Physical Review A

Author(s): Xiao-Qiang Xi and Ming-Liang Hu

Although Han et al. [Phys. Rev. Lett. 98, 150404 (2007)] proposed a quantum circuit with six qubits to demonstrate the basic braiding statistics of anyons, we have found that a four-qubit system is enough for realizing such a process. We call it the minimum unit for the fractional statistics of anyo...

[Phys. Rev. A 82, 024303] Published Mon Aug 30, 2010

Author(s): Jaromír Fiurášek

We propose and investigate a protocol for Gaussification of quantum states of traveling light beams in an atomic quantum memory that couples to light via quantum nondemolition (QND) interaction. The protocol relies on a periodic switching between two different QND couplings and the total coupling st...

[Phys. Rev. A 82, 022334] Published Mon Aug 30, 2010

Author(s): Hari Krovi, Maris Ozols, and Jérémie Roland

We present an adiabatic quantum algorithm for the abstract problem of searching marked vertices in a graph, or spatial search. Given a random walk (or Markov chain) P on a graph with a set of unknown marked vertices, one can define a related absorbing walk P' where outgoing transitions from marked v...

[Phys. Rev. A 82, 022333] Published Mon Aug 30, 2010

Author(s): E. B. Fel’dman, E. I. Kuznetsova, and A. I. Zenchuk

This article is devoted to the development of analytical and numerical approaches to the problem of the end-to-end quantum state transfer along the spin-1/2 chain using two methods: (a) a homogeneous spin chain with week end bonds and equal Larmor frequencies and (b) a homogeneous spin chain with en...

[Phys. Rev. A 82, 022332] Published Mon Aug 30, 2010

Author(s): Qing Lin and Bing He

We present a scheme to generate any two-dimensional cluster state efficiently. The number of the basic gate (entangler) operations is on the order of the entanglement bonds of a cluster state. This deterministic scheme, which demands few ancilla resources and no quantum memory, is suitable for large...

[Phys. Rev. A 82, 022331] Published Mon Aug 30, 2010

Author(s): Stephanie Simmons, Jonathan A. Jones, Steven D. Karlen, Arzhang Ardavan, and John J. L. Morton

Measurement devices could benefit from entangled correlations to yield a measurement sensitivity approaching the physical Heisenberg limit. Building upon previous magnetometric work using pseudoentangled spin states in solution-state NMR, we present two conceptual advancements to better prepare and ...

[Phys. Rev. A 82, 022330] Published Thu Aug 26, 2010

Author(s): M. Al-Amri, Jörg Evers, and M. Suhail Zubairy

A protocol for the teleportation of arbitrary quantum states of four-dimensional qudits is presented. The qudit to be teleported is encoded in the combined state of two ensembles of atoms placed in a cavity at the sender’s side. The receiver uses a similar setup, with his atoms prepared in a particu...

[Phys. Rev. A 82, 022329] Published Wed Aug 25, 2010

Author(s): O. Jiménez, Luis Roa, and A. Delgado

We study the probabilistic cloning of equidistant states. These states are such that the inner product between them is a complex constant or its conjugate. Thereby, it is possible to study their cloning in a simple way. In particular, we are interested in the behavior of the cloning probability as a...

[Phys. Rev. A 82, 022328] Published Wed Aug 25, 2010

Author(s): J. Nunn, U. Dorner, P. Michelberger, K. F. Reim, K. C. Lee, N. K. Langford, I. A. Walmsley, and D. Jaksch

Arrays of atoms trapped in optical lattices are appealing as storage media for photons, since motional dephasing of the atoms is eliminated. The regular lattice is also associated with band structure in the dispersion experienced by incident photons. Here we study the influence of this band structur...

[Phys. Rev. A 82, 022327] Published Mon Aug 23, 2010

Author(s): Deepthi Gopal and Stephanie Wehner

We consider a special form of state discrimination in which after the measurement we are given additional information that may help us identify the state. This task plays a central role in the analysis of quantum cryptographic protocols in the noisy-storage model, where the identity of the state cor...

[Phys. Rev. A 82, 022326] Published Mon Aug 23, 2010

Author(s): Yong-Cheng Ou and Mark S. Byrd

A dynamical map is a map that takes one density operator to another. Such a map can be written in an operator-sum representation (OSR) by using a spectral decomposition. The method of construction applies to general maps, which need not be completely positive. The OSR is not unique; there is freedom...

[Phys. Rev. A 82, 022325] Published Mon Aug 23, 2010

Author(s): Xiao-Ye Xu, Jin-Shi Xu, Chuan-Feng Li, and Guang-Can Guo

By using photon pairs created in parametric down-conversion, we report on an experiment, which demonstrates that measurement can recover the quantum entanglement of a two-qubit system in a pure dephasing environment. The concurrence of the final state with and without measurement is compared and is ...

[Phys. Rev. A 82, 022324] Published Mon Aug 23, 2010

Author(s): A. J. F. Hayes, H. L. Haselgrove, Alexei Gilchrist, and T. C. Ralph

We use a combination of analytical and numerical techniques to calculate the noise threshold and resource requirements for a linear optical quantum computing scheme based on parity-state encoding. Parity-state encoding is used at the lowest level of code concatenation in order to efficiently correct...

[Phys. Rev. A 82, 022323] Published Mon Aug 23, 2010

Author(s): Daniel Burgarth and Vittorio Giovannetti

In this addendum to our paper [D. Burgarth and V. Giovannetti, Phys. Rev. Lett. 99, 100501 (2007)] we prove that during the transformation that allows one to enforce control by relaxation on a quantum system, the ancillary memory can be kept at a finite size, independently from the fidelity one want...

[Phys. Rev. A 82, 024302] Published Thu Aug 19, 2010

Author(s): Sönke Niekamp, Matthias Kleinmann, and Otfried Gühne

How can one discriminate different inequivalent classes of multiparticle entanglement experimentally? We present an approach for the discrimination of an experimentally prepared state from the equivalence class of another state. We consider two possible measures for the discrimination strength of an...

[Phys. Rev. A 82, 022322] Published Thu Aug 19, 2010

Author(s): Muhammed Yönaç and J. H. Eberly

We exploit a novel approximation scheme to obtain a new and compact formula for the parameters underlying coherent-state control of the evolution of a pair of entangled two-level systems. It is appropriate for long times and for relatively strong external quantum control via coherent-state irradiati...

[Phys. Rev. A 82, 022321] Published Thu Aug 19, 2010

Author(s): Aires Ferreira, J. Viana Lopes, and J. M. B. Lopes dos Santos

We study the capacity of antiferromagnetic lattices of varying geometries to entangle two additional spin-1/2 probes. Analytical modeling of the quantum Monte Carlo data shows the appearance of a robust gap, allowing a description of entanglement in terms of probe-only states, even in cases where th...

[Phys. Rev. A 82, 022320] Published Wed Aug 18, 2010

Author(s): Jian Cui, Jun-Peng Cao, and Heng Fan

The Kitaev honeycomb model with a topological phase transition at zero temperature is studied using the quantum-information method. Based on the exact solution of the ground state, the mutual information between two nearest sites and between two bonds with the greatest distance are obtained. It is f...

[Phys. Rev. A 82, 022319] Published Mon Aug 16, 2010

Author(s): Michael Murphy, Simone Montangero, Vittorio Giovannetti, and Tommaso Calarco

Spin chains have long been considered as candidates for quantum channels to facilitate quantum communication. We consider the transfer of a single excitation along a spin-1/2 chain governed by Heisenberg-type interactions. We build on the work of Balachandran and Gong [V. Balachandran and J. Gong, P...

[Phys. Rev. A 82, 022318] Published Fri Aug 13, 2010

Author(s): Yong Shen, Hongxin Zou, Liang Tian, Pingxing Chen, and Jianmin Yuan

We present a discretely modulated continuous-variable quantum key distribution system in free space by using strong coherent states. The amplitude noise in the laser source is suppressed to the shot-noise limit by using a mode cleaner combined with a frequency shift technique. Also, it is proven tha...

[Phys. Rev. A 82, 022317] Published Fri Aug 13, 2010