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EPL 2017年第3期118卷 30003-30003页

作者： Hen, I. Univ Southern Calif Informat Sci Inst Marina Del Rey CA 90292 USA Univ Southern Calif Dept Phys & Astron Los Angeles CA 90089 USA Univ Southern Calif Ctr Quantum Informat Sci & Technol Los Angeles CA 90089 USA

Grover's unstructured search algorithm is one of the best examples to date for the superiority of quantum algorithms over classical ones. Its applicability, however, has been questioned by many due to its oracular nature. We propose a mechanism to carry out a quantum adiabatic variant of Grover's search algorithm using a single bosonic particle placed in an optical lattice. By studying the scaling of the gap and relevant matrix element in various spatial dimensions, we show that a quantum speedup can already be gained in three dimensions. We argue that the suggested scheme is realizable with present-day experimental capabilities.

关键词： quantum algorithms, protocols, and simulations quantum computation architectures and implementations Atoms in optical lattices

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Implementing a neutral-atom controlled-phase gate with a single Rydberg pulse

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EPL 2016年第4期113卷 1-7页

作者： Han, Rui Ng, Hui Khoon Englert, Berthold-Georg Natl Univ Singapore Ctr Quantum Technol Singapore 117543 Singapore Max Planck Inst Sci Light D-91058 Erlangen Germany Univ Erlangen Nurnberg Inst Opt Informat & Photon D-91058 Erlangen Germany Yale NUS Coll Singapore 138609 Singapore CNRS UNS NUS NTU Int Joint Res Unit UMI 3654 MajuLab Singapore Singapore Natl Univ Singapore Dept Phys Singapore 117542 Singapore

One can implement fast two-qubit entangling gates by exploiting the Rydberg blockade. Although various theoretical schemes have been proposed, experimenters have not yet been able to demonstrate two-atom gates of high fidelity due to experimental constraints. We propose a novel scheme, which only uses a single Rydberg pulse illuminating both atoms, for the construction of neutral-atom controlled-phase gates. In contrast to the existing schemes, our approach is simpler to implement and requires neither individual addressing of atoms nor adiabatic procedures. With parameters estimated based on actual experimental scenarios, a gate fidelity higher than 0.99 is achievable. Copyright (C) EPLA, 2016

关键词： quantum computation architectures and implementations Coherent control of atomic interactions with photons Rydberg states

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Virtual-Excitation Induced High-Dimensional State Transfer in a quantum Network

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INTERNATIONAL JOURNAL OF THEORETICAL PHYSICS 2016年第3期55卷 1361-1369页

作者： Chen, Ming-Feng Shen, Li-Tuo Chen, Rong-Xin Yang, Zhen-Biao Fuzhou Univ Dept Phys Fuzhou 350108 Peoples R China

We propose a scheme for quantum state transfer within the high-dimensional state subspaces between any two nodes in a quantum network. The states are encoded in the collective ground states of multiple atoms. The transfer processes are controlled by only applying external laser pulses. The prominent feature of the scheme is that the state transfer of any dimension can be achieved through virtually coupling all the excitations of the total system.

关键词： quantum information quantum computation architectures and implementations

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Implementing a distance-based classifier with a quantum interference circuit

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EPL 2017年第6期119卷 60002-60002页

作者： Schuld, M. Fingerhuth, M. Petruccione, F. Univ KwaZulu Natal Sch Chem & Phys Quantum Res Grp ZA-4000 Durban South Africa Univ Maastricht Maastricht Sci Programme NL-6200 MD Maastricht Netherlands Natl Inst Theoret Phys KwaZulu Natal ZA-4000 Durban South Africa

Lately, much attention has been given to quantum algorithms that solve pattern recognition tasks in machine learning. Many of these quantum machine learning algorithms try to implement classical models on large-scale universal quantum computers that have access to non-trivial subroutines such as Hamiltonian simulation, amplitude amplification and phase estimation. We approach the problem from the opposite direction and analyse a distance-based classifier that is realised by a simple quantum interference circuit. After state preparation, the circuit only consists of a Hadamard gate as well as two single-qubit measurements, and computes the distance between data points in quantum parallel. We demonstrate the proof of principle using the IBM quantum Experience and analyse the performance of the classifier with numerical simulations. Copyright (C) EPLA, 2017

关键词： quantum algorithms, protocols, and simulations quantum computation architectures and implementations

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Donors in Ge as qubits -Establishing physical attributes

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EPL 2016年第2期116卷 20002-20002页

作者： Baena, A. Saraiva, A. L. Menezes, Marcos G. Koiller, Belita Univ Fed Rio de Janeiro Inst Fis CP 68528 BR-21941972 Rio De Janeiro Brazil

quantum electronic devices at the single-impurity level demand the understanding of the physical attributes of dopants with an unprecedented accuracy. Germanium-based technologies have been developed recently, creating the necessity to adapt the latest theoretical tools to the unique electronic structure of this material. We investigate basic properties of donors in Ge which are not known experimentally, but are indispensable for qubit implementations. Our approach provides a description of the wave function at multiscale, associating microscopic information from density functional theory and envelope functions from state-of-the-art multivalley effective mass calculations, including a central-cell correction designed to reproduce the energetics of all group-V donor species (P, As, Sb and Bi). With this formalism, we predict the binding energies of negatively ionized donors (D-state). Furthermore, we investigate the signatures of buried donors to be expected from scanning tunneling microscopy (STM). The naive assumption that attributes of donor electrons in other semiconductors may be extrapolated to Ge is shown to fail, similarly to earlier attempts to recreate in Si qubits designed for GaAs. Our results suggest that the mature techniques available for qubit realizations may be adapted to germanium to some extent, but the peculiarities of the Ge band structure will demand new ideas for fabrication and control. Copyright (C) EPLA, 2016

关键词： quantum computation architectures and implementations Single particle states Scanning tunneling microscopes

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Fractionalized flux, Majorana fermions and non-Abelian anyons in topological superfluid on optical lattices

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EPL 2016年第1期116卷 13002-13002页

作者： Wu, Ya-Jie Kou, Su-Peng Xian Technol Univ Sch Sci Xian 710032 Peoples R China Beijing Normal Univ Dept Phys Beijing 100875 Peoples R China

Recently, topological excitations obeying non-Abelian statistics attracted intensive attention because of their exotic statistics and possible applications in topological quantum computation. In this paper, based on a topological s-wave superfluid on a Peierls lattice, we find fractionalized flux and non-Abelian anyons, and then give a realistic proposal to realize the universal topological quantum computation, and especially show how to perform the single-qubit gate-phase-shift gate. Finally, we discuss the experimental realization on optical lattices. Copyright (C) EPLA, 2016

关键词： Atoms in optical lattices Effects of crystal defects, doping and substitution quantum computation architectures and implementations

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Geometric quantum phase for displaced states for a particle with an induced electric dipole moment

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EPL 2016年第2期115卷 20001-20001页

作者： Lemos de Melo, J. Bakke, K. Furtado, C. Univ Fed Reconcavo Bahia Ctr Ciencias Exatas & Tecnol Cruz Das Almas BA Brazil Univ Fed Paraiba Dept Fis Caixa Postal 5008 BR-58051970 Joao Pessoa PB Brazil

Basing on the analogue Landau levels for a neutral particle possessing an induced electric dipole moment, we show that displaced states can be built in the presence of electric and magnetic fields. Besides, the Berry phase associated with these displaced quantum states is obtained by performing an adiabatic cyclic evolution in series of paths in parameter space. Copyright (C) EPLA, 2016

关键词： Phases: geometric, dynamic or topological quantum computation architectures and implementations Optical implementations of quantum information processing and transfer

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Frequency spectrum of a superconducting metadevice

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EPL 2016年第5期115卷 50004-50004页

作者： Blackburn, J. A. Cirillo, M. Gronbech-Jensen, N. Wilfrid Laurier Univ Phys & Comp Sci Waterloo ON Canada Univ Roma Tor Vergata Dipartimento Fis I-00133 Rome Italy Univ Roma Tor Vergata MINAS Lab I-00133 Rome Italy Univ Calif Davis Dept Math Davis CA 95616 USA Univ Calif Davis Dept Mech & Aerosp Engn Davis CA 95616 USA CNR SPIN Inst Genoa Italy

We report on a systematic analysis of the frequency spectrum of a system often considered for quantum computing purposes, metadevice applications, and high-sensitivity sensors, namely a superconducting loop interrupted by Josephson junctions, the core of an rf-SQUID. We analyze both the cases in which a single junction closes the superconducting loop and the one in which the single junction is replaced by a superconducting interferometer. Perturbation analysis is employed to display the variety of the solutions of the system and the implications of the results for the present interest in fundamental and applied research are analyzed. Copyright (C) EPLA, 2016

关键词： quantum computation architectures and implementations Tunneling phenomena, Josephson effects Josephson devices

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Optical simulator of the quantum Fourier transform

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EPL 2016年第2期114卷 20004-20004页

作者： Nam, Y. S. Bluemel, R. Wesleyan Univ Middletown CT 06459 USA

Experimental realizations of the quantum Fourier transform (QFT) are currently limited to n <= 3 qubits, which limits experimental tests of theoretical predictions of QFT performance under various noise conditions and their scaling in n. As a possible strategy to overcome this limitation, we show that an exact one-to-one correspondence exists between the QFT and a specially designed optical grating with a curved screen. This device allows the experimental simulation of the QFT, including defects, up to qubit numbers around n = 20, not currently accessible to direct quantum experimentation. The experimental realizability of the device is discussed. Copyright (C) EPLA, 2016

关键词： quantum computation architectures and implementations quantum chaos, semiclassical methods Optical processors, correlators, and modulators

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Effective Hamiltonian for two interacting double-dot exchange-only qubits and their controlled-NOT operations

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quantum INFORMATION PROCESSING 2015年第1期14卷 47-65页

作者： Ferraro, E. De Michielis, M. Fanciulli, M. Prati, E. IMM CNR Lab MDM I-20864 Agrate Brianza Italy Univ Milano Bicocca Dipartimento Sci Mat I-20126 Milan Italy

Double-dot exchange-only qubit represents a promising compromise between high speed and simple fabrication in solid-state implementations. A couple of interacting double-dot exchange-only qubits, each composed by three electrons distributed in a double quantum dot, is exploited to realize controlled-NOT (CNOT) operations. The effective Hamiltonian model of the composite system is expressed by only exchange interactions between pairs of spins. Consequently, the evolution operator has a simple form and represents the starting point for the research of sequences of operations that realize CNOT gates. Two different geometrical configurations of the pair are considered, and a numerical mixed simplex and genetic algorithm is used. We compare the nonphysical case in which all the interactions are controllable from the external and the realistic condition in which intra-dot interactions are fixed by the geometry of the system. In the latter case, we find the CNOT sequences for both the geometrical configurations and we considered a qubit system where electrons are electrostatically confined in two quantum dots in a silicon nanowire. The effects of the geometrical sizes of the nanowire and of the gates on the fundamental parameters controlling the qubit are studied by exploiting a spin-density-functional theory-based simulator. Consequently, CNOT gate performances are evaluated.

关键词： quantum computation architectures and implementations quantum dots Silicon devices

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