Physical Review A
Robust entanglement in antiferromagnetic Heisenberg chains by single-spin optimal control
Author(s): Xiaoting Wang, Abolfazl Bayat, S. G. Schirmer, and Sougato Bose
We demonstrate how near-perfect entanglement (in fact arbitrarily close to maximal entanglement) can be generated between the end spins of an antiferromagnetic isotropic Heisenberg chain of length N, starting from the ground state in the N/2 excitation subspace, by applying a magnetic field along a ...
[Phys. Rev. A 81, 032312] Published Thu Mar 11, 2010
Universality of the negativity in the Lipkin-Meshkov-Glick model
Author(s): Hannu Wichterich, Julien Vidal, and Sougato Bose
The entanglement between noncomplementary blocks of a many-body system, where a part of the system forms an ignored environment, is a largely untouched problem without analytic results. We rectify this gap by studying the logarithmic negativity between two macroscopic sets of spins in an arbitrary t...
[Phys. Rev. A 81, 032311] Published Thu Mar 11, 2010
Protection of quantum information and optimal singlet conversion through higher-dimensional quantum systems and environment monitoring
Author(s): E. Mascarenhas, B. Marques, D. Cavalcanti, M. Terra Cunha, and M. França Santos
We study how to protect quantum information in quantum systems subjected to local dissipation. We show that combining the use of three-level systems, environment monitoring, and local feedback can fully and deterministically protect any available quantum information, including entanglement initially...
[Phys. Rev. A 81, 032310] Published Thu Mar 11, 2010
Grover-like search via a Frenkel-exciton trapping mechanism
Author(s): A. Thilagam
We propose the physical implementation of a Grover-like search problem by means of Frenkel exciton trapping at a shallow isotopic impurity against a background of competing mechanisms. The search, culminating at the impurity molecule, designated the “winner” site, is marked by its enhanced inter...
[Phys. Rev. A 81, 032309] Published Wed Mar 10, 2010
Necessary condition for the quantum adiabatic approximation
Author(s): S. Boixo and R. D. Somma
A gapped quantum system that is adiabatically perturbed remains approximately in its eigenstate after the evolution. We prove that, for constant gap, general quantum processes that approximately prepare the final eigenstate require a minimum time proportional to the ratio of the length of the eigens...
[Phys. Rev. A 81, 032308] Published Tue Mar 09, 2010
Deterministic entanglement purification and complete nonlocal Bell-state analysis with hyperentanglement
Author(s): Yu-Bo Sheng and Fu-Guo Deng
Entanglement purification is a very important element for long-distance quantum communication. Different from all the existing entanglement purification protocols (EPPs) in which two parties can only obtain some quantum systems in a mixed entangled state with a higher fidelity probabilistically by c...
[Phys. Rev. A 81, 032307] Published Tue Mar 09, 2010
One-way quantum computation with circuit quantum electrodynamics
Author(s): Chun-Wang Wu, Yang Han, Xiao-Jun Zhong, Ping-Xing Chen, and Cheng-Zu Li
In this Brief Report, we propose a potential scheme to implement one-way quantum computation with circuit quantum electrodynamics (QED). Large cluster states of charge qubits can be generated in just one step with a superconducting transmission line resonator (TLR) playing the role of a dispersive c...
[Phys. Rev. A 81, 034301] Published Mon Mar 08, 2010
Geometric measures of entanglement
Author(s): K. Uyanık and S. Turgut
The geometric measure of entanglement, which expresses the minimum distance to product states, has been generalized to distances to sets that remain invariant under the stochastic reducibility relation. For each such set, an associated entanglement monotone can be defined. The explicit analytical fo...
[Phys. Rev. A 81, 032306] Published Mon Mar 08, 2010
Decoherence in a dynamical quantum phase transition
Author(s): Sarah Mostame, Gernot Schaller, and Ralf Schützhold
Motivated by the similarity between adiabatic quantum algorithms and quantum phase transitions, we study the impact of decoherence on the sweep through a second-order quantum phase transition for the prototypical example of the Ising chain in a transverse field and compare it to the adiabatic versio...
[Phys. Rev. A 81, 032305] Published Mon Mar 08, 2010
Multipartite entanglement measures and quantum criticality from matrix and tensor product states
Author(s): Ching-Yu Huang and Feng-Li Lin
We compute the multipartite entanglement measures such as the global entanglement of various one- and two-dimensional quantum systems to probe the quantum criticality based on the matrix and tensor product states (MPSs and TPSs). We use the infinite time-evolving block decimation (iTEBD) method to f...
[Phys. Rev. A 81, 032304] Published Fri Mar 05, 2010
Quantum-information-processing architecture with endohedral fullerenes in a carbon nanotube
Author(s): W. L. Yang, Z. Y. Xu, H. Wei, M. Feng, and D. Suter
A potential quantum-information processor is proposed using an array of the endohedral fullerenes 15N@C60 or 31P@C60 contained in a single walled carbon nanotube (SWCNT). The qubits are encoded in the nuclear spins of the doped atoms, while the electronic spins are used for initialization and readou...
[Phys. Rev. A 81, 032303] Published Fri Mar 05, 2010
Phase gate and readout with an atom-molecule hybrid platform
Author(s): Elena Kuznetsova, Marko Gacesa, Susanne F. Yelin, and Robin Côté
In order to optimize quantum information processing in individual traps such as optical lattices, we propose a combined atom-molecule system. In particular, gates, initialization, and readout are suggested, using two atoms of different species—one atom carrying the qubit and the other enabling int...
[Phys. Rev. A 81, 030301] Published Thu Mar 04, 2010
Greenberger-Horne-Zeilinger and W entanglement witnesses for the noninteracting Fermi gas
Author(s): Hessam Habibian, John W. Clark, Naeimeh Behbood, and Kurt Hingerl
The existence and nature of tripartite entanglement of a noninteracting Fermi gas (NIFG) is investigated. Three classes of parametrized entanglement witnesses (EWs) are introduced with the aim of detecting genuine tripartite entanglement in the three-body reduced density matrix and discriminating be...
[Phys. Rev. A 81, 032302] Published Wed Mar 03, 2010
Topological subsystem codes
Author(s): H. Bombin
We introduce a family of two-dimensional (2D) topological subsystem quantum error-correcting codes. The gauge group is generated by two-local Pauli operators, so that two-local measurements are enough to recover the error syndrome. We study the computational power of code deformation in these codes ...
[Phys. Rev. A 81, 032301] Published Wed Mar 03, 2010
Entanglement monogamy inequality in a 2⊗2⊗4 system
Author(s): Xi-Jun Ren and Wei Jiang
In this report, we show explicