with a qubit at each intersection. This allows any two qubits on the grid to be coupled at a swapping overhead independent of their distance. We demonstrate that this approach encompasses the fundamental elements of a scalable fault-tolerant quantum-computing architecture. Copyright (C) EPLA, 2009

关键词： quantum computation architectures and implementations Cavity quantum electrodynamics, micromasers Superconducting devices

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Large-scale quantum computation in an anharmonic linear ion trap

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EPL 2009年第6期86卷

作者： Lin, G. -D. Zhu, S. -L. Islam, R. Kim, K. Chang, M. -S. Korenblit, S. Monroe, C. Duan, L. -M. Univ Michigan FOCUS Ctr Ann Arbor MI 48109 USA Univ Michigan MCTP Dept Phys Ann Arbor MI 48109 USA S China Normal Univ LQIT Guangzhou Guangdong Peoples R China S China Normal Univ ICMP Dept Phys Guangzhou Guangdong Peoples R China Univ Maryland Joint Quantum Inst College Pk MD 20742 USA Natl Inst Stand & Technol College Pk MD 20742 USA

We propose a large-scale quantum computer architecture by more easily stabilizing a single large linear ion chain in a very simple trap geometry. By confining ions in an anharmonic linear trap with nearly uniform spacing between ions, we show that high-fidelity quantum gates can be realized in large linear ion crystals under the Doppler temperature based on coupling to a near-continuum of transverse motional modes with simple shaped laser pulses. Copyright (C) EPLA, 2009

关键词： quantum computation architectures and implementations Coherent control of atomic interactions with photons quantum error correction and other methods for protection against decoherence

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Electrons in a cryogenic planar Penning trap and experimental challenges for quantum processing

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EUROPEAN PHYSICAL JOURNAL D 2008年第1期50卷 97-102页

作者： Bushev, P. Stahl, S. Natali, R. Marx, G. Stachowska, E. Werth, G. Hellwig, M. Schmidt-Kaler, F. Univ Ulm D-89069 Ulm Germany Johannes Gutenberg Univ Mainz Inst Phys D-55099 Mainz Germany Ernst Moritz Arndt Univ Greifswald Inst Phys D-17489 Greifswald Germany Univ Camerino Dipartimento Fis I-62032 Camerino Italy Poznan Tech Univ PL-60965 Poznan Poland

We report on trapping of clouds of electrons in a cryogenic planar Penning trap at T <= 100 mK. We describe the experimental conditions to load, cool and detect electrons. Perspectives for the trapping of a single ... 详细信息

关键词： Atom, molecule, and ion cooling methods quantum computation architectures and implementations

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The Peierls distorted chain as a quantum data bus for quantum state transfer

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EPL 2008年第3期84卷

作者： Huo, M. X. Li, Ying Song, Z. Sun, C. P. Nankai Univ Dept Phys Tianjin 300071 Peoples R China Chinese Acad Sci Inst Theoret Phys Beijing 100080 Peoples R China

We study the quantum state transfer (QST) of an electron spin along the half-filled Peierls distorted chain (PDC). As has been proved, this solvable and feasible gapped model can accomplish a high-fidelity and long-distance QST. Moreover, numerical simulations are performed in and near the non-distortion point which is beyond the range of perturbation. The result shows that the efficiency of the QST is sensitive to the uniform-to-distorted transition of the PDC, which is related to the transition between the conductor and the insulator. Then this scheme can also be employed to probe the conductor-to-insulator transition of the PDC. Copyright (C) EPLA, 2008

关键词： Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.) Quantized spin models quantum computation architectures and implementations

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Geometric vs. dynamical gates in quantum computing implementations using Zeeman and Heisenberg Hamiltonians

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EPL 2008年第5期83卷

作者： Shi, Yu Fudan Univ Dept Phys Shanghai 200433 Peoples R China

quantum computing in terms of geometric phases, i.e. Berry or Aharonov-Anandan phases, is fault-tolerant to a certain degree. We examine its implementation based on Zeeman coupling with a rotating field and isotropic Heisenberg interaction, which describe NMR and can also be realized in quantum dots and cold atoms. Using a novel physical representation of the qubit basis states, we construct pi/8 and Hadamard gates based on Berry and Aharonov-Anandan phases. For two interacting qubits in a rotating field, we find that it is always impossible to construct a two-qubit gate based on Berry phases, or based on Aharonov-Anandan phases when the gyromagnetic ratios of the two qubits are equal. In implementing a universal set of quantum gates, one may combine geometric pi/8 and Hadamard gates and dynamical v SWAP gate. Copyright (c) EPLA, 2008.

