Virtual Journal of Quantum Information

Decoherence-free neutron interferometry

D. A. Pushin, M. Arif, and D. G. Cory
Perfect single-crystal neutron interferometers are adversely sensitive to environmental disturbances, particularly mechanical vibrations. The sensitivity to vibrations results from the slow velocity of thermal neutrons and the long measurement time that are encountered in a typical experiment. Conse ... [Phys. Rev. A 79, 053635 (2009)] published Thu May 21, 2009.

Collisional population transfer in trapped Yb ions

M. M. Schauer, J. R. Danielson, A.-T. Nguyen, L.-B. Wang, X. Zhao et al.
Long-lived metastable states of Yb ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of Yb ions into the long-lived F state by mea ... [Phys. Rev. A 79, 062705 (2009)] published Fri Jun 5, 2009.

A highly efficient two level diamond based single photon source

D. A. Simpson, E. Ampem-Lassen, B. C. Gibson, S. Trpkovski, F. M. Hossain et al.
An unexplored diamond defect center that is found to emit stable single photons at a measured rate of 1.6 MHz at room temperature is reported. The center, identified in chemical vapor deposition grown diamond crystals, exhibits a sharp zero phonon line at 734 nm with a full width at half maximum of ... [Appl. Phys. Lett. 94, 203107 (2009)] published Wed May 20, 2009.

Multimode quantum memory based on atomic frequency combs

Mikael Afzelius, Christoph Simon, Hugues de Riedmatten, and Nicolas Gisin
An efficient multimode quantum memory is a crucial resource for long-distance quantum communication based on quantum repeaters. We propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb (AFC). The spectral width of the AFC ... [Phys. Rev. A 79, 052329 (2009)] published Thu May 21, 2009.

Long-range surface-plasmon-polariton excitation at the quantum level

D. Ballester, M. S. Tame, C. Lee, J. Lee, and M. S. Kim
We provide the quantum-mechanical description of the excitation of long-range surface-plasmon polaritons (LRSPPs) on thin metallic strips. The excitation process consists of an attenuated-reflection setup, where efficient photon-to-LRSPP wave-packet transfer is shown to be achievable. For calculatin ... [Phys. Rev. A 79, 053845 (2009)] published Tue May 26, 2009.

Phase diffusion and locking in single-qubit lasers

Stephan Andre, Valentina Brosco, Alexander Shnirman, and Gerd Schon
Motivated by recent experiments, which demonstrated lasing and cooling of the electromagnetic field in an electrical resonator coupled to a superconducting qubit, we study the phase coherence and diffusion of the system in the lasing state. We also discuss phase locking and synchronization induced b ... [Phys. Rev. A 79, 053848 (2009)] published Tue May 26, 2009.

Why the two-pulse photon echo is not a good quantum memory protocol

Jerome Ruggiero, Jean-Louis Le Gouet, Christoph Simon, and Thierry Chaneliere
We consider in this paper a two-pulse photon echo sequence in the prospect of quantum light storage. We analyze the conditions where quantum storage could be realistically performed. We simply and analytically calculate the efficiency in that limit, and clarify the role of the exactly pi-rephasing p ... [Phys. Rev. A 79, 053851 (2009)] published Wed May 27, 2009.

Possibility of coherent phenomena such as Bloch oscillations with single photons via W states

Amit Rai and G. S. Agarwal
We examine the behavior of single photons at multiport devices and inquire if coherent effects are possible. In particular we study how single photons need to be manipulated in order to study coherent phenomena. We show that single photons need to be produced in W states which lead to vanishing mean ... [Phys. Rev. A 79, 053849 (2009)] published Wed May 27, 2009.

Slot-waveguide cavities for optical quantum information applications

Mark P. Hiscocks, Chun-Hsu Su, Brant C. Gibson, Andrew D. Greentree, Lloyd C. L. Hollenberg et al.
To take existing quantum optical experiments and devices into a more practical regimes requires the construction of robust, solid-state implementations. In particular, to observe the strong-coupling regime of tom-photon interactions requires very small cavities and large quality factors. Here we sho ... [Opt. Express 17, 7295 (2009)] published Mon May 18, 2009.

Swap gate and controlled swap gate based on a single resonant interaction with cavity quantum electrodynamics

Xiao-Qiang Shao, Li Chen, Shou Zhang, and Yong-Fang Zhao
A scheme for implementing a swap gate is proposed with atoms sent through a microwave cavity. This scheme can be directly generalized to realize the controlled swap gate through appropriate changes of the coupling constants between the atoms and cavity. Moreover, an N-qubit controlled swap gate can ... [Phys. Scr. 79, 065004 (2009)] published Wed Jun 10, 2009.

Formation of Ramsey fringes based on pulsed coherent light storage

Bo Yan, Yisheng Ma, and Yuzhu Wang
We propose a scheme of obtaining Ramsey fringes based on pulsed coherent optical information storage. Unlike the usual frequency references where the Ramsey fringes are obtained by detecting the population of a certain state, we get the Ramsey fringes by detecting the atomic coherence. The central l ... [Phys. Rev. A 79, 063820 (2009)] published Thu Jun 11, 2009.

Quantum gating on neutral atoms in low-Q cavities by a single-photon input-output process

Qiong Chen and Mang Feng
We investigate the possibility to achieve quantum gates using atoms confined in low-Q cavities by single-photon input-output process. Different from in high-Q cavities with strong coupling, we may accomplish universal quantum gates on the atoms by Faraday rotations. Our idea could be applied to mult ... [Phys. Rev. A 79, 064304 (2009)] published Mon Jun 15, 2009.

Flux-induced semiconducting behavior of a quantum network

Shreekantha Sil, Santanu K. Maiti, and Arunava Chakrabarti
We show that a diamond-shaped periodic network, recently proposed as a model of a spin filter [A. Aharony, O. Entin-Wohlman, Y. Tokura, and S. Katsumoto, Phys. Rev. B 78, 125328 (2008)], is capable of behaving as a p-type or an n-type semiconductor depending on a suitable choice of the on-site poten ... [Phys. Rev. B 79, 193309 (2009)] published Tue May 19, 2009.

Impact of classical forces and decoherence in multiterminal Aharonov-Bohm networks

E. Strambini, V. Piazza, G. Biasiol, L. Sorba, and F. Beltram
Multiterminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum networks (QNs) thanks to their ability to map input states into controlled coherent superpositions of output states. We report on experiments performed on three-terminal GaAs/AlGaAs AB devices and compare our results with a ... [Phys. Rev. B 79, 195443 (2009)] published Fri May 29, 2009.

Lehmann-Symanzik-Zimmermann reduction approach to multiphoton scattering in coupled-resonator arrays

T. Shi and C. P. Sun
We present a quantum field theoretical approach based on the Lehmann-Symanzik-Zimmermann reduction for the multiphoton scattering process in a nanoarchitecture consisting of the coupled-resonator arrays (CRA), which are also coupled to some artificial atoms as a controlling quantum node. By making u ... [Phys. Rev. B 79, 205111 (2009)] published Wed May 20, 2009.

Memory for Light as a Quantum Process

M. Lobino, C. Kupchak, E. Figueroa, and A. I. Lvovsky
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 ... [Phys. Rev. Lett. 102, 203601 (2009)] published Tue May 19, 2009.

Qubit Residence Time Measurements with a Bose-Einstein Condensate

D. Sokolovski
We show that an electrostatic qubit located near a Bose-Einstein condensate trapped in a symmetric double-well potential can be used to measure the duration the qubit has spent in one of its quantum states. The strong, medium, and weak measurement regimes are analyzed. The analogy between the reside ... [Phys. Rev. Lett. 102, 230405 (2009)] published Fri Jun 12, 2009.

Ultrafast Coherent Electron Spin Flip in a Modulation-Doped CdTe Quantum Well

Carey Phelps, Timothy Sweeney, Ronald T. Cox, and Hailin Wang
We report the experimental realization of coherent electron spin flip in a modulation-doped CdTe quantum well. Coherent spin rotation is realized with an off-resonant laser pulse, which induces a polarization-dependent optical Stark shift in the trion resonance. Complete electron spin flip is made p ... [Phys. Rev. Lett. 102, 237402 (2009)] published Fri Jun 12, 2009.

Universal Detector Efficiency of a Mesoscopic Capacitor

Simon E. Nigg and Markus Buttiker
We investigate theoretically a novel type of high frequency quantum detector based on the mesoscopic capacitor recently realized by Gabelli et al. [Science 313, 499 (2006)], which consists of a quantum dot connected via a single channel quantum point contact to a single lead. We show that the state ... [Phys. Rev. Lett. 102, 236801 (2009)] published Tue Jun 9, 2009.

Time-optimal performance of Josephson charge qubits: A process tomography approach

Robert Roloff and Walter Potz
A process tomography based optimization scheme for open quantum systems is used to determine the performance limits of Josephson charge qubits within current experimental means. The qubit is modeled microscopically as an open quantum system taking into account state leakage, as well as environment-i ... [Phys. Rev. B 79, 224516 (2009)] published Mon Jun 15, 2009.

Robust quantum repeater with atomic ensembles and single-photon sources

Fang-Yu Hong and Shi-Jie Xiong
We present an efficient scheme for generating high-fidelity entanglement locally which is essential for quantum repeater protocols. Two local polarization entangled states of atomic ensembles u and d are generated by absorbing a single photon emitted by on-demand single-photon sources, based on whic ... [Phys. Rev. A 79, 052341 (2009)] published Thu May 28, 2009.

