Virtual Journal of Quantum Information

Tuning micropillar cavity birefringence by laser induced surface defects

Cristian Bonato, Dapeng Ding, Jan Gudat, Susanna Thon, Hyochul Kim et al.
We demonstrate a technique to tune the optical properties of micropillar cavities by creating small defects on the sample surface near the cavity region with an intense focused laser beam. Such defects modify strain in the structure, changing the birefringence in a controllable way. We apply the tec ... [Appl. Phys. Lett. 95, 251104 (2009)] published Tue Dec 22, 2009.

Producing optimized ensembles of nitrogen-vacancy color centers for quantum information applications

Igor Aharonovich, Charles Santori, Barbara A. Fairchild, Julius Orwa, Kumaravelu Ganesan et al.
Quantum information applications place stringent demands on the development of platforms that can host them. Color centers in diamond have been identified as important media for quantum information processing. Accordingly, the photoluminescence properties of nitrogen-vacancy (N-V) centers in diamond ... [J. Appl. Phys. 106, 124904 (2009)] published Mon Dec 21, 2009.

Hole-spin mixing in InAs quantum dot molecules

M. F. Doty, J. I. Climente, A. Greilich, M. Yakes, A. S. Bracker et al.
The spin state of holes confined in single InAs quantum dots have recently emerged as a promising system for the storage or manipulation of quantum information. These holes are often assumed to have no mixing between orthogonal heavy-hole-spin projections (in the absence of a transverse magnetic fie ... [Phys. Rev. B 81, 035308 ] published .

Efficient all-optical routing using dynamically induced transparency windows and photonic band gaps

Jin-Wei Gao, Jin-Hui Wu, Nuo Ba, Cui-Li Cui, and Xing-Xia Tian
By investigating the steady optical response of a cold atomic ensemble, we find that one high-reflection band gap and one high-transmission region with comparable widths may be dynamically induced and well controlled around the probe resonance by a traveling-wave coupling field and a standing-wave g ... [Phys. Rev. A 81, 013804 ] published .

Synchronization of multiple coupled rf-SQUID flux qubits

R Harris, F Brito, A Berkley, J Johansson, M Johnson et al.
A practical strategy for synchronizing the properties of compound Josephson junction (CJJ) radio frequency monitored superconducting quantum interference device (rf-SQUID) qubits on a multi-qubit chip has been demonstrated. The impact of small (~1%) fabrication variations in qubit inductance and cri ... [New J. Phys. 11, 123022 (2009)] published Wed Dec 30, 2009.

Cooling down quantum bits on ultrashort time scales

Goren Gordon, Guy Bensky, David Gelbwaser-Klimovsky, D Bhaktavatsala Rao, Noam Erez et al.
Quantum two-state systems, known as quantum bits (qubits), are unavoidably in contact with their uncontrolled thermal environment, also known as a macroscopic `bath'. The higher the temperature of the qubits, the more impure their quantum state and the less useful they are for coherent control or qu ... [New J. Phys. 11, 123025 (2009)] published Wed Dec 30, 2009.

Speed of Markovian relaxation toward the ground state

Malte Vogl, Gernot Schaller, and Tobias Brandes
For sufficiently low reservoir temperatures, it is known that open quantum systems subject to decoherent interactions with the reservoir relax toward their ground state in the weak coupling limit. Within the framework of quantum master equations, this is formalized by the Born-Markov-secular (BMS) a ... [Phys. Rev. A 81, 012102 ] published .

Manipulation of Nonclassical Atomic Spin States

Tetsushi Takano, Shin-Ichi-Ro Tanaka, Ryo Namiki, and Yoshiro Takahashi
We report successful manipulation of nonclassical atomic spin states. We apply an off-resonant noncircularly-polarized light pulse to a measurement-induced squeezed spin state of a cold atomic ensemble. By changing the pulse duration, we clearly observe a rotation of the anisotropic quantum-noise di ... [Phys. Rev. Lett. 104, 013602 ] published .

Josephson phase qubit with an optimal point

Norihito Kosugi, Shigemasa Matsuo, Toshiyuki Fujii, and Noriyuki Hatakenaka
Current fluctuations in a Josephson phase qubit are considered to be a source of decoherence, especially for pure dephasing. One possible way of evading such decoherence is to employ an optimal operation point as used in flux and charge qubits, where the qubit is insensitive to the bias fluctuations ... [Phys. Rev. B 81, 024507 ] published .

Identification of individual C isotopes of nitrogen-vacancy center in diamond by combining the polarization studies of nuclear spins and first-principles calculations

Adam Gali
We determine the charge- and spin-density distributions of nitrogen-vacancy center in diamond for both the ground and excited states by ab initio supercell calculations yielding very good agreement with the experiment. We correctly determine the polarization of N nuclear spin in the level anticrossi ... [Phys. Rev. B 80, 241204 ] published .

Valence holes as Luttinger spinor based qubits in quantum dots

Chang-Yu Hsieh, Ross Cheriton, Marek Korkusinski, and Pawel Hawrylak
We present a theory of valence holes as Luttinger spinor based qubits in p-doped self-assembled quantum dots within the four-band kp formalism. The two-qubit levels are identified with the two chiralities of the doubly degenerate ground state. We show that single-qubit operations can be implemented ... [Phys. Rev. B 80, 235320 (2009)] published Wed Dec 16, 2009.

Polarization control of single photon quantum orbital angular momentum states

E. Nagali, F. Sciarrino, F. De Martini, B. Piccirillo, E. Karimi et al.
The orbital angular momentum of photons, being defined in an infinite-dimensional discrete Hilbert space, offers a promising resource for high-dimensional quantum information protocols in quantum optics. The biggest obstacle to its wider use is presently represented by the limited set of tools avail ... [Opt. Express 17, 18745 (2009)] published Tue Dec 29, 2009.

Rotating single atoms in a ring lattice generated by a spatial light modulator

Xiaodong He, Peng Xu, Jin Wang, and Mingsheng Zhan
We demonstrated trapping single neutral Rb atoms in microtraps of an optical ring lattice formed by superposing the l componentsof the Laguerre-Gaussian mode, and generated by reflecting a single laserbeam from a computer controlled spatial light modulator. A single atomin one trap or two atoms with ... [Opt. Express 17, 21007 (2009)] published Tue Dec 29, 2009.

Metastable Superconducting Qubit

Andrew J. Kerman
We propose a superconducting qubit design, based on a tunable rf SQUID and nanowire kinetic inductors, which has a dramatically reduced transverse electromagnetic coupling to its environment, so that its excited state should be metastable. If electromagnetic interactions are in fact responsible for ... [Phys. Rev. Lett. 104, 027002 ] published .

Quantum interface between light and nuclear spins in quantum dots

Heike Schwager, J. Ignacio Cirac, and Gza Giedke
The coherent coupling of flying photonic qubits to stationary matter-based qubits is an essential building block for quantum-communication networks. We show how such a quantum interface can be realized between a traveling-wave optical field and the polarized nuclear spins in a singly charged quantum ... [Phys. Rev. B 81, 045309 ] published .

Inhomogeneous nuclear spin flips: Feedback mechanism between electronic states in a double quantum dot and the underlying nuclear spin bath

M. Stopa, J. J. Krich, and A. Yacoby
We discuss a feedback mechanism between electronic states in a two-electron double quantum dot and the underlying nuclear spin bath. We analyze two pumping cycles for which this feedback provides a force for the Overhauser fields of the two dots to either equilibrate or diverge. Which of these effec ... [Phys. Rev. B 81, 041304 ] published .

Interferometry using spatial adiabatic passage in quantum dot networks

Lenneke M. Jong and Andrew D. Greentree
We show that techniques of spatial adiabatic passage can be used to realize an electron interferometer in a geometry analogous to a conventional Aharonov-Bohm ring, with transport of the particle through the device modulated using coherent transport adiabatic passage. This device shows an interestin ... [Phys. Rev. B 81, 035311 ] published .

Fundamental gates for a strongly correlated two-electron quantum ring

L. Slen, E. Waltersson, J. P. Hansen, and E. Lindroth
We demonstrate that conditional as well as unconditional basic operations which are necessary for universal quantum gates can be performed with almost 100% fidelity within a strongly interacting two-electron quantum ring. Both sets of operations are based on a quantum control algorithm that optimize ... [Phys. Rev. B 81, 033303 ] published .

Vortex qubit based on an annular Josephson junction containing a microshort

A. N. Price, A. Kemp, D. R. Gulevich, F. V. Kusmartsev, and A. V. Ustinov
We report theoretical and experimental work on the development of a vortex qubit based on a microshort in an annular Josephson junction. The microshort creates a potential barrier for the vortex, which produces a double-well potential under the application of an in-plane magnetic field; the field st ... [Phys. Rev. B 81, 014506 ] published .

Pulse imaging and nonadiabatic control of solid-state artificial atoms

Jonas Bylander, Mark S. Rudner, Andrey V. Shytov, Sergio O. Valenzuela, David M. Berns et al.
Transitions in an artificial atom, driven nonadiabatically through an energy-level avoided crossing, can be controlled by carefully engineering the driving protocol. We have driven a superconducting persistent-current qubit with a large-amplitude radio-frequency field. By applying a biharmonic wave ... [Phys. Rev. B 80, 220506 (2009)] published Wed Dec 23, 2009.

Current fluctuations in rough superconducting tunnel junctions

Georg Heinrich and F. K. Wilhelm
Intrinsic noise is known to be ubiquitous in Josephson junctions. We introduce a rough tunnel junction model characterized by a very small number of pinholestransport channels possessing a transmission coefficient close to unity and analyze its transport properties. Although it may still have just a ... [Phys. Rev. B 80, 214536 (2009)] published Wed Dec 30, 2009.

Weak-coupling study of decoherence of a qubit in disordered magnetic environments

E. A. Winograd, M. J. Rozenberg, and R. Chitra
We study the decoherence of a qubit weakly coupled to frustrated spin baths. We focus on spin baths described by the classical Ising spin glass and the quantum random transverse Ising model which are known to have complex thermodynamic phase diagrams as a function of an external magnetic field and t ... [Phys. Rev. B 80, 214429 (2009)] published Thu Dec 31, 2009.

Noise-induced quantum coherence and persistent Rabi oscillations in a Josephson flux qubit

A. N. Omelyanchouk, S. Savel'ev, A. M. Zagoskin, E. Il'ichev, and Franco Nori
We predict theoretically the enhancement of quantum coherence in a superconducting flux qubit by a classical external noise. First, the off-diagonal components of the qubit density matrix are increased. Second, in the presence of both ac drive and noise, the resulting Rabi oscillations survive in pe ... [Phys. Rev. B 80, 212503 (2009)] published Wed Dec 30, 2009.

Multifrequency control pulses for multilevel superconducting quantum circuits

Anne M. Forney, Steven R. Jackson, and Frederick W. Strauch
Superconducting quantum circuits, such as the superconducting phase qubit, have multiple quantum states that can interfere with ideal qubit operation. The use of multiple frequency control pulses, resonant with the energy differences of the multistate system, is theoretically explored. An analytical ... [Phys. Rev. A 81, 012306 ] published .

Experimental estimation of one-parameter qubit gates in the presence of phase diffusion

Davide Brivio, Simone Cialdi, Stefano Vezzoli, Berihu Teklu Gebrehiwot, Marco G. Genoni et al.
We address estimation of one-parameter qubit gates in the presence of phase diffusion. We evaluate the ultimate quantum limits to precision, seek optimal probes and measurements, and demonstrate an optimal estimation scheme for polarization encoded optical qubits. An adaptive method to achieve optim ... [Phys. Rev. A 81, 012305 ] published .

Band structure, phase transitions, and semiconductor analogs in one-dimensional solid light systems

James Quach, Melissa I. Makin, Chun-Hsu Su, Andrew D. Greentree, and Lloyd C. L. Hollenberg
The conjunction of atom-cavity physics and photonic structures (solid light systems) offers new opportunities in terms of more device functionality and the probing of designed emulators of condensed-matter systems. By analogy to the canonical one-electron approximation of solid-state physics, we pro ... [Phys. Rev. A 80, 063838 (2009)] published Mon Dec 28, 2009.

Quantum computation with graphene nanoribbon

Guo-Ping Guo, Zhi-Rong Lin, Tao Tu, Gang Cao, Xiao-Peng Li et al.
We propose a scheme to implement quantum computation in graphene nanoribbon (GNR). It is shown that an electron or hole can be naturally localized in each zigzag region for a GNR with a sequence of Z-shaped structures, without using confined gates. A one-dimensional graphene quantum dot chain is for ... [New J. Phys. 11, 123005 (2009)] published Wed Dec 30, 2009.

Distributed CNOT gate via quantum Zeno dynamics

Xiao-Qiang Shao, Hong-Fu Wang, Li Chen, Shou Zhang, Yong-Fang Zhao et al.
We show how the quantum Zeno effect can be exploited to implement the CNOT gate in two separated cavities with two atomic four-level tripod systems. In respective subspaces of the total Hilbert space, the evolution of the quantum system exhibits different dynamical properties due to the continuous c ... [J. Opt. Soc. Am. B 26, 2440 (2009)] published Tue Dec 29, 2009.

Quantum gate operations using midinfrared binary shaped pulses on the rovibrational states of carbon monoxide

Ryan R. Zaari and Alex Brown
Frequency domain shaped binary laser pulses were optimized to perform 2 qubit quantum gate operations in CO. The qubit rovibrational state representation was chosen so that all gate operations consisted of one-photon transitions. The amplitude and phase varied binary pulses were determined using a g ... [J. Chem. Phys. 132, 014307 (2010)] published Wed Jan 6, 2010.

Novel Radiation-Induced Magnetoresistance Oscillations in a Nondegenerate Two-Dimensional Electron System on Liquid Helium

Denis Konstantinov and Kimitoshi Kono
We report the observation of novel magnetoresistance oscillations induced by the resonant intersubband absorption in nondegenerate 2D electrons bound to the surface of liquid He. The oscillations are periodic in B and originate from the scattering-mediated transitions of the excited electrons into t ... [Phys. Rev. Lett. 103, 266808 (2009)] published Thu Dec 31, 2009.

Commensurate quantum oscillations in coupled qubits

Mun Dae Kim
We study the coupled-qubit oscillation driven by an oscillating field. When the period of the nonresonant mode is commensurate with that of the resonant mode of the Rabi oscillation, we show that the controlled-NOT (CNOT) gate operation can be demonstrated. For a weak coupling the CNOT gate operatio ... [Phys. Rev. B 81, 014504 ] published .

Superconducting phase qubit based on the Josephson oscillator with strong anharmonicity

A. B. Zorin and F. Chiarello
We propose a superconducting phase qubit on the basis of the radio-frequency superconducting quantum interference device with the screening parameter value beta[equivalent](2pi/Phi)LI[approximate]1, biased by a half-flux quantum Phi=Phi/2. Significant anharmonicity (>30%) can be achieved in this sys ... [Phys. Rev. B 80, 214535 (2009)] published Wed Dec 30, 2009.

Realization of a programmable two-qubit quantum processor

D. Hanneke, J. P. Home, J. D. Jost, J. M. Amini, D. Leibfried et al.
The universal quantum computer is a device capable of simulating any physical system and represents a major goal for the field of quantum information science. In the context of quantum information, `universal' refers to the ability to carry out arbitrary unitary transformations in the system's comp ... [Nature Phys. 6, 13 (2009)] published Tue Dec 29, 2009.

Non-negative Wigner functions for orbital angular momentum states

I. Rigas, L. L. Snchez-Soto, A. B. Klimov, J. ehek, and Z. Hradil
The Wigner function of a pure continuous-variable quantum state is non-negative if and only if the state is Gaussian. Here we show that for the canonical pair angle and angular momentum, the only pure states with non-negative Wigner functions are the eigenstates of the angular momentum. Some implica ... [Phys. Rev. A 81, 012101 ] published .

Optimal Measurement on Noisy Quantum Systems

Yu Watanabe, Takahiro Sagawa, and Masahito Ueda
We identify the optimal measurement for obtaining information about the original quantum state after the state to be measured has undergone partial decoherence due to noise. We quantify the information that can be obtained by the measurement in terms of the Fisher information and find its value for ... [Phys. Rev. Lett. 104, 020401 ] published .

Hermitian conjugate measurement

Hiroaki Terashima and Masahito Ueda
We propose a class of probabilistic reversing operations on the state of a system that was disturbed by a weak measurement. It can approximately recover the original state from the disturbed state especially with an additional information gain using the Hermitian conjugate of the measurement operato ... [Phys. Rev. A 81, 012110 ] published .

Complete characterization of post-selected quantum statistics using weak measurement tomography

Holger F. Hofmann
The reconstruction of quantum states from a sufficient set of experimental data can be achieved with arbitrarily weak measurement interactions. Since such weak measurements have negligible back action, the quantum state reconstruction is also valid for the postselected subensembles usually considere ... [Phys. Rev. A 81, 012103 ] published .

Non-Markovian incoherent quantum dynamics of a two-state system

M. H. S. Amin and Frederico Brito
We present a detailed study of the non-Markovian two-state system dynamics for the regime of incoherent quantum tunneling. Using perturbation theory in the system tunneling amplitude Delta, and in the limit of strong system-bath coupling, we determine the short-time evolution of the reduced density ... [Phys. Rev. B 80, 214302 (2009)] published Fri Dec 18, 2009.

A generalized statistical complexity measure: Applications to quantum systems

R. Lopez-Ruiz, A. Nagy, E. Romera, and J. Sanudo
A two-parameter family of complexity measures C-tilde based on the Renyi entropies is introduced and characterized by a detailed study of its mathematical properties. This family is the generalization of a continuous version of the Lopez-RuizManciniCalbet complexity, which is recovered for alpha=1 a ... [J. Math. Phys. 50, 123528 (2009)] published Thu Dec 31, 2009.

Local Unitary Equivalence of Multipartite Pure States

B. Kraus
Necessary and sufficient conditions for the equivalence of arbitrary n-qubit pure quantum states under local unitary (LU) operations are derived. First, an easily computable standard form for multipartite states is introduced. Two generic states are shown to be LUequivalent iff their standard forms ... [Phys. Rev. Lett. 104, 020504 ] published .

Tensor rank of the tripartite state |W

Nengkun Yu, Eric Chitambar, Cheng Guo, and Runyao Duan
Tensor rank refers to the number of product states needed to express a given multipartite quantum state. Its nonadditivity as an entanglement measure has recently been observed. In this Brief Report, we estimate the tensor rank of multiple copies of the tripartite state |W=(1/(sqrt(3)))(|100+|010+|0 ... [Phys. Rev. A 81, 014301 ] published .

Channel capacities versus entanglement measures in multiparty quantum states

Aditi Sen(De) and Ujjwal Sen
For quantum states of two subsystems, highly entangled states have a higher capacity of transmitting classical as well as quantum information, and vice versa. We show that this is no more the case in general: Quantum capacities of multiaccess channels, motivated by communication in quantum networks, ... [Phys. Rev. A 81, 012308 ] published .

Fair-sampling assumption is not necessary for testing local realism

Dominic W. Berry, Hyunseok Jeong, Magdalena Stobiska, and Timothy C. Ralph
Almost all Bell inequality experiments to date have used postselection and therefore relied on the fair sampling assumption for their interpretation. The standard form of the fair sampling assumption is that the loss is independent of the measurement settings, so the ensemble of detected systems pro ... [Phys. Rev. A 81, 012109 ] published .

Vacuum Degeneracy of a Circuit QED System in the Ultrastrong Coupling Regime

Pierre Nataf and Cristiano Ciuti
We investigate theoretically the quantum vacuum properties of a chain of N superconducting Josephson atoms inductively coupled to a transmission line resonator. We derive the quantum field Hamiltonian for such a circuit QED system, showing that, due to the type and strength of the interaction, a qua ... [Phys. Rev. Lett. 104, 023601 ] published .

Stable topological superconductivity in a family of two-dimensional fermion models

Meng Cheng, Kai Sun, Victor Galitski, and S. Das Sarma
We show that a large class of two-dimensional spinless fermion models exhibit topological superconducting phases characterized by a nonzero Chern number. More specifically, we consider a generic one-band Hamiltonian of spinless fermions that is invariant under both time reversal, [openface T], and a ... [Phys. Rev. B 81, 024504 ] published .

Fighting decoherence in a continuous two-qubit odd- or even-parity measurement with a closed-loop setup

Anne E. B. Nielsen
A parity measurement on two qubits, each consisting of a single atom in a cavity, can be realized by measuring the phase shift of a probe beam which interacts sequentially with the two qubits, but imperfections lead to decoherence within the subspaces of a given parity. We demonstrate that a differe ... [Phys. Rev. A 81, 012307 ] published .

Optimized dynamical decoupling for power-law noise spectra

S. Pasini and G. S. Uhrig
We analyze the suppression of decoherence by means of dynamical decoupling in the pure-dephasing spin-boson model for baths with power law spectra. The sequence of ideal pulses is optimized according to the power of the bath. We expand the decoherence function and separate the canceling divergences ... [Phys. Rev. A 81, 012309 ] published .

Erratum: Three-electron anisotropic quantum dots in variable magnetic fields: Exact results for excitation spectra, spin structures, and entanglement [Phys. Rev. B 76, 245310 (2007)]

Yuesong Li, Constantine Yannouleas, and Uzi Landman
Abstract not available. [Phys. Rev. B 81, 049902 ] published .

The geometric measure of entanglement for a symmetric pure state with non-negative amplitudes

Masahito Hayashi, Damian Markham, Mio Murao, Masaki Owari, and Shashank Virmani
In this paper for a class of symmetric multiparty pure states, we consider a conjecture related to the geometric measure of entanglement: for a symmetric pure state, the closest product state in terms of the fidelity can be chosen as a symmetric product state. We show that this conjecture is true fo ... [J. Math. Phys. 50, 122104 (2009)] published Mon Dec 28, 2009.

Quantum physics meets biology

Markus Arndt, Thomas Juffmann, and Vlatko Vedral
Quantum physics and biology have long been regarded as unrelated disciplines, describing nature at the inanimate microlevel on the one hand and living species on the other hand. Over the past decades the life sciences have succeeded in providing ever more and refined explanations of macroscopic phen ... [HFSP J. 3, 386 (2010)] published Wed Jan 13, 2010.

Graphene armchair nanoribbon single-electron transistors: The peculiar influence of end states

S. Koller, L. Mayrhofer, and M. Grifoni
We present a microscopic theory for interacting graphene armchair nanoribbon quantum dots. Long-range interaction processes are responsible for Coulomb blockade and spin-charge separation. Short-range ones, arising from the underlying honeycomb lattice of graphene smear the spin-charge separation an ... [EPL 88, 57001 (2009)] published Thu Dec 17, 2009.

Energetics of quantum correlations

R. Dillenschneider and E. Lutz
We consider a photo-Carnot engine that consists of a single-mode radiation field in an optical cavity. One the heat reservoirs is made of a beam of thermally entangled pairs of two-level atoms that interact resonantly with the cavity. We express the thermodynamic efficiency of the engine in terms of ... [EPL 88, 50003 (2009)] published Thu Dec 17, 2009.

Entanglement percolation with bipartite mixed states

S. Broadfoot, U. Dorner, and D. Jaksch
We develop a concept of entanglement percolation for long-distance singlet generation in quantum networks with neighboring nodes connected by partially entangled bipartite mixed states. We give a necessary and sufficient condition on the class of mixed network states for the generation of singlets. ... [EPL 88, 50002 (2009)] published Thu Dec 17, 2009.

Quantum entanglement beyond Gaussian criteria

R. M. Gomes, A. Salles, F. Toscano, P. H. Souto Ribeiro, and S. P. Walborn
Most of the attention given to continuous variable systems for quantum information processing has traditionally been focused on Gaussian states. However, non-Gaussianity is an essential requirement for universal quantum computation and entanglement distillation, and can improve the efficiency of ot ... [Proc. Natl. Acad. Sci. U.S.A. 106, 21517 (2009)] published Wed Dec 23, 2009.

Carbon Nanotubes as Cooper-Pair Beam Splitters

L. G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos et al.
We report on conductance measurements in carbon nanotube based double quantum dots connected to two normal electrodes and a central superconducting finger. By operating our devices as beam splitters, we provide evidence for crossed Andreev reflections tunable insitu. This opens an avenue to more sop ... [Phys. Rev. Lett. 104, 026801 ] published .

Nonquantum Entanglement Resolves a Basic Issue in Polarization Optics

B. N. Simon, S. Simon, F. Gori, M. Santarsiero, R. Borghi et al.
The issue raised in this Letter is classical, not only in the sense of being nonquantum, but also in the sense of being quite ancient: which subset of 44 real matrices should be accepted as physical Mueller matrices in polarization optics? Nonquantum entanglement or inseparability between the polari ... [Phys. Rev. Lett. 104, 023901 ] published .

Few-Photon Transport in Low-Dimensional Systems: Interaction-Induced Radiation Trapping

Paolo Longo, Peter Schmitteckert, and Kurt Busch
We present a detailed analysis of the dynamics of photon transport in waveguiding systems in the presence of a two-level system. In these systems, quantum interference effects generate a strong effective optical nonlinearity on the few-photon level. We clarify the relevant physical mechanisms throug ... [Phys. Rev. Lett. 104, 023602 ] published .

Measurement of the Spiral Spectrum of Entangled Two-Photon States

H. Di Lorenzo Pires, H. C. B. Florijn, and M. P. van Exter
We implement an interferometric method to measure the orbital angular momentum (OAM) spectrum of photon pairs generated by spontaneous parametric down-conversion. In contrast with previous experiments, which were all limited by the modal capacity of the detection system, our method operates on the e ... [Phys. Rev. Lett. 104, 020505 ] published .

Teleportation-Induced Correlated Quantum Channels

F. Caruso, V. Giovannetti, and G. M. Palma
Quantum teleportation of an n-qubit state performed using as an entangled resource a general bipartite state of 2n qubits instead of n Bell states is equivalent to a correlated Pauli channel. This yields a new characterization of such channels in terms of many-body correlation functions of the telep ... [Phys. Rev. Lett. 104, 020503 ] published .

Experimental Realization of a Controlled-NOT Gate with Four-Photon Six-Qubit Cluster States

Wei-Bo Gao, Ping Xu, Xing-Can Yao, Otfried Ghne, Adn Cabello et al.
We experimentally demonstrate an optical controlled-NOT (CNOT) gate with arbitrary single inputs based on a 4-photon 6-qubit cluster state entangled both in polarization and spatial modes. We first generate the 6-qubit state, and then, by performing single-qubit measurements, the CNOT gate is applie ... [Phys. Rev. Lett. 104, 020501 ] published .

Demonstration of a Neutral Atom Controlled-NOT Quantum Gate

L. Isenhower, E. Urban, X. L. Zhang, A. T. Gill, T. Henage et al.
We present the first demonstration of a CNOT gate between two individually addressed neutral atoms. Our implementation of the CNOT uses Rydberg blockade interactions between neutral atoms held in optical traps separated by >8m. Using two different gate protocols we measure CNOT fidelities of F=0.73 ... [Phys. Rev. Lett. 104, 010503 ] published .

Entanglement of Two Individual Neutral Atoms Using Rydberg Blockade

T. Wilk, A. Gatan, C. Evellin, J. Wolters, Y. Miroshnychenko et al.
We report the generation of entanglement between two individual Rb atoms in hyperfine ground states |F=1,M=1 and |F=2,M=2 which are held in two optical tweezers separated by 4m. Our scheme relies on the Rydberg blockade effect which prevents the simultaneous excitation of the two atoms to a Rydberg ... [Phys. Rev. Lett. 104, 010502 ] published .

Angular Two-Photon Interference and Angular Two-Qubit States

Anand Kumar Jha, Jonathan Leach, Barry Jack, Sonja Franke-Arnold, Stephen M. Barnett et al.
Using angular-positionorbital-angular-momentum entangled photons, we study angular two-photon interference in a scheme in which entangled photons are made to pass through apertures in the form of double angular slits, and using this scheme, we demonstrate an entangled two-qubit state that is based o ... [Phys. Rev. Lett. 104, 010501 ] published .

Topological Entanglement Renyi Entropy and Reduced Density Matrix Structure

Steven T. Flammia, Alioscia Hamma, Taylor L. Hughes, and Xiao-Gang Wen
We generalize the topological entanglement entropy to a family of topological Renyi entropies parametrized by a parameter alpha, in an attempt to find new invariants for distinguishing topologically ordered phases. We show that, surprisingly, all topological Renyi entropies are the same, independent ... [Phys. Rev. Lett. 103, 261601 (2009)] published Mon Dec 28, 2009.

Discrete Tunable Color Entanglement

S. Ramelow, L. Ratschbacher, A. Fedrizzi, N. K. Langford, and A. Zeilinger
Although frequency multiplexing of information has revolutionized the field of classical communications, the color degree of freedom (DOF) has been used relatively little for quantum applications. We experimentally demonstrate a new hybrid quantum gate that transfers polarization entanglement of non ... [Phys. Rev. Lett. 103, 253601 ] published .

Tomograms of spinning black holes

Chethan Krishnan
The classical internal structure of spinning black holes is vastly different from that of static black holes. We consider spinning Banados-Teitelboim-Zanelli black holes, and probe their interior from the gauge theory. Utilizing the simplicity of the geometry and reverse engineering from the geodesi ... [Phys. Rev. D 80, 126014 (2009)] published Mon Dec 21, 2009.

D3 branes in a Melvin universe: A new realm for gravitational holography

Julian Freed-Brown, Vedika Khemani, and Vatche Sahakian
The decoupling limit of a certain configuration of D3 branes in a Melvin universe defines a sector of string theory known as puff field theory (PFT)a theory with nonlocal dynamics but without gravity. In this work, we present a systematic analysis of the nonlocal states of strongly coupled PFT using ... [Phys. Rev. D 80, 126012 (2009)] published Mon Dec 21, 2009.

Entanglement of a coarse grained quantum field in the expanding universe

Yasusada Nambu and Yuji Ohsumi
We investigate the entanglement of a quantum field in the expanding universe. By introducing a bipartite system using a coarse-grained scalar field, we apply the separability criterion based on the partial transpose operation and numerically calculate the bipartite entanglement between separate spat ... [Phys. Rev. D 80, 124031 (2009)] published Mon Dec 21, 2009.

Quantum teleportation of electrons in quantum wires with surface acoustic waves

Fabrizio Buscemi, Paolo Bordone, and Andrea Bertoni
We propose and numerically simulate a semiconductor device based on coupled quantum wires, suitable for deterministic quantum teleportation of electrons trapped in the minima of surface acoustic waves. We exploit a network of interacting semiconductor quantum wires able to provide the universal set ... [Phys. Rev. B 81, 045312 ] published .

Decoherence of spin qubits due to a nearby charge fluctuator in gate-defined double dots

Guy Ramon and Xuedong Hu
The effects of a nearby two-level charge fluctuator on a double-dot two-spin qubit are studied theoretically. Assuming no direct tunneling between the charge fluctuator and the qubit quantum dots, the Coulomb couplings between the qubit orbital states and the fluctuator are calculated within the Hun ... [Phys. Rev. B 81, 045304 ] published .

Enhanced two-photon processes in single quantum dots inside photonic crystal nanocavities

Ziliang Lin and Jelena Vukovi
We show that the two-photon transition rates of quantum dots coupled to nanocavities are enhanced by up to several orders of magnitude relative to quantum dots in bulk host. We then propose how to take advantage of this enhancement to implement coherent quantum-dot excitation by two-photon absorptio ... [Phys. Rev. B 81, 035301 ] published .