关键词： quantum computation architectures and implementations Phases: geometric, dynamic or topological quantum dots

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Ultra long spin coherence time for Fe³⁺ in ZnO: A new spin qubit

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EPL 2008年第2期84卷

作者： Tribollet, J. Behrends, J. Lips, K. Hahn Meitner Inst Berlin GmbH Abt Silizium Photovolta D-12489 Berlin Germany

We show by means of two pulse electron spin echo experiments on Fe3+ transition metal ions in natural ZnO that their spins S = 5/2 have a spin coherence time limited at T = 6K first by instantaneous diffusion (approximate to 150 mu s), then by nuclear spectral diffusion (approximate to 450 mu s) and ultimately by spin-lattice processes (approximate to 1.4 ms). We predict a spin coherence time in the millisecond range for such a spin qubit in isotopically and chemically purified ZnO. The spin state of a single Fe3+ spin qubit could be readout by optical methods and it could be coherently manipulated using pulsed electron spin resonance (ESR) methods. A free carrier electrically gated between two nearby Fe3+ ions could efficiently couple two Fe3+ spin qubits. All those elements suggest the high potential of the Fe3+ spin qubits in ZnO for the implementation of a scalable ESR quantum computer. Copyright (C) EPLA, 2008

关键词： quantum computation architectures and implementations Electron paramagnetic resonance and relaxation Iron group (3d) ions and impurities (Ti-Cu)

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NMR implementation of factoring large numbers with Gauss sums: Suppression of ghost factors

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EPL 2008年第4期84卷

作者： Peng, X. Suter, D. Tech Univ Dortmund Fak Phys D-44221 Dortmund Germany

Finding the factors of an integer can be achieved by various experimental techniques, based on an algorithm developed by Schleich et al. (Fortschr. Phys., 54 (2006) 856), which uses specific properties of Gauss sums. Experimental limitations usually require truncation of these series, but if the truncation parameter is too small, it is no longer possible to distinguish between factors and so-called "ghost" factors. Here, we discuss two techniques for distinguishing between true factors and ghost factors while keeping the number of terms in the sum constant or only slowly increasing. We experimentally test these modified algorithms in a nuclear spin system, using NMR. Copyright (C) EPLA, 2008

关键词： quantum computation architectures and implementations Algebraic structures and number theory Nuclear magnetic resonance

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Reproducing spin lattice models in strongly coupled atom-cavity systems

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EPL 2008年第2期84卷

作者： Kay, A. Angelakis, D. G. Univ Cambridge Ctr Math Sci DAMTP Ctr Quantum Computat Cambridge CB3 0WA England Tech Univ Crete Chania Dept Sci Iraklion 73100 Greece Natl Univ Singapore Ctr Quantum Technol Singapore 117543 Singapore

In an array of coupled cavities where the cavities are doped with an atomic V-system, and the two excited levels couple to cavity photons of different polarizations, we show how to construct various spin models employed in characterizing phenomena in condensed matter physics, such as the spin-(1/2) Ising, XX, Heisenberg, and XXZ models. The ability to construct networks of arbitrary geometry also allows for the simulation of topological effects. By tuning the number of excitations present, the dimension of the spin to be simulated can be controlled, and mixtures of different spin types produced. The facility of single-site addressing, the use of only the natural hopping photon dynamics without external fields, and the recent experimental advances towards strong coupling, makes the prospect of using these arrays as efficient quantum simulators promising. Copyright (C) EPLA, 2008

关键词： quantum computation architectures and implementations quantum phase transitions Spin chain models

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