Robust and fast geometric quantum computation with multiqubit gates in cavity QED

Gong-Wei Lin, Xu-Bo Zou, Xiu-Min Lin, and Guang-Can Guo
A scheme is proposed for realizing geometric quantum computation with one-qubit unitary gates and N-qubit (N>=2) phase gates in cavity QED. In the scheme, the cavity field and excited states are virtually excited by controlling appropriately atom-field couplings and engineering adiabatic passage; th ... [Phys. Rev. A 79, 064303 (2009)] published Tue Jun 9, 2009.

Ultracold molecules: vehicles to scalable quantum information processing

Kathy-Anne Brickman Soderberg, Nathan Gemelke, and Cheng Chin
In this paper, we describe a novel scheme to implement scalable quantum information processing using LiCs molecular states to entangle Li and Cs ultracold atoms held in independent optical lattices. The Li atoms will act as quantum bits to store information and Cs atoms will serve as messenger bits ... [New J. Phys. 11, 055022 (2009)] published Wed Jun 3, 2009.

Focus on Cold and Ultracold Molecules

Lincoln Carr and Jun Ye
Cold and ultracold molecules are the next wave of ultracold physics, giving rise to an exciting array of scientific opportunities, including many body physics for novel quantum phase transitions, new states of matter, and quantum information processing. Precision tests of fundamental physical laws ... [New J. Phys. 11, 055009 (2009)] published Wed Jun 3, 2009.

Molecular electron-spin quantum computers and quantum information processing: pulse-based electron magnetic resonance spin technology applied to matter spin-qubits

Kazunobu Sato, Shigeaki Nakazawa, Robabeh Rahimi, Tomoaki Ise, Shinsuke Nishida et al.
Pulse-based ElectronNuclear and ELectronelectron DOuble Resonance (ENDOR/ELDOR) techniques have been applied to molecular spins in order to implement ensemble electron spin-qubit based quantum computers/computing (QC) and quantum information processing (QIP) in the solid state. Pulsed ENDOR-based QC ... [J. Mater. Chem. 19, 3739 ] published .

Competing many-body interactions in systems of trapped ions

A. Bermudez, D. Porras, and M. A. Martin-Delgado
We propose and theoretically analyze an experimental configuration in which lasers induce three-spin interactions between trapped ions. By properly choosing the intensities and frequencies of the lasers, three-spin couplings may be dominant or comparable to two-spin terms and magnetic fields. In thi ... [Phys. Rev. A 79, 060303 (2009)] published Tue Jun 9, 2009.

Realizing a partial general quantum cloning machine with superconducting quantum-interference devices in a cavity QED

Bao-Long Fang, Zhen Yang, and Liu Ye
We propose a scheme for implementing a partial general quantum cloning machine with superconducting quantum-interference devices coupled to a nonresonant cavity. By regulating the time parameters, our system can perform optimal symmetric (asymmetric) universal quantum cloning, optimal symmetric (asy ... [Phys. Rev. A 79, 054308 (2009)] published Fri May 22, 2009.

Influence of modal loss on quantum state generation via cross-Kerr nonlinearity

D. Mogilevtsev, Tomas Tyc, and N. Korolkova
In this paper we investigate the influence of decoherence effects on quantum states generated as a result of the cross-Kerr nonlinear interaction between two modes. For Markovian losses (both photon loss and dephasing), a region of parameters when losses still do not lead to destruction of nonclassi ... [Phys. Rev. A 79, 053832 (2009)] published Mon May 18, 2009.

Nuclear spin qubits in a trapped-ion quantum computer

M. Feng, Y. Y. Xu, F. Zhou, and D. Suter
Physical systems must fulfill a number of conditions to qualify as useful quantum bits (qubits) for quantum-information processing, including ease of manipulation, long decoherence times, and high fidelity readout operations. Since these conditions are hard to satisfy with a single system, it may be ... [Phys. Rev. A 79, 052331 (2009)] published Fri May 22, 2009.

Quantum nondemolition photon detection in circuit QED and the quantum Zeno effect

Ferdinand Helmer, Matteo Mariantoni, Enrique Solano, and Florian Marquardt
We analyze the detection of itinerant photons using a quantum nondemolition measurement. An important example is the dispersive detection of microwave photons in circuit quantum electrodynamics, which can be realized via the nonlinear interaction between photons inside a superconducting transmission ... [Phys. Rev. A 79, 052115 (2009)] published Wed May 20, 2009.

Wigner function of pulsed fields by direct detection

Maria Bondani, Alessia Allevi, and Alessandra Andreoni
We present the reconstruction of the Wigner function of some classical pulsed optical states obtained by direct measurement of the detected-photon probability distributions of the state displaced by a coherent field. We use a photodetector endowed with internal gain, which is operated in the non-pho ... [Opt. Lett. 34, 1444 (2009)] published Mon May 18, 2009.

Cold and ultracold molecules: science, technology and applications

Lincoln Carr, David DeMille, Roman Krems, and Jun Ye
This paper presents a review of the current state of the art in the research field of cold and ultracold molecules. It serves as an introduction to the focus issue of New Journal of Physics on Cold and Ultracold Molecules and describes new prospects for fundamental research and technological develop ... [New J. Phys. 11, 055049 (2009)] published Wed Jun 3, 2009.

Synthesizing arbitrary quantum states in a superconducting resonator

Max Hofheinz, H. Wang, M. Ansmann, Radoslaw C. Bialczak, Erik Lucero et al.
The superposition principle is a fundamental tenet of quantum mechanics. It allows a quantum system to be `in two places at the same time', because the quantum state of a physical system can simultaneously include measurably different physical states. The preparation and use of such superposed stat ... [Nature 459, 546 (2009)] published Thu May 28, 2009.

Quantum photonics: Quantum optics on a chip

Dominic W. Berry and Howard M. Wiseman
Abstract not available. [Nat. Photonics 3, 317 (2009)] published Thu May 28, 2009.

Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments

V. V. Dobrovitski, A. E. Feiguin, R. Hanson, and D. D. Awschalom
We study the Rabi oscillations decay of a spin decohered by a spin bath whose internal dynamics is caused by dipolar coupling between the bath spins. The form and rate of decay as a function of the intrabath coupling is obtained analytically, and confirmed numerically. The complex form of decay smoo ... [Phys. Rev. Lett. 102, 237601 (2009)] published Tue Jun 9, 2009.

Optimal Surface-Electrode Trap Lattices for Quantum Simulation with Trapped Ions

Roman Schmied, Janus H. Wesenberg, and Dietrich Leibfried
Trapped ions offer long internal state (spin) coherence times and strong interparticle interactions mediated by the Coulomb force. This makes them interesting candidates for quantum simulation of coupled lattices. To this end, it is desirable to be able to trap ions in arbitrary conformations with p ... [Phys. Rev. Lett. 102, 233002 (2009)] published Tue Jun 9, 2009.

Electrically Detected Interferometry of Majorana Fermions in a Topological Insulator

A. R. Akhmerov, Johan Nilsson, and C. W. J. Beenakker
Majorana fermions are zero-energy quasiparticles that may exist in superconducting vortices and interfaces, but their detection is problematic since they have no charge. This is an obstacle to the realization of topological quantum computation, which relies on Majorana fermions to store qubits in a ... [Phys. Rev. Lett. 102, 216404 (2009)] published Thu May 28, 2009.

Probing Neutral Majorana Fermion Edge Modes with Charge Transport

Liang Fu and C. L. Kane
We propose two experiments to probe the Majorana fermion edge states that occur at a junction between a superconductor and a magnet deposited on the surface of a topological insulator. Combining two Majorana fermions into a single Dirac fermion on a magnetic domain wall allows the neutral Majorana f ... [Phys. Rev. Lett. 102, 216403 (2009)] published Thu May 28, 2009.

Coherence and Control of Quantum Registers Based on Electronic Spin in a Nuclear Spin Bath

P. Cappellaro, L. Jiang, J. S. Hodges, and M. D. Lukin
We consider a protocol for the control of few-qubit registers comprising one electronic spin embedded in a nuclear spin bath. We show how to isolate a few proximal nuclear spins from the rest of the bath and use them as building blocks for a potentially scalable quantum information processor. We des ... [Phys. Rev. Lett. 102, 210502 (2009)] published Fri May 29, 2009.

Electronic Refrigeration at the Quantum Limit

Andrey V. Timofeev, Meri Helle, Matthias Meschke, Mikko Mottonen, and Jukka P. Pekola
We demonstrate quantum-limited electronic refrigeration of a metallic island in a low-temperature microcircuit. We show that matching the impedance of the circuit enables refrigeration at a distance, of about 50 [mu]m in our case, through superconducting leads with a cooling power determined by the ... [Phys. Rev. Lett. 102, 200801 (2009)] published Mon May 18, 2009.

Coherent spin manipulations in Yb:CaWO at X- and W-band EPR frequencies

R. M. Rakhmatullin, I. N. Kurkin, G. V. Mamin, S. B. Orlinskii, M. R. Gafurov et al.
Coherent spin dynamics of impurity Yb ions in the CaWO single crystal has been studied using X- and W-band EPR. Rabi oscillations of the sample magnetization with damping times comparable to their period, driven by pulses of the microwave field with duration up to 5 [mu]s, were observed. The larges ... [Phys. Rev. B 79, 172408 (2009)] published Wed May 20, 2009.

Measurement of filling factor 5/2 quasiparticle interference with observation of charge e/4 and e/2 period oscillations

R. L. Willett, L. N. Pfeiffer, and K. W. West
A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices ma ... [Proc. Natl. Acad. Sci. U.S.A. 106, 8853 (2009)] published Wed Jun 3, 2009.

Coherent Rabi response of a charge-phase qubit under microwave irradiation

V. I. Shnyrkov, D. Born, A. A. Soroka, and W. Krech
We report on radio-frequency (rf) measurements of the charge-phase qubit being under continuous microwave irradiation in the state of weak coupling to a radio-frequency tank circuit. We studied the rf impedance dependence on the two important parameters such as the power of microwave irradiation, wh ... [Phys. Rev. B 79, 184522 (2009)] published Fri May 22, 2009.

Coupled donors in quantum dots: Quantum size and dielectric mismatch effects

J. L. Movilla, A. Ballester, and J. Planelles
Spatial and dielectric confinement modulations of the spontaneous emission rates, transition energies, and charge-density distributions of a singly ionized double donor system (D) in a spherical quantum dot are calculated within the framework of the effective-mass envelope function approximation. Di ... [Phys. Rev. B 79, 195319 (2009)] published Wed May 20, 2009.

Transverse-field-induced effects in carbon nanotubes

Wade DeGottardi, Tzu-Chieh Wei, and Smitha Vishveshwara
We investigate the properties of conduction electrons in single-walled armchair carbon nanotubes in the presence of both transverse electric and magnetic fields. We find that these fields provide a controlled means of tuning low-energy band-structure properties such as inducing gaps in the spectrum, ... [Phys. Rev. B 79, 205421 (2009)] published Thu May 21, 2009.

Chaotic dynamics of a Bose-Einstein condensate coupled to a qubit

J. Martin, B. Georgeot, and D. L. Shepelyansky
We study numerically the coupling between a qubit and a Bose-Einstein condensate (BEC) moving in a kicked optical lattice using Gross-Pitaevskii equation. In the regime where the BEC size is smaller than the lattice period, the chaotic dynamics of the BEC is effectively controlled by the qubit state ... [Phys. Rev. E 79, 066205 (2009)] published Fri Jun 12, 2009.

Local temperature in quantum thermal states

Artur Garcia-Saez, Alessandro Ferraro, and Antonio Acin
We consider blocks of quantum spins in a chain at thermal equilibrium, focusing on their properties from a thermodynamical perspective. In a classical system the temperature behaves as an intensive magnitude, above a certain block size, regardless of the actual value of the temperature itself. Howev ... [Phys. Rev. A 79, 052340 (2009)] published Thu May 28, 2009.

Optimal state discrimination in general probabilistic theories

Gen Kimura, Takayuki Miyadera, and Hideki Imai
We investigate a state discrimination problem in operationally the most general framework to use a probability, including both classical, quantum theories, and more. In this wide framework, introducing closely related family of ensembles (which we call a Helstrom family of ensembles) with the proble ... [Phys. Rev. A 79, 062306 (2009)] published Tue Jun 9, 2009.

Position and momentum tomography

Jukka Kiukas, Pekka Lahti, and Jussi Schultz
We illustrate the use of the statistical method of moments for determining the position and momentum distributions of a quantum object from the statistics of a single measurement. The method is used for three different, though related, models: the sequential measurement model, the Arthurs-Kelly mode ... [Phys. Rev. A 79, 052119 (2009)] published Tue May 26, 2009.

Contractivity of the Hilbert-Schmidt distance under open-system dynamics

Xiaoting Wang and S. G. Schirmer
It is shown that the Hilbert-Schmidt (HS) norm and distance, unlike the trace norm and distance, are generally not contractive for open quantum systems under Lindblad dynamics. Necessary and sufficient conditions for contractivity of the HS norm and distance are given, and explicit criteria in terms ... [Phys. Rev. A 79, 052326 (2009)] published Wed May 20, 2009.

Extending Hudson's theorem to mixed quantum states

A. Mandilara, E. Karpov, and N. J. Cerf
According to Hudson's theorem, any pure quantum state with a positive Wigner function is necessarily a Gaussian state. Here, we make a step toward the extension of this theorem to mixed quantum states by finding upper and lower bounds on the degree of non-Gaussianity of states with positive Wigner f ... [Phys. Rev. A 79, 062302 (2009)] published Wed Jun 3, 2009.

Convex trace functions on quantum channels and the additivity conjecture

Markus Muller
We study a natural generalization of the additivity problem in quantum information theory: given a pair of quantum channels, then what is the set of convex trace functions that attain their maximum on unentangled inputs if they are applied to the corresponding output state? We prove several results ... [Phys. Rev. A 79, 052332 (2009)] published Fri May 22, 2009.

Scaling of the fidelity susceptibility in a disordered quantum spin chain

N. Tobias Jacobson, Silvano Garnerone, Stephan Haas, and Paolo Zanardi
The phase diagram of a quantum XY spin chain with Gaussian-distributed random anisotropies and transverse fields is investigated, with focus on the fidelity susceptibility, a recently introduced quantum information theoretical measure. Monitoring the finite-size scaling of the probability distributi ... [Phys. Rev. B 79, 184427 (2009)] published Tue May 26, 2009.

Transitions in the Communication Capacity of Dissipative Qubit Channels

D. Daems
The information transmission is studied for quantum channels in which the noise includes dissipative effects, more specifically, nonunitality. Noise is usually a nuisance but can sometimes be helpful. For these channels, the communication capacity is shown to increase with the dissipative component ... [Phys. Rev. Lett. 102, 180503 (2009)] published Tue May 5, 2009.

Numerical solutions of the time-dependent Schrodinger equation: Reduction of the error due to space discretization

Hezhu Shao (邵和助) and Zhongcheng Wang (汪仲诚)
We present an improved space-discretization scheme for the numerical solutions of the time-dependent Schrodinger equation. Compared to the scheme of W. van Dijk and F. M. Toyama [Phys. Rev. E 75, 036707 (2007)], the present one, which contains more terms of second-order partial derivatives, greatly ... [Phys. Rev. E 79, 056705 (2009)] published Thu May 21, 2009.

Reverse Coherent Information

Raul Garcia-Patron, Stefano Pirandola, Seth Lloyd, and Jeffrey H. Shapiro
In this Letter we define a family of entanglement distribution protocols assisted by feedback classical communication that gives an operational interpretation to reverse coherent information, i.e., the symmetric counterpart of the well-known coherent information. This leads to the definition of a ne ... [Phys. Rev. Lett. 102, 210501 (2009)] published Fri May 29, 2009.

Localized Closed Timelike Curves Can Perfectly Distinguish Quantum States

Todd A. Brun, Jim Harrington, and Mark M. Wilde
We show that qubits traveling along closed timelike curves are a resource that a party can exploit to distinguish perfectly any set of quantum states. As a result, an adversary with access to closed timelike curves can break any prepare-and-measure quantum key distribution protocol. Our result also ... [Phys. Rev. Lett. 102, 210402 (2009)] published Wed May 27, 2009.

Unifying All Classical Spin Models in a Lattice Gauge Theory

G. De las Cuevas, W. Dur, H. J. Briegel, and M. A. Martin-Delgado
The partition function of all classical spin models, including all discrete standard statistical models and all Abelian discrete lattice gauge theories (LGTs), is expressed as a special instance of the partition function of the 4D [openface Z] LGT. This unifies all classical spin models with apparen ... [Phys. Rev. Lett. 102, 230502 (2009)] published Thu Jun 11, 2009.

Two-Qubit State Tomography Using a Joint Dispersive Readout

S. Filipp, P. Maurer, P. J. Leek, M. Baur, R. Bianchetti et al.
Quantum state tomography is an important tool in quantum information science for complete characterization of multiqubit states and their correlations. Here we report a method to perform a joint simultaneous readout of two superconducting qubits dispersively coupled to the same mode of a microwave t ... [Phys. Rev. Lett. 102, 200402 (2009)] published Fri May 22, 2009.

Optimal quantum multiparameter estimation and application to dipole- and exchange-coupled qubits

Kevin C. Young, Mohan Sarovar, Robert Kosut, and K. Birgitta Whaley
We consider the problem of quantum multiparameter estimation with experimental constraints and formulate the solution in terms of a convex optimization. Specifically, we outline an efficient method to identify the optimal strategy for estimating multiple unknown parameters of a quantum process and a ... [Phys. Rev. A 79, 062301 (2009)] published Tue Jun 2, 2009.

Unambiguous identification of coherent states. II. Multiple resources

Michal Sedlak, Mario Ziman, Vladimir Buzek, and Mark Hillery
We analyze unambiguous identification of coherent states of an electromagnetic field. In particular, we study possible generalizations of an optical setup proposed in Sedlak et al. [Phys. Rev. A 76, 022326 (2007)]. We show how the unambiguous identification of coherent states can be performed in a g ... [Phys. Rev. A 79, 062305 (2009)] published Tue Jun 9, 2009.

Effects of time delay in feedback control of linear quantum systems

K. Nishio, K. Kashima, and J. Imura
We investigate feedback control of linear quantum systems subject to feedback-loop time delays. In particular, we examine the relation between the potentially achievable control performance and the time delays and provide theoretical guidelines for the future experimental setup in two physical syste ... [Phys. Rev. A 79, 062105 (2009)] published Tue Jun 9, 2009.

Erratum: Performance of deterministic dynamical decoupling schemes: Concatenated and periodic pulse sequences [Phys. Rev. A 75, 062310 (2007)]

Kaveh Khodjasteh and Daniel A. Lidar
Abstract not available. [Phys. Rev. A 79, 069901 (2009)] published Fri Jun 5, 2009.

Nuclear State Preparation via Landau-Zener-Stuckelberg Transitions in Double Quantum Dots

Hugo Ribeiro and Guido Burkard
We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a ... [Phys. Rev. Lett. 102, 216802 (2009)] published Thu May 28, 2009.

Thresholds for Topological Codes in the Presence of Loss

Thomas M. Stace, Sean D. Barrett, and Andrew C. Doherty
Many proposals for quantum information processing are subject to detectable loss errors. In this Letter, we show that topological error correcting codes, which protect against computational errors, are also extremely robust against losses. We present analytical results showing that the maximum toler ... [Phys. Rev. Lett. 102, 200501 (2009)] published Mon May 18, 2009.

Resource requirements for fault-tolerant quantum simulation: The ground state of the transverse Ising model

Craig R. Clark, Tzvetan S. Metodi, Samuel D. Gasster, and Kenneth R. Brown
We estimate the resource requirements, the total number of physical qubits and computational time, required to compute the ground-state energy of a one-dimensional quantum transverse Ising model (TIM) of N spin-1/2 particles, as a function of the system size and the numerical precision. This estimat ... [Phys. Rev. A 79, 062314 (2009)] published Mon Jun 15, 2009.

Generalized concatenated quantum codes

Markus Grassl, Peter Shor, Graeme Smith, John Smolin, and Bei Zeng
We discuss the concept of generalized concatenated quantum codes. This generalized concatenation method provides a systematical way for constructing good quantum codes, both stabilizer codes and nonadditive codes. Using this method, we construct families of single-error-correcting nonadditive quantu ... [Phys. Rev. A 79, 050306 (2009)] published Fri May 22, 2009.

Memory coherence of a sympathetically cooled trapped-ion qubit

J. P. Home, M. J. McDonnell, D. J. Szwer, B. C. Keitch, D. M. Lucas et al.
We demonstrate sympathetic cooling of a Ca trapped-ion memory qubit by a Ca coolant ion sufficiently near the ground state of motion for fault-tolerant quantum logic, while maintaining coherence of the qubit. This is an essential ingredient in trapped-ion quantum computers. The isotope shifts are su ... [Phys. Rev. A 79, 050305 (2009)] published Fri May 22, 2009.

Reduced fidelity in topological quantum phase transitions

Erik Eriksson and Henrik Johannesson
We study the reduced fidelity between local states of lattice systems exhibiting topological order. By exploiting mappings to spin models with classical order, we are able to analytically extract the scaling behavior of the reduced fidelity at the corresponding quantum phase transitions out of the t ... [Phys. Rev. A 79, 060301 (2009)] published Wed Jun 3, 2009.

Creation and localization of entanglement in a simple configuration of coupled harmonic oscillators

J. F. Leandro and F. L. Semiao
We investigate a simple arrangement of coupled harmonic oscillators which brings out some interesting effects concerning creation of entanglement. It is well known that if each member in a linear chain of coupled harmonic oscillators is prepared in a classical state, such as a pure coherent state or ... [Phys. Rev. A 79, 052334 (2009)] published Tue May 26, 2009.

Entanglement preservation by continuous distillation

D. Mundarain and M. Orszag
We study the two-qubit entanglement preservation for a system in the presence of independent thermal baths. We use a combination of filtering operations and distillation protocols as a series of frequent measurements on the system. It is shown that a small fraction of the total amount of available c ... [Phys. Rev. A 79, 052333 (2009)] published Fri May 22, 2009.

Achieving multipartite entanglement of distant atoms through selective photon emission and absorption processes

Xin-You Lu, Liu-Gang Si, Xiang-Ying Hao, and Xiaoxue Yang
We propose two schemes for deterministically generating three-partite Greenberger-Horne-Zeilinger (GHZ) and W states of distant atoms based on the selective photon emission and absorption processes. In our schemes, it is found that the effects of atomic spontaneous decay and photon leakage out of fi ... [Phys. Rev. A 79, 052330 (2009)] published Thu May 21, 2009.

Measurement-based synthesis of multiqubit entangled states in superconducting cavity QED

Ferdinand Helmer and Florian Marquardt
Entangled multiqubit states may be generated through a dispersive collective quantum nondemolition measurement of superconducting qubits coupled to a microwave transmission line resonator. Using the quantum trajectory approach, we analyze the stochastic measurement traces that would be observed in e ... [Phys. Rev. A 79, 052328 (2009)] published Wed May 20, 2009.

Correlation matrices of two-mode bosonic systems

Stefano Pirandola, Alessio Serafini, and Seth Lloyd
We present a detailed analysis of all the algebraic conditions an arbitrary 4 x 4 symmetric matrix must satisfy in order to represent the correlation matrix of a two-mode bosonic system. Then, we completely clarify when this arbitrary matrix can represent the correlation matrix of a separable or ent ... [Phys. Rev. A 79, 052327 (2009)] published Wed May 20, 2009.

Entanglement sudden death as an indicator of fidelity in a four-qubit cluster state

Yaakov S. Weinstein
I explore the entanglement evolution of a four-qubit cluster state in a dephasing environment concentrating on the phenomenon of entanglement sudden death (ESD). Specifically, I ask whether the onset of ESD has an effect on the utilization of this cluster state as a means of implementing a single-qu ... [Phys. Rev. A 79, 052325 (2009)] published Tue May 19, 2009.

Two-dimensional cluster-state preparation with linear ion traps

Harald Wunderlich, Christof Wunderlich, Kilian Singer, and Ferdinand Schmidt-Kaler
We present schemes to prepare two-dimensional cluster states [H. J. Briegel and R. Raussendorf, Phys. Rev. Lett. 86, 910 (2001)] with atomic ions confined in a microstructured linear ion trap and coupled by an engineered spin-spin interaction. In particular, we show how to prepare a n x 2 cluster st ... [Phys. Rev. A 79, 052324 (2009)] published Mon May 18, 2009.

Creation of high-quality long-distance entanglement with flexible resources

Bing He, Yuhang Ren, and Janos A. Bergou
We present a quantum repeater protocol that generates the elementary segments of entangled photons through the communication of qubus in coherent states. The input photons at the repeater stations can be in arbitrary states to save the local state preparation time for the operations. The flexibility ... [Phys. Rev. A 79, 052323 (2009)] published Mon May 18, 2009.

Environment-dependent dissipation in quantum Brownian motion

J. Paavola, J. Piilo, K.-A. Suominen, and S. Maniscalco
The dissipative dynamics of a quantum Brownian particle is studied for different types of environment. We derive analytic results for the time evolution of the mean energy of the system for Ohmic, sub-Ohmic, and super-Ohmic environments, without performing the Markovian approximation. Our results al ... [Phys. Rev. A 79, 052120 (2009)] published Tue May 26, 2009.

Experimental demonstration of a teleportation-based programmable quantum gate

Lukas SlodiCka, Miroslav Jezek, and Jaromir Fiurasek
We experimentally demonstrate a programmable quantum gate that applies a sign flip operation to data qubit in an arbitrary basis fully specified by the quantum state of a two-qubit program register. Our linear-optical implementation is inspired by teleportation-based schemes for quantum computing an ... [Phys. Rev. A 79, 050304 (2009)] published Thu May 21, 2009.

Entanglement signature in the mode structure of a single photon

C. Di Fidio and W. Vogel
It is shown that entanglement, which is a quantum correlation property of at least two subsystems, is imprinted in the mode structure of a single photon. The photon, which is emitted by two coupled cavities, carries the information on the concurrence of the two intracavity fields. This can be useful ... [Phys. Rev. A 79, 050303 (2009)] published Wed May 20, 2009.

Stable generation of quadrature entanglement using a ring interferometer

Yujiro Eto, Akihiro Nonaka, Yun Zhang, and Takuya Hirano
We propose and demonstrate a scheme to stably generate quadrature-entangled optical pulses using a ring interferometer composed of an optical parametric amplifier and a dispersive media. The entangled light pulses at telecommunication wavelength are generated by combining two squeezed beams. In our ... [Phys. Rev. A 79, 050302 (2009)] published Mon May 18, 2009.

Coherent state description of the ground state in the TavisCummings model and its quantum phase transitions

Octavio Castanos, Ramon Lopez-Pena, Eduardo Nahmad-Achar, Jorge Hirsch, Enrique Lopez-Moreno et al.
Quantum phase transitions and observables of interest of the ground state in the TavisCummings model are analyzed, for any number of atoms, by using a tensorial product of coherent states. It is found that this `trial' state constitutes a very good approximation to the exact quantum solution, in tha ... [Phys. Scr. 79, 065405 (2009)] published Wed Jun 10, 2009.

Extraction of pure entangled states from many-body systems by distant local projections

J. Molina, H. Wichterich, V. E. Korepin, and S. Bose
We study the feasibility of extracting a pure entangled state of noncomplementary and potentially well-separated regions of a quantum many-body system. It is shown that this can indeed be accomplished in nonequilibrium scenarios as well as the ground state of the considered spin chain models when on ... [Phys. Rev. A 79, 062310 (2009)] published Thu Jun 11, 2009.

Two computable sets of multipartite entanglement measures

Beatrix C. Hiesmayr, Marcus Huber, and Philipp Krammer
We present two sets of computable entanglement measures for multipartite systems where each subsystem can have different degrees of freedom (so-called qudits). One set, called separability measure, reveals which of the subsystems are separable or entangled. For that we have to extend the concept of ... [Phys. Rev. A 79, 062308 (2009)] published Wed Jun 10, 2009.

Spectrum conditions for symmetric extendible states

Geir Ove Myhr and Norbert Lutkenhaus
We analyze bipartite quantum states that admit a symmetric extension. Any such state can be decomposed into a convex combination of states that allow a pure symmetric extension. A necessary condition for a state to admit a pure symmetric extension is that the spectra of the local and global density ... [Phys. Rev. A 79, 062307 (2009)] published Tue Jun 9, 2009.

Multiparameter entangled-state engineering using adaptive optics

Cristian Bonato, David Simon, Paolo Villoresi, and Alexander V. Sergienko
We investigate how quantum coincidence interferometry is affected by a controllable manipulation of transverse wave vectors in type-II parametric down-conversion using adaptive optics techniques. In particular, we discuss the possibility of spatial walk-off compensation in quantum interferometry and ... [Phys. Rev. A 79, 062304 (2009)] published Fri Jun 5, 2009.

Conditions for factorizable output from a beam splitter

S. C. Springer, Jinhyoung Lee, M. Bellini, and M. S. Kim
A beam splitter is one of the most important devices in an optics laboratory because of its handiness and versatility; equivalent devices are found in various quantum systems to couple two subsystems or to interfere them. While it is normal that two independent input fields are superposed at the bea ... [Phys. Rev. A 79, 062303 (2009)] published Wed Jun 3, 2009.

Spontaneously generated atomic entanglement in free space reinforced by incoherent pumping

Ling Zhou, Guo Hui Yang, and Anil K. Patnaik
We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited-state lifetime ... [Phys. Rev. A 79, 062102 (2009)] published Fri Jun 5, 2009.

Preparation and identification of two-photon positively-momentum-correlated entangled states

Wei-Tao Liu (刘伟涛), Ping-Xing Chen (陈平形), Cheng-Zu Li (李承祖), and Jian-Min Yuan (袁建民)
Einstein, Podolsky, and Rosen brought up a state with momenta of two particles anticorrelated, which introduced the concept of entanglement and excited many interesting studies. In contrast, we propose an experimental scheme to prepare and identify two-photon momentum positively correlated entanglem ... [Phys. Rev. A 79, 061802 (2009)] published Fri Jun 12, 2009.

Entanglement localization after coupling to an incoherent noisy system

Fabio Sciarrino, Eleonora Nagali, Francesco De Martini, Miroslav Gavenda, and Radim Filip
We report the experimental realization of entanglement localization which restores the polarization entanglement completely redirected after a linear coupling with incoherent and noisy surrounding photon. The method based only on measurements of the surrounding photon after the coupling and on posts ... [Phys. Rev. A 79, 060304 (2009)] published Wed Jun 10, 2009.

Exploiting quench dynamics in spin chains for distant entanglement and quantum communication

Hannu Wichterich and Sougato Bose
We suggest a method of entangling significantly the distant ends of a spin chain using minimal control. This entanglement between distant individual spins is brought about solely by exploiting the dynamics of an initial mixed state with Neel order if the lattice features nearest-neighbor XXZ interac ... [Phys. Rev. A 79, 060302 (2009)] published Thu Jun 4, 2009.

Monogamy of entanglement and teleportation capability

Soojoon Lee and Jungjoon Park
The monogamy inequality in terms of the concurrence, called the Coffman-Kundu-Wootters inequality [V. Coffman et al., Phys. Rev. A 61, 052306 (2000)], and its generalization [T. J. Osborne and F. Verstraete, Phys. Rev. Lett. 96, 220503 (2006)] hold on general n-qubit states including mixed ones. In ... [Phys. Rev. A 79, 054309 (2009)] published Thu May 28, 2009.

Global versus local quantum squeezing in composite systems

Yang Yang, Wanfang Liu, Zhe Sun, and Xiaoguang Wang
We investigate relations between the global squeezing of composite systems and the local squeezing of subsystems. For the pure symmetric product states, the global squeezing parameter is found to be equal to the local one for both spin and bosonic systems. Hence, a pure symmetric state is entangled ... [Phys. Rev. A 79, 054104 (2009)] published Fri May 29, 2009.

Modal, spectral, and polarization entanglement in guided-wave parametric down-conversion

Mohammed F. Saleh, Bahaa E. A. Saleh, and Malvin Carl Teich
We examine the modal, spectral, and polarization entanglement properties of photon pairs generated in a nonlinear periodically poled two-mode waveguide (one-dimensional planar or two-dimensional circular) via nondegenerate spontaneous parametric down-conversion. Any of the possible degrees of freedo ... [Phys. Rev. A 79, 053842 (2009)] published Thu May 21, 2009.

Intrinsic phase coherence of laser light

David T. Pegg
We examine the phase relationships between different packets of a beam of light emitted from a cavity through a partially transmitting mirror. We find that the beam has a pronounced phase coherence even when the intracavity field has a completely indeterminate phase such as, for example, when it is ... [Phys. Rev. A 79, 053837 (2009)] published Tue May 19, 2009.

Comparative study of dynamical simulation methods for the dissociation of molecular Bose-Einstein condensates

S. L. W. Midgley, S. Wuster, M. K. Olsen, M. J. Davis, and K. V. Kheruntsyan
We describe a pairing mean-field theory related to the Hartree-Fock-Bogoliubov approach, and apply it to the dynamics of dissociation of a molecular Bose-Einstein condensate into correlated bosonic atom pairs. We also perform the same simulation using two stochastic phase-space techniques for quantu ... [Phys. Rev. A 79, 053632 (2009)] published Wed May 20, 2009.

Storage of polarization-encoded cluster states in an atomic system

Chun-Hua Yuan, Li-Qing Chen, and Weiping Zhang
We present a scheme for entanglement of macroscopic atomic ensembles which are four spatially separate regions of an atomic cloud using cluster-correlated beams. We show that the cluster-type polarization-encoded entanglement could be mapped onto the long-lived collective ground state of the atomic ... [Phys. Rev. A 79, 052342 (2009)] published Fri May 29, 2009.

Characterizing the geometrical edges of nonlocal two-qubit gates

S. Balakrishnan and R. Sankaranarayanan
Nonlocal two-qubit gates are geometrically represented by tetrahedron known as Weyl chamber within which perfect entanglers form a polyhedron. We identify that all edges of the Weyl chamber and polyhedron are formed by single parametric gates. Nonlocal attributes of these edges are characterized usi ... [Phys. Rev. A 79, 052339 (2009)] published Thu May 28, 2009.

Experimental measurement of lower and upper bounds of concurrence for mixed quantum states

Yun-Feng Huang, Xiao-Ling Niu, Yan-Xiao Gong, Jian Li, Liang Peng et al.
We experimentally measure the lower and upper bounds of concurrence for a set of two-qubit mixed quantum states using photonic systems. The measured concurrence bounds are in agreement with the results evaluated from the density matrices reconstructed through quantum state tomography. In our experim ... [Phys. Rev. A 79, 052338 (2009)] published Wed May 27, 2009.

Thermal entanglement witness for materials with variable local spin lengths

Andre M. C. Souza and Francisco A. G. Almeida
We show that the thermal entanglement in a spin system using only magnetic-susceptibility measurements is restricted to the insulator materials. We develop a generalization of the thermal entanglement witness that allows us to get information about the system entanglement with variable local spin le ... [Phys. Rev. A 79, 052337 (2009)] published Wed May 27, 2009.

Interferometric distillation and determination of unknown two-qubit entanglement

S.-S. B. Lee and H.-S. Sim
We propose a scheme for both distilling and quantifying entanglement, applicable to individual copies of an arbitrary unknown two-qubit state. It is realized in a usual two-qubit interferometry with local filtering. Proper filtering operation for the maximal distillation of the state is achieved by ... [Phys. Rev. A 79, 052336 (2009)] published Wed May 27, 2009.

Pairwise quantum correlation formed in an ensemble of atomic two-level systems storing squeezed light

Kaoru Shimizu and Daisuke Hashimoto
This paper characterizes a quantum correlation formed in an ensemble of atomic two-level systems that stores a narrow-band squeezed state of light by coherently trapping an electron in an atomic superposed state a|1>+b|0>. In the storage process, a photonic quantum correlation in the squeezed light ... [Phys. Rev. A 79, 062312 (2009)] published Mon Jun 15, 2009.

Quantum mechanical evolution towards thermal equilibrium

Noah Linden, Sandu Popescu, Anthony J. Short, and Andreas Winter
The circumstances under which a system reaches thermal equilibrium, and how to derive this from basic dynamical laws, has been a major question from the very beginning of thermodynamics and statistical mechanics. Despite considerable progress, it remains an open problem. Motivated by this issue, we ... [Phys. Rev. E 79, 061103 (2009)] published Thu Jun 4, 2009.

Quantum phase transitions in a two-dimensional quantum XYX model: Ground-state fidelity and entanglement

Bo Li, Sheng-Hao Li, and Huan-Qiang Zhou
A systematic analysis is performed for quantum phase transitions in a two-dimensional anisotropic spin-1/2 antiferromagnetic XYX model in an external magnetic field. With the help of an innovative tensor network algorithm, we compute the fidelity per lattice site to demonstrate that the field-induce ... [Phys. Rev. E 79, 060101 (2009)] published Mon Jun 1, 2009.

Classical and quantum interference in multiband optical Bloch oscillations

Stefano Longhi
Classical and quantum interference of light propagating in arrays of coupled waveguides and undergoing multiband optical Bloch oscillations (BOs) with negligible Zener tunneling is theoretically investigated. In particular, it is shown that Mach-Zehnder-like interference effects spontaneously arise ... [Phys. Rev. B 79, 245108 (2009)] published Thu Jun 4, 2009.

Generation of entangled photon pairs from a single quantum dot embedded in a planar photonic-crystal cavity

P. K. Pathak and S. Hughes
We present a formal theory of single quantum dot coupling to a planar photonic crystal that supports quasidegenerate cavity modes and use this theory to describe and optimize entangled-photon pair generation via the biexciton-exciton cascade. In the generated photon pairs, either both photons are sp ... [Phys. Rev. B 79, 205416 (2009)] published Mon May 18, 2009.

Exact entanglement renormalization for string-net models

Robert Konig, Ben W. Reichardt, and Guifre Vidal
We construct an explicit renormalization-group transformation for Levin and Wen's string-net models on a hexagonal lattice. The transformation leaves invariant the ground-state fixed-point wave function of the string-net condensed phase. Our construction also produces an exact representation of the ... [Phys. Rev. B 79, 195123 (2009)] published Tue May 26, 2009.

Exploring frustrated spin systems using projected entangled pair states

V. Murg, F. Verstraete, and J. I. Cirac
We study the nature of the ground state of the frustrated JJ model and the JJ model using a variational algorithm based on projected entangled pair states. By investigating spin-spin correlation functions, we observe a separation in parameter regions with long- and short-range order. A direct compar ... [Phys. Rev. B 79, 195119 (2009)] published Wed May 20, 2009.

Two-stream instability in quasi-one-dimensional Bose-Einstein condensates

H. Tercas, J. T. Mendonca, and G. R. M. Robb
We apply a kinetic model to predict the existence of an instability mechanism in elongated Bose-Einstein condensates. Our kinetic description, based on the Wigner formalism, is employed to highlight the existence of unstable Bogoliubov waves that may be excited in the counterpropagation configuratio ... [Phys. Rev. A 79, 065601 (2009)] published Tue Jun 2, 2009.

Adaptive quantum teleportation

Joanna Modlawska and Andrzej Grudka
We consider multiple teleportation in the Knill-Laflamme-Milburn (KLM) scheme. We introduce adaptive teleportation, i.e., such that the choice of entangled state used in the next teleportation depends on the results of the measurements performed during the previous teleportations. We show that adapt ... [Phys. Rev. A 79, 064302 (2009)] published Fri Jun 5, 2009.

Distillability of entanglement in accelerated frames

Shahpoor Moradi
We study the entanglement distillability of bipartite mixed states of two modes of a free Dirac field as seen by two relatively accelerated parties. It is shown that there are states that will change from distillable into separable for a certain value of acceleration. We exemplify these criteria in ... [Phys. Rev. A 79, 064301 (2009)] published Fri Jun 5, 2009.

Extra phase noise from thermal fluctuations in nonlinear optical crystals

J. E. S. Cesar, A. S. Coelho, K. N. Cassemiro, A. S. Villar, M. Lassen et al.
We show theoretically and experimentally that scattered light by thermal phonons inside a second-order nonlinear crystal is the source of additional phase noise observed in optical parametric oscillators. This additional phase noise reduces the quantum correlations and has hitherto hindered the dire ... [Phys. Rev. A 79, 063816 (2009)] published Thu Jun 11, 2009.

Effect of dephasing on quantum features of the cavity radiation of an externally pumped correlated emission laser

Sintayehu Tesfa
Analysis of the effects of dephasing on quantum features of the cavity radiation of externally pumped correlated emission laser is presented. It turns out that entanglement and nonclassical photon number correlations are strongly reliant on the rate at which the atomic coherent superposition decays ... [Phys. Rev. A 79, 063815 (2009)] published Wed Jun 10, 2009.

Interference-induced enhancement of field entanglement from an intracavity three-level [bold-sans-serif V]-type atom

Hua-tang Tan, Hong-xing Xia, and Gao-xiang Li
We investigate the generation of two-mode-entangled light from a laser-driven three-level [bold-sans-serif V]-type atom inside a cavity by taking into account spontaneously generated quantum interference between two atomic decay channels. We show that under some conditions, the system can reduce to ... [Phys. Rev. A 79, 063805 (2009)] published Tue Jun 2, 2009.

Quantum ground-state cooling and tripartite entanglement with three-mode optoacoustic interactions

H. Miao, C. Zhao, L. Ju, and D. G. Blair
We present a quantum analysis of three-mode optoacoustic parametric interactions in an optical cavity, in which two orthogonal transverse optical-cavity modes are coupled to one acoustic mode through radiation pressure. Due to the optimal frequency matchingthe frequency separation of two cavity mode ... [Phys. Rev. A 79, 063801 (2009)] published Mon Jun 1, 2009.

Calculation of drag and superfluid velocity from the microscopic parameters and excitation energies of a two-component Bose-Einstein condensate in an optical lattice

Jacob Linder and Asle Sudbo
We investigate a model of a two-component Bose-Einstein condensate residing in an optical lattice. Within a Bogoliubov approach at the mean-field level, we derive exact analytical expressions for the excitation spectrum of the two-component condensate when taking into account hopping and interaction ... [Phys. Rev. A 79, 063610 (2009)] published Thu Jun 4, 2009.

Generation of tripartite states of flying electronic qubits and their characterization by energy measurements

S. Parida and N. Chandra
A scheme for generating states of three free electrons entangled with respect to their spins is suggested. It consists of sequential ejection of two Auger electrons (e and e) in the nonradiative decay of an inner-shell vacancy created due to the emission of photoelectron e from an atom, say A. In th ... [Phys. Rev. A 79, 062501 (2009)] published Mon Jun 1, 2009.

Non-BornOppenheimer electronic and nuclear wavepacket dynamics

Takehiro Yonehara, Satoshi Takahashi, and Kazuo Takatsuka
A practical quantum theory for unifying electronic and nuclear dynamics, which were separated by the BornOppenheimer approximation, is proposed. The theory consists of two processes. Nonadiabatic (quantum) electron wavepacket dynamics on branching (non-BornOppenheimer) nuclear paths are first constr ... [J. Chem. Phys. 130, 214113 (2009)] published Fri Jun 5, 2009.

Determining the Dynamics of Entanglement

O. Jimnez Faras, C. Lombard Latune, S. P. Walborn, L. Davidovich, and P. H. Souto Ribeiro
The estimation of the entanglement of multipartite systems undergoing decoherence is important for assessing the robustness of quantum information processes. It usually requires access to the final state and its full reconstruction through quantum tomography. General dynamical laws may simplify this ... [Science 324, 1414 (2009)] published Wed Jun 10, 2009.

Magnetic Field Sensing Beyond the Standard Quantum Limit Using 10-Spin NOON States

Jonathan A. Jones, Steven D. Karlen, Joseph Fitzsimons, Arzhang Ardavan, Simon C. Benjamin et al.
Quantum entangled states can be very delicate and easily perturbed by their external environment. This sensitivity can be harnessed in measurement technology to create a quantum sensor with a capability of outperforming conventional devices at a fundamental level. We compared the magnetic field sens ... [Science 324, 1166 (2009)] published Thu May 28, 2009.

Classical Analogues of Two-Photon Quantum Interference

R. Kaltenbaek, J. Lavoie, and K. J. Resch
Chirped-pulse interferometry (CPI) captures the metrological advantages of quantum Hong-Ou-Mandel (HOM) interferometry in a completely classical system. Modified HOM interferometers are the basis for a number of seminal quantum-interference effects. Here, the corresponding modifications to CPI allow ... [Phys. Rev. Lett. 102, 243601 (2009)] published Mon Jun 15, 2009.

Quantum Teleportation of the Temporal Fluctuations of Light

Changsuk Noh, A. Chia, Hyunchul Nha, M. J. Collett, and H. J. Carmichael
A scheme for the teleportation of a beam of light including its temporal fluctuations is proposed. Expressions for the teleported degrees of first- and second-order optical coherence are presented. Teleportation of an antibunched photon stream illustrates the proposal. ... [Phys. Rev. Lett. 102, 230501 (2009)] published Wed Jun 10, 2009.

X Entanglement: The Nonfactorable Spatiotemporal Structure of Biphoton Correlation

A. Gatti, E. Brambilla, L. Caspani, O. Jedrkiewicz, and L. A. Lugiato
We investigate the spatiotemporal structure of the biphoton entanglement in parametric down-conversion (PDC) and we demonstrate its nonfactorable X-shaped geometry. Such a structure gives access to the ultrabroad bandwidth of PDC, and can be exploited to achieve a biphoton temporal localization in t ... [Phys. Rev. Lett. 102, 223601 (2009)] published Thu Jun 4, 2009.

Stationary state entanglement of a one-atom two-field system under random phase telegraph noise

Aliekber Aktag and Hunkar Kayhan
In this paper, a system consisting of one atom coupled to two identical optical cavities in a stochastic interaction is investigated for the entanglement properties between the constituents by the JaynesCummings model. The noise is considered to be the random phase telegraph noise and an exact solut ... [Phys. Scr. 79, 065015 (2009)] published Wed Jun 10, 2009.

An introduction to the tomographic picture of quantum mechanics

A Ibort, V Man'ko, G Marmo, A Simoni, and F Ventriglia
Starting from the famous Pauli problem on the possibility of associating quantum states with probabilities, the formulation of quantum mechanics in which quantum states are described by fair probability distributions (tomograms, i.e. tomographic probabilities) is reviewed in a pedagogical style. The ... [Phys. Scr. 79, 065013 (2009)] published Wed Jun 10, 2009.

Conditions to preserve quantum entanglement of quadrature fluctuation fields in electromagnetically induced transparency media

You-Lin Chuang and Ray-Kuang Lee
We study the propagation of quantum fields through an electromagnetically induced transparency (EIT) medium with initially two squeezed and one coherent states. Conditions to preserve and to establish nonseparation criteria for perturbed quantized fluctuation fields are demonstrated. The results in ... [Opt. Lett. 34, 1537 (2009)] published Thu May 28, 2009.

A versatile waveguide source of photon pairs for chip-scale quantum information processing

Jun Chen, Aaron J. Pearlman, Alexander Ling, Jingyun Fan, and Alan L. Migdall
We demonstrate a bright, bandwidth-tunable, quasi-phase-matched single-waveguide source generating photon pairs near 900 nm and 1300 nm. Two-photon coincidence spectra are measured at a range of operatingtemperatures of a periodically-poled KTiOPO (PPKTP) waveguide, which supports both type-0 and ty ... [Opt. Express 17, 6727 (2009)] published Mon May 18, 2009.

Positive maps, majorization, entropic inequalities and detection of entanglement

R Augusiak and J Stasinska
In this paper, we discuss some general connections between the notions of positive map, weak majorization and entropic inequalities in the context of detection of entanglement among bipartite quantum systems. First, basing on the fact that any positive map [Formula: see text] can be written as the d ... [New J. Phys. 11, 053018 (2009)] published Wed Jun 3, 2009.

Entangled mechanical oscillators

J. D. Jost, J. P. Home, J. M. Amini, D. Hanneke, R. Ozeri et al.
Hallmarks of quantum mechanics include superposition and entanglement. In the context of large complex systems, these features should lead to situations as envisaged in the `Schrodinger's cat' thought experiment (where the cat exists in a superposition of alive and dead states entangled with a radi ... [Nature 459, 683 (2009)] published Thu Jun 4, 2009.

Vortex nucleation as a case study of symmetry breaking in quantum systems

D. Dagnino, N. Barberan, M. Lewenstein, and J. Dalibard
Mean-field methods are a very powerful tool for investigating weakly interacting many-body systems in many branches of physics. In particular, they describe with excellent accuracy trapped BoseEinstein condensates. A generic, but difficult question concerns the relation between the symmetry properti ... [Nature Phys. 5, 431 (2009)] published Wed Jun 3, 2009.

Cooper-pair-mediated coherence between two normal metals

P. Cadden-Zimansky, J. Wei, and V. Chandrasekhar
Two electrons bound in a singlet state have long provided a conceptual and pedagogical framework for understanding the non-local nature of entangled quantum objects. As bound singlet electrons separated by a coherence length of up to several hundred nanometres occur naturally in conventional Bardee ... [Nature Phys. 5, 393 (2009)] published Wed Jun 3, 2009.

High-fidelity transmission of entanglement over a high-loss free-space channel

Alessandro Fedrizzi, Rupert Ursin, Thomas Herbst, Matteo Nespoli, Robert Prevedel et al.
Quantum entanglement enables tasks not possible in classical physics. Many quantum communication protocols require the distribution of entangled states between distant parties. Here, we experimentally demonstrate the successful transmission of an entangled photon pair over a 144 km free-space link. ... [Nature Phys. 5, 389 (2009)] published Wed Jun 3, 2009.

Manipulation of multiphoton entanglement in waveguide quantum circuits

Jonathan C. F. Matthews, Alberto Politi, Andre Stefanov, and Jeremy L. O'Brien
On-chip integrated photonic circuits are crucial to further progress towards quantum technologies and in the science of quantum optics. Here we report precise control of single photon states and multiphoton entanglement directly on-chip. We manipulate the state of path-encoded qubits using integrate ... [Nat. Photonics 3, 346 (2009)] published Thu May 28, 2009.

Adiabatic passage scheme for entanglement between two distant microwave cavities interacting with single-molecule magnets

Xin-You Lu, Li-Li Zheng, Pei Huang, Jin Li, and Xiaoxue Yang
We propose a scheme for deterministically generating entanglement between two distant microwave cavities that interact with two single-molecule magnets (SMMs) and are connected by an optical fiber. In our scheme, the spontaneous decay of SMMs and photons damping in the fiber are efficiently suppress ... [J. Opt. Soc. Am. B 26, 1162 (2009)] published Mon Jun 15, 2009.

Quantum number theoretic transforms on multipartite finite systems

A. Vourdas and S. Zhang
A quantum system composed of p1 subsystems, each of which is described with a p-dimensional Hilbert space (where p is a prime number), is considered. A quantum number theoretic transform on this system, which has properties similar to those of a Fourier transform, is studied. A representation of the ... [J. Opt. Soc. Am. A 26, 1360 (2009)] published Mon Jun 15, 2009.

Coherency of su(1,1)-BarutGirardello type and entanglement for spherical harmonics

H. Fakhri and A. Dehghani
BarutGirardello coherent states corresponding to the (lm)- and (l+m)-integer discrete irreducible representations of su(1,1) Lie algebra are calculated by the spherical harmonics Y(theta,phi). Their explicit compact forms and also, to realize the resolution of the identity, their corresponding posit ... [J. Math. Phys. 50, 052104 (2009)] published Wed May 20, 2009.

Heralded quantum memory for single-photon polarization qubits

G. Lin, X. Zou, X. Lin, and G. Guo
We propose a scheme to implement a heralded quantum memory for single-photon polarization qubits with a single atom trapped in an optical cavity. In this scheme, an injected photon only exchanges quantum state with the atom, so that the heralded storage can be achieved by detecting the output photon ... [EPL 86, 30006 (2009)] published Tue May 26, 2009.

Experimentally testable geometric phase of sequences of Everett's relative quantum states

E. Sjoqvist
Everett's concept of relative state is used to introduce a geometric phase that depends nontrivially on entanglement in a pure quantum state. We show that this phase can be measured in multiparticle interferometry. A correlation-dependent generalization of the relative state geometric phase to mixed ... [EPL 86, 30005 (2009)] published Tue May 26, 2009.

Single-mode operation of a high-brightness narrow-band single-photon source

M. Scholz, L. Koch, R. Ullmann, and O. Benson
We demonstrate a narrow-band single-photon source based on cavity-enhanced parametric downconversion for efficient coupling to atomic quantum memories. Selecting a single longitudinal cavity mode by spectral filtering, we achieve a spectral brightness of ~330 biphotons/(s mW MHz) and an overall ban ... [Appl. Phys. Lett. 94, 201105 (2009)] published Tue May 19, 2009.

Economical (k,m)-threshold controlled quantum teleportation

Akira SaiToh, Robabeh Rahimi, and Mikio Nakahara
We study a (k,m)-threshold controlling scheme for controlled quantum teleportation. A standard polynomial coding over GF(p) with prime p>m1 needs to distribute a d-dimensional qudit with d>=p to each controller for this purpose. We propose a scheme using m qubits (two-dimensional qudits) for the con ... [Phys. Rev. A 79, 062313 (2009)] published Mon Jun 15, 2009.

Observation of a large-gap topological-insulator class with a single Dirac cone on the surface

Y. Xia, D. Qian, D. Hsieh, L. Wray, A. Pal et al.
Recent experiments and theories have suggested that strong spinorbit coupling effects in certain band insulators can give rise to a new phase of quantum matter, the so-called topological insulator, which can show macroscopic quantum-entanglement effects. Such systems feature two-dimensional surface ... [Nature Phys. 5, 398 (2009)] published Wed Jun 3, 2009.

Near-zero modes in condensate phases of the Dirac theory on the honeycomb lattice

Doron L. Bergman and Karyn Le Hur
We investigate a number of fermionic condensate phases on the honeycomb lattice to determine whether topological defects (vortices and edges) in these phases can support bound states with zero energy. We argue that topological zero modes bound to vortices and at edges are not only connected, but sho ... [Phys. Rev. B 79, 184520 (2009)] published Fri May 22, 2009.

Erratum: Security of coherent-state quantum cryptography in the presence of Gaussian noise [Phys. Rev. A 76, 022313 (2007)]

Matthias Heid and Norbert Lutkenhaus
Abstract not available. [Phys. Rev. A 79, 059902 (2009)] published Mon May 18, 2009.

Distinguishability of Gaussian states in quantum cryptography using postselection

Christian Weedbrook, Daniel J. Alton, Thomas Symul, Ping Koy Lam, and Timothy C. Ralph
We consider the distinguishability of Gaussian states from the viewpoint of continuous-variable quantum cryptography using postselection. Specifically, we use the probability of error to distinguish between two pure coherent (squeezed) and two particular mixed symmetric coherent (squeezed) states wh ... [Phys. Rev. A 79, 062311 (2009)] published Mon Jun 15, 2009.

Decoy-state theory for the heralded single-photon source with intensity fluctuations

Shuang Wang, Sheng-Li Zhang, Hong-Wei Li, Zhen-Qiang Yin, Yi-Bo Zhao et al.
The secure key rates of decoy-state quantum key distribution (QKD) using the heralded single-photon source (HSPS) are recalculated in the case of intensity fluctuations. By numerical simulations, we show that the HSPS is a good source for decoy-state QKD experiments not only because it has larger up ... [Phys. Rev. A 79, 062309 (2009)] published Wed Jun 10, 2009.

Enhanced single-photon emission in the near infrared from a diamond color center

Igor Aharonovich, Chunyuan Zhou, Alastair Stacey, Julius Orwa, Stefania Castelletto et al.
Individual color centers in diamond are promising for near-term quantum technologies including quantum key distribution and metrology. Here we show fabrication of an as-yet uncharacterized nickel-related complex in diamond which has photophysical properties surpassing the two main-stay centers for s ... [Phys. Rev. B 79, 235316 (2009)] published Mon Jun 15, 2009.

Multiple-image optical encryption: an improved encoding approach

Xiao Yong-Liang, Zhou Xin, Yuan Sheng, Liu Qiang, and Li Yang-Cong
An improved encoding approach to multiple-image optical encryption based on a cascaded phase retrieval algorithm (CPRA) is proposed. The system consists of several stages of a standard 4-f correlator, in which the keys are not only the phase mask pairs produced by CPRA but also the phase distributio ... [Appl. Opt. 48, 2686 (2009)] published Mon May 18, 2009.

Fast time-domain balanced homodyne detection of light

Ondrej Haderka, Vaclav Michalek, Vladimir Urbasek, and Miroslav Jezek
A balanced homodyne detection scheme with nanosecond time resolution and sub-shot-noise sensitivity has been developed and successfully tested yielding an efficient detection scheme for high-speed quantum-optical measurements and communication protocols, for example, quantum cryptography. The parame ... [Appl. Opt. 48, 2884 (2009)] published Wed Jun 3, 2009.

Ultrashort dead time of photon-counting InGaAs avalanche photodiodes

A. R. Dixon, J. F. Dynes, Z. L. Yuan (袁之良), A. W. Sharpe, A. J. Bennett et al.
We report a 1.036 GHz gated Geiger mode InGaAs avalanche photodiode with a detection dead time of just 1.93 ns. This is demonstrated by full recovery of the detection efficiency two gate cycles after a detection event, as well as a measured maximum detection rate of 497 MHz. As an application, we me ... [Appl. Phys. Lett. 94, 231113 (2009)] published Tue Jun 9, 2009.

Standardization of quantum key distribution and the ETSI standardization initiative ISG-QKD

Thomas Langer and Gaby Lenhart
In recent years, quantum key distribution (QKD) has been the object of intensive research activities and of rapid progress, and it is now developing into a competitive industry with commercial products. Once QKD systems are transferred from the controlled environment of physical laboratories into a ... [New J. Phys. 11, 055051 (2009)] published Wed Jun 3, 2009.

1.5 GHz single-photon detection at telecommunication wavelengths using sinusoidally gated InGaAs/InP avalanche photodiode

Naoto Namekata, Shunsuke Adachi, and Shuichiro Inoue
We report a telecom-band single-photon detector for gigahertz clocked quantum key distribution systems. The single-photon detector is based on a sinusoidally gated InGaAs/InP avalanche photodiode. The gate repetition frequency of the single-photon detector reached 1.5 GHz. A quantum efficiency of 10 ... [Opt. Express 17, 6275 (2009)] published Mon May 18, 2009.

Photon nonlinear mixing in subcarrier multiplexed quantum key distribution systems

Jose Capmany
We provide, for the first time to our knowledge, an analysis of the influence of nonlinear photon mixing on the end to end quantum bit error rate (QBER) performance of subcarrier multiplexed quantum key distribution systems. The results show that negligible impact is to be expected for modulation in ... [Opt. Express 17, 6457 (2009)] published Mon May 18, 2009.

Field test of a practical secure communication network with decoy-state quantum cryptography

Teng-Yun Chen, Hao Liang, Yang Liu, Wen-Qi Cai, Lei Ju et al.
We present a secure network communication system that operated with decoy-state quantum cryptography in a real-world application scenario. The full key exchange and application protocols were performed in real time among three nodes, in which two adjacent nodes were connected by approximate 20 km of ... [Opt. Express 17, 6540 (2009)] published Mon May 18, 2009.

Polarization-independent, differential-phase-shift, quantum-key distribution system using upconversion detectors

Yuki Iwai, Toshimori Honjo, Kyo Inoue, Hidehiko Kamada, Yoshiki Nishida et al.
We propose and demonstrate a polarization-independent, differential-phase-shift, quantum-key distribution system with upconversion detectors. Even though the detectors have polarization dependency, use of alternative polarization modulation and a two-bit delay interferometer achieves polarization-in ... [Opt. Lett. 34, 1606 (2009)] published Thu May 28, 2009.

Arbitrated quantum signature scheme using Bell states

Qin Li, W. H. Chan, and Dong-Yang Long
In an arbitrated quantum signature scheme, the signatory signs the message and the receiver verifies the signature's validity with the assistance of the arbitrator. We present an arbitrated quantum signature scheme using two-particle entangled Bell states similar to the previous scheme using three-p ... [Phys. Rev. A 79, 054307 (2009)] published Thu May 21, 2009.

Narrowband high-fidelity all-fibre source of heralded single photons at 1570 nm

A. R. McMillan, J. Fulconis, M. Halder, C. Xiong, J. G. Rarity et al.
An all-fibre heralded single photon source operating at 1570 nm has been demonstrated. The device generates correlated photon pairs, widely spaced in frequency, through four-wave mixing in a photonic crystal fibre. Separation of the pair photons and narrowband filtering is all achieved in fibre. The ... [Opt. Express 17, 6156 (2009)] published Mon May 18, 2009.

Preparation of many-body states for quantum simulation

Nicholas J. Ward, Ivan Kassal, and Alan Aspuru-Guzik
While quantum computers are capable of simulating many quantum systems efficiently, the simulation algorithms must begin with the preparation of an appropriate initial state. We present a method for generating physically relevant quantum states on a lattice in real space. In particular, the present ... [J. Chem. Phys. 130, 194105 (2009)] published Mon May 18, 2009.

Efficient quantum circuit implementation of quantum walks

B. L. Douglas and J. B. Wang
Quantum walks, being the quantum analog of classical random walks, are expected to provide a fruitful source of quantum algorithms. A few such algorithms have already been developed, including the glued trees algorithm, which provides an exponential speedup over classical methods, relative to a part ... [Phys. Rev. A 79, 052335 (2009)] published Wed May 27, 2009.

Gapped Two-Body Hamiltonian Whose Unique Ground State Is Universal for One-Way Quantum Computation

Xie Chen, Bei Zeng, Zheng-Cheng Gu, Beni Yoshida, and Isaac L. Chuang
Many-body entangled quantum states studied in condensed matter physics can be primary resources for quantum information, allowing any quantum computation to be realized using measurements alone, on the state. Such a universal state would be remarkably valuable, if only it were thermodynamically stab ... [Phys. Rev. Lett. 102, 220501 (2009)] published Fri Jun 5, 2009.

Light-cone matrix product

M. B. Hastings
We show how to combine the light-cone and matrix product algorithms to simulate quantum systems far from equilibrium for long times. For the case of the XXZ spin chain at Delta=0.5, we simulate to a time of [approximate]22.5. While part of the long simulation time is due to the use of the light-cone ... [J. Math. Phys. 50, 095207 (2009)] published Thu Jun 11, 2009.

Classical diffusion of a quantum particle in a noisy environment

Ariel Amir, Yoav Lahini, and Hagai B. Perets
We study the spreading of a quantum-mechanical wave packet in a tight-binding model with a noisy potential and analyze the emergence of classical diffusion from the quantum dynamics due to decoherence. We consider a finite correlation time of the noisy environment and treat the system by utilizing t ... [Phys. Rev. E 79, 050105 (2009)] published Fri May 22, 2009.

Local controllability of quantum networks

Daniel Burgarth, Sougato Bose, Christoph Bruder, and Vittorio Giovannetti
We give a sufficient criterion that guarantees that a many-body quantum system can be controlled by properly manipulating the (local) Hamiltonian of one of its subsystems. The method can be applied to a wide range of systems: it does not depend on the details of the couplings but only on their assoc ... [Phys. Rev. A 79, 060305 (2009)] published Mon Jun 15, 2009.

Construction of a universal quantum computer

Antonio A. Lagana, M. A. Lohe, and Lorenz von Smekal
We construct a universal quantum computer following Deutsch's original proposal of a universal quantum Turing machine (UQTM). Like Deutsch's UQTM, our machine can emulate any classical Turing machine and can execute any algorithm that can be implemented in the quantum gate array framework but under ... [Phys. Rev. A 79, 052322 (2009)] published Mon May 18, 2009.

Quantum computation of multifractal exponents through the quantum wavelet transform

Ignacio Garcia-Mata, Olivier Giraud, and Bertrand Georgeot
We study the use of the quantum wavelet transform to extract efficiently information about the multifractal exponents for multifractal quantum states. We show that, combined with quantum simulation algorithms, it enables to build quantum algorithms for multifractal exponents with a polynomial gain c ... [Phys. Rev. A 79, 052321 (2009)] published Mon May 18, 2009.

Simulations of quantum double models

G Brennen, M Aguado, and J Cirac
We demonstrate how to build a simulation of two-dimensional (2D) physical theories describing topologically ordered systems whose excitations are in one-to-one correspondence with irreducible representations of a Hopf algebra, D(G), the quantum double of a finite group G. Our simulation uses a digit ... [New J. Phys. 11, 053009 (2009)] published Wed Jun 3, 2009.

Consistency of the Adiabatic Theorem

M. H. S. Amin
The adiabatic theorem provides the basis for the adiabatic model of quantum computation. Recently the conditions required for the adiabatic theorem to hold have become a subject of some controversy. Here we show that the reported violations of the adiabatic theorem all arise from resonant transition ... [Phys. Rev. Lett. 102, 220401 (2009)] published Wed Jun 3, 2009.

A fast and efficient algorithm for Slater determinant updates in quantum Monte Carlo simulations

Phani K. V. V. Nukala and P. R. C. Kent
We present an efficient low-rank updating algorithm for updating the trial wave functions used in quantum Monte Carlo (QMC) simulations. The algorithm is based on low-rank updating of the Slater determinants. In particular, the computational complexity of the algorithm is [script O](kN) during the k ... [J. Chem. Phys. 130, 204105 (2009)] published Thu May 28, 2009.

Density functional theory and quantum computation

Frank Gaitan and Franco Nori
This paper establishes the applicability of density functional theory methods to quantum computing systems. We show that ground state and time-dependent density functional theory can be applied to quantum computing systems by proving the Hohenberg-Kohn and Runge-Gross theorems for a fermionic repres ... [Phys. Rev. B 79, 205117 (2009)] published Tue May 26, 2009.