Entanglement generation through an open quantum dot: Exact two-electron scattering state in the Anderson model

Takashi Imamura, Akinori Nishino, and Naomichi Hatano
We analytically study entanglement generation through an open quantum-dot system described by the two-lead Anderson model. We exactly obtain the transition rate between the nonentangled incident state in one lead and the outgoing spin-singlet state in the other lead. We find that only the spin-singl ... [Phys. Rev. B 80, 245323 ] published .

Optically pumping hole spins in coupled quantum dot molecules into a steady state of high concurrence entanglement

Song Yang, Ming Gong, ChuanFeng Li, XuBo Zou, and GuangCan Guo
We present a way to prepare a high concurrence steady state entanglement of two hole spins in a quantum dot molecule. We show that the spontaneous dissipation can be used to induce and stabilize the entanglement with rapid rate. By optical pumping of trion levels, two-qubit singlet state can be auto ... [Phys. Rev. B 80, 235322 (2009)] published Wed Dec 16, 2009.

Simulation of two-dimensional quantum systems using a tree tensor network that exploits the entropic area law

L. Tagliacozzo, G. Evenbly, and G. Vidal
This work explores the use of a tree tensor network ansatz to simulate the ground state of a local Hamiltonian on a two-dimensional lattice. By exploiting the entropic area law, the tree tensor network ansatz seems to produce quasiexact results in systems with sizes well beyond the reach of exact di ... [Phys. Rev. B 80, 235127 (2009)] published Fri Dec 18, 2009.

Entangling two superconducting LC coherent modes via a superconducting flux qubit

Mei-Yu Chen, Matisse W. Y. Tu, and Wei-Min Zhang
Based on a pure solid-state device consisting of two superconducting LC circuits coupled to a superconducting flux qubit, we propose in this paper that the maximally entangled coherent states of the two LC modes can be generated for arbitrary coherent states through flux qubit controls. ... [Phys. Rev. B 80, 214538 (2009)] published Thu Dec 31, 2009.

Critical behavior and entanglement of the random transverse-field Ising model between one and two dimensions

Istvan A. Kovacs and Ferenc Igloi
We consider disordered ladders of the transverse-field Ising model and study their critical properties and entanglement entropy for varying width, w<=20, by numerical application of the strong disorder renormalization group method. We demonstrate that the critical properties of the ladders for any f ... [Phys. Rev. B 80, 214416 (2009)] published Thu Dec 17, 2009.

Approximations for the interparticle interaction energy in an exactly solvable two-electron model atom

I. Nagy and J. Pipek
The capability of different ansatz kernels, denoted as K(r,r), in the calculation of the electron-electron interaction energy is investigated here for an exactly solvable two-electron model atom proposed by Moshinsky. The model atom is in the spin-compensated, paramagnetic ground state. The exact ex ... [Phys. Rev. A 81, 014501 ] published .

Non-Markovian effect on the quantum discord

Bo Wang, Zhen-Yu Xu, Ze-Qian Chen, and Mang Feng
We study the non-Markovian effect on the dynamics of the quantum discord by exactly solving a model consisting of two independent qubits subject to two zero-temperature non-Markovian reservoirs, respectively. Considering the two qubits initially prepared in Bell-like or extended Werner-like states, ... [Phys. Rev. A 81, 014101 ] published .

Fidelity threshold for long-range entanglement in quantum networks

Sbastien Perseguers
We present a strategy to generate long-range entanglement in noisy quantum networks. We consider a cubic lattice whose bonds are partially entangled mixed states of two qubits, and where quantum operations can be applied perfectly at the nodes. In contrast to protocols designed for one- or two-dimen ... [Phys. Rev. A 81, 012310 ] published .

Information-transferring ability of the different phases of a finite XXZ spin chain

Abolfazl Bayat and Sougato Bose
We study the transmission of both classical and quantum information through all the phases of a finite XXZ spin chain. This characterizes the merit of the different phases in terms of their ability to act as a quantum wire. As far as quantum information is concerned, we need only consider the transm ... [Phys. Rev. A 81, 012304 ] published .

Generic two-qubit photonic gates implemented by number-resolving photodetection

Dmitry B. Uskov, A. Matthew Smith, and Lev Kaplan
We combine numerical optimization techniques [Uskov et al., Phys. Rev. A 79, 042326 (2009)] with symmetries of the Weyl chamber to obtain optimal implementations of generic linear-optical Knill-Laflamme-Milburn-type two-qubit entangling gates. We find that while any two-qubit controlled-U gate, incl ... [Phys. Rev. A 81, 012303 ] published .

Witnessing entanglement in phase space using inefficient detectors

Seung-Woo Lee, Hyunseok Jeong, and Dieter Jaksch
We propose a scheme for witnessing entanglement in phase space by significantly inefficient detectors. The implementation of this scheme does not require any additional process for correcting errors, in contrast to previous proposals. Moreover, it allows us to detect entanglement without full a prio ... [Phys. Rev. A 81, 012302 ] published .

Nonclassical photon streams using rephased amplified spontaneous emission

Patrick M. Ledingham, William R. Naylor, Jevon J. Longdell, Sarah E. Beavan, and Matthew J. Sellars
We present a fully quantum mechanical treatment of optically rephased photon echoes. These echoes exhibit noise due to amplified spontaneous emission; however, this noise can be seen as a consequence of the entanglement between the atoms and the output light. With a rephasing pulse one can get an ec ... [Phys. Rev. A 81, 012301 ] published .

Entangling two unequal atoms through a common bath

F. Benatti, R. Floreanini, and U. Marzolino
The evolution of two, noninteracting, two-level atoms immersed in a weakly coupled bath can be described by a refined, time-coarse-grained Markovian evolution, still preserving complete positivity. We find that this improved, reduced dynamics is able to entangle the two atoms even when their interna ... [Phys. Rev. A 81, 012105 ] published .

Resonant interaction of a single atom with single photons from a down-conversion source

C. Schuck, F. Rohde, N. Piro, M. Almendros, J. Huwer et al.
We observe the interaction of a single trapped calcium ion with single photons produced by a narrow-band, resonant down-conversion source [A. Haase et al., Opt. Lett. 34, 55 (2009)], employing a quantum jump scheme. Using the temperature dependence of the down-conversion spectrum and the tunability ... [Phys. Rev. A 81, 011802 ] published .

Statistical properties of light from optical parametric oscillators

Reeta Vyas and Surendra Singh
Coherence properties of light beams generated by optical parametric oscillators (OPOs) are discussed in the region of threshold. Analytic expressions, that are valid throughout the threshold region, for experimentally measurable quantities such as the mean and variance of photon number fluctuations, ... [Phys. Rev. A 80, 063836 (2009)] published Wed Dec 16, 2009.

Protocol for hybrid entanglement between a trapped atom and a quantum dot

Edo Waks and C. Monroe
We propose a quantum optical interface between an atomic and solid-state system. We show that quantum states in a single trapped atom can be entangled with the states of a semiconductor quantum dot through their common interaction with a classical laser field. The interference and detection of the r ... [Phys. Rev. A 80, 062330 (2009)] published Wed Dec 30, 2009.

Distribution of interference in the presence of decoherence

Ludovic Arnaud and Daniel Braun
We study the statistics of quantum interference for completely positive maps. We calculate analytically the mean interference and its second moment for finite-dimensional quantum systems interacting with a simple environment consisting of one or several spins (qudits). The joint propagation of the e ... [Phys. Rev. A 80, 062329 (2009)] published Tue Dec 22, 2009.

Laser-induced electron diffraction in H with linear and circular polarization ultrashort XUV laser pulses

Kai-Jun Yuan, HuiZhong Lu, and Andre D. Bandrauk
Numerical solution of the time-dependent Schrodinger equation for a two-dimension model of H ionization by intense ultrashort (few cycles) extreme ultraviolet (XUV) laser pulses are presented to compare linear and circular polarization angular distributions for aligned molecules. Both ground (X Sigm ... [Phys. Rev. A 80, 061403 (2009)] published Thu Dec 17, 2009.

Time gating of heralded single photons for atomic memories

B. Melholt Nielsen, J. S. Neergaard-Nielsen, and E. S. Polzik
We demonstrate a method for time gating the standard heralded cw spontaneous parametric downconverted single-photon source by using pulsed pumping of an optical parametric oscillator below threshold. The narrow bandwidth, high purity, high spectral brightness, and pseudodeterministic character make ... [Opt. Lett. 34, 3872 (2010)] published Tue Jan 5, 2010.

Mode expansion and Bragg filtering for a high-fidelity fiber-based photon-pair Source

Alexander Ling, Jun Chen, Jingyun Fan, and Alan Migdall
We report the development of a fiber-based single spatial-mode source of photon-pairs where the efficiency of extracting photon-pairs is increased through the use of fiber-end expansion and Bragg filters. This improvement in efficiency enabled a spectrally bright and pure photon-pair source having a ... [Opt. Express 17, 21302 (2009)] published Tue Dec 29, 2009.

Photon energy entanglement characterization by electronic transition interference

Alex Hayat, Pavel Ginzburg, and Meir Orenstein
We propose photon energy qubits and schemes for photon energy entanglement characterization. Bell inequality violation for energy qubits and complete Bell state analysis are demonstrated theoretically. Photon energy superposition state detection is performed by a two-photon absorption interferometer ... [Opt. Express 17, 21280 (2009)] published Tue Dec 29, 2009.

Three-photon N00N states generated by photon subtraction from double photon pairs

Heonoh Kim, Hee Su Park, and Sang-Kyung Choi
We describe an experimental demonstration of a novel three-photon N00N state generation scheme using a single source of photons based on spontaneous parametric down-conversion (SPDC). The three-photon entangled state is generated when a photon is subtracted from a double pair of photons and detected ... [Opt. Express 17, 19720 (2009)] published Tue Dec 29, 2009.

Nonlocal dispersion cancellation using entangled photons

So-Young Baek, Young-Wook Cho, and Yoon-Ho Kim
A pair of optical pulses traveling through two dispersive media will become broadened and, as a result, the degree of coincidence between the optical pulses will be reduced. For a pair of entangled photons, however, nonlocal dispersion cancellation in which the dispersion experienced by one photon c ... [Opt. Express 17, 19241 (2009)] published Tue Dec 29, 2009.

Optimizing type-I polarization-entangled photons

Radhika Rangarajan, Michael Goggin, and Paul Kwiat
Optical quantum information processing needs ultra-bright sources of entangled photons, especially from synchronizable femtosecond lasers and low-cost cw-diode lasers. Decoherence due to timing information and spatial mode-dependent phase has traditionally limited the brightness of such sources. We ... [Opt. Express 17, 18920 (2009)] published Tue Dec 29, 2009.

Spin entanglement, decoherence and Bohm's EPR paradox

E. G. Cavalcanti, P. D. Drummond, H. A. Bachor, and M. D. Reid
We obtain criteria for entanglement and the EPR paradox for spin-entangled particles and analyse the effects of decoherence caused by absorption and state purity errors. For a two qubit photonic state, entanglement can occur for all transmission efficiencies. In this case, the state preparation puri ... [Opt. Express 17, 18693 (2009)] published Tue Dec 29, 2009.

Efficient generation of a maximally entangled state by repeated on- and off-resonant scattering of ancilla qubits

Kazuya Yuasa, Daniel Burgarth, Vittorio Giovannetti, and Hiromichi Nakazato
A scheme for preparing two fixed noninteracting qubits in a maximally entangled state is presented. By repeating on- and off-resonant scattering of ancilla qubits, the target qubits are driven from an arbitrary initial state into a singlet state with probability 1 (perfect efficiency). Neither the p ... [New J. Phys. 11, 123027 (2009)] published Wed Dec 30, 2009.

Entanglement detection with bounded reference frames

Fabio Costa, Nicholas Harrigan, Terry Rudolph, and Caslav Brukner
Quantum experiments usually assume the existence of perfect, classical reference frames (RFs), which allow for the specification of measurement settings (e.g. orientation of the Stern-Gerlach magnet in spin measurements) with arbitrary precision. If the RFs are `bounded' (i.e. quantum systems themse ... [New J. Phys. 11, 123007 (2009)] published Wed Dec 30, 2009.

Preparation and detection of a mechanical resonator near the ground state of motion

T. Rocheleau, T. Ndukum, C. Macklin, J. B. Hertzberg, A. A. Clerk et al.
Cold, macroscopic mechanical systems are expected to behave contrary to our usual classical understanding of reality; the most striking and counterintuitive predictions involve the existence of states in which the mechanical system is located in two places simultaneously. Various schemes have been ... [Nature 463, 72 (2010)] published Thu Jan 7, 2010.

Quantum diffraction of biphotons at a blazed grating

Martin Ostermeyer, Dirk Puhlmann, and Dietmar Korn
Correlations between photons are interesting for a number of applications and concepts in metrology, in particular for resolution improvements in different methods of quantum imaging. We demonstrate the application of a blazed grating for the characterization of the degree of spatial correlation of ... [J. Opt. Soc. Am. B 26, 2347 (2009)] published Tue Dec 29, 2009.

Private quantum decoupling and secure disposal of information

Francesco Buscemi
Given a bipartite system, correlations between its subsystems can be understood as the information that each one carries about the other. In order to give a model-independent description of secure information disposal, we propose the paradigm of private quantum decoupling, corresponding to locally r ... [New J. Phys. 11, 123002 (2009)] published Wed Dec 30, 2009.

Stabilization of a long-armed fiber-optic single-photon interferometer

Seok-Beom Cho and Tae-Gon Noh
We report on single-photon interference experiments in a Michelson-type interferometer built with two 6-km-long fiber spools, as well as on the active stabilization of the interferometer. A weak coherent light signal was (de-) multiplexed with a strong reference light using wavelength-division multi ... [Opt. Express 17, 19027 (2009)] published Tue Dec 29, 2009.

Strong no-go theorem for Gaussian quantum bit commitment

Lock Magnin, Frdric Magniez, Anthony Leverrier, and Nicolas J. Cerf
Unconditionally secure bit commitment is forbidden by quantum mechanics. We extend this no-go theorem to continuous-variable protocols where both players are restricted to use Gaussian states and operations, which is a reasonable assumption in current-state optical implementations. Our Gaussian no-g ... [Phys. Rev. A 81, 010302 ] published .

Performance of hybrid entanglement photon pair source for quantum key distribution

M. Fujiwara, M. Toyoshima, M. Sasaki, K. Yoshino, Y. Nambu et al.
We report on the experimental demonstration of a source of hybrid entanglement pairs between two different degrees of freedom, a 1550 nm time-bin qubit and an 810 nm polarization qubit. The polarization qubit at 810 nm is transformed by an asymmetric MachZehnder interferometer consisted of a Glan la ... [Appl. Phys. Lett. 95, 261103 (2009)] published Tue Dec 29, 2009.

Quantum random walks without walking

K. Manouchehri and J. B. Wang
Quantum random walks have received much interest due to their nonintuitive dynamics, which may hold the key to a new generation of quantum algorithms. What remains a major challenge is a physical realization that is experimentally viable and not limited to special connectivity criteria. We present a ... [Phys. Rev. A 80, 060304 (2009)] published Wed Dec 16, 2009.

Analysis of quantum walks with time-varying coin on d-dimensional lattices

Francesca Albertini and Domenico D'Alessandro
In this paper, we present a study of discrete time quantum walks whose underlying graph is a d-dimensional lattice. The dynamical behavior of these systems is of current interest because of their applications in quantum information theory as tools to design quantum algorithms. We assume that, at eac ... [J. Math. Phys. 50, 122106 (2009)] published Tue Dec 29, 2009.

Quantum algorithms for algebraic problems

Andrew M. Childs and Wim van Dam
Quantum computers can execute algorithms that dramatically outperform classical computation. As the best-known example, Shor discovered an efficient quantum algorithm for factoring integers, whereas factoring appears to be difficult for classical computers. Understanding what other computational pro ... [Rev. Mod. Phys. 82, 1 ] published .

First-Order Phase Transition in the Quantum Adiabatic Algorithm

A. P. Young, S. Knysh, and V. N. Smelyanskiy
We simulate the quantum adiabatic algorithm (QAA) for the exact cover problem for sizes up to N=256 using quantum MonteCarlo simulations incorporating parallel tempering. At large N, we find that some instances have a discontinuous (first-order) quantum phase transition during the evolution of the Q ... [Phys. Rev. Lett. 104, 020502 ] published .

Wave Communication across Regular Lattices

Birgit Hein and Gregor Tanner
We propose a novel way to communicate signals in the form of waves across a d-dimensional lattice. The mechanism is based on quantum search algorithms and makes it possible to both search for marked positions in a regular grid and to communicate between two (or more) points on the lattice. Remarkabl ... [Phys. Rev. Lett. 103, 260501 (2009)] published Tue Dec 22, 2009.

Experimental Approximation of the Jones Polynomial with One Quantum Bit

G. Passante, O. Moussa, C. A. Ryan, and R. Laflamme
We present experimental results approximating the Jones polynomial using 4 qubits in a liquid state nuclear magnetic resonance quantum information processor. This is the first experimental implementation of a complete problem for the deterministic quantum computation with one quantum bit model of qu ... [Phys. Rev. Lett. 103, 250501 (2009)] published Fri Dec 18, 2009.

Quantum position diffusion and its implications for the quantum linear Boltzmann equation

I. Kamleitner and J. Cresser
We derive a quantum linear Boltzmann equation from first principles to describe collisional friction, diffusion, and decoherence in a unified framework. In doing so, we discover that the previously celebrated quantum contribution to position diffusion is not a true physical process, but rather an ar ... [Phys. Rev. A 81, 012107 ] published .

Computation on spin chains with limited access

Alastair Kay and Peter J. Pemberton-Ross
We show how to implement quantum computation on a system with an intrinsic Hamiltonian by controlling a limited subset of spins. Our primary result is an efficient control sequence on a nearest-neighbor XY spin chain through control of a single site and its interaction with its neighbor. Control of ... [Phys. Rev. A 81, 010301 ] published .

Transitions in the computational power of thermal states for measurement-based quantum computation

Sean D. Barrett, Stephen D. Bartlett, Andrew C. Doherty, David Jennings, and Terry Rudolph
We show that the usefulness of the thermal state of a specific spin-lattice model for measurement-based quantum computing exhibits a transition between two distinct phasesone in which every state is a universal resource for quantum computation, and another in which any local measurement sequence can ... [Phys. Rev. A 80, 062328 (2009)] published Fri Dec 18, 2009.

Photonic quantum technologies

Jeremy L. O'Brien, Akira Furusawa, and Jelena VuCkovic
The first quantum technology that harnesses quantum mechanical effects for its core operation has arrived in the form of commercially available quantum key distribution systems. This technology achieves enhanced security by encoding information in photons such that an eavesdropper in the system can ... [Nat. Photonics 3, 687 (2009)] published Mon Nov 30, 2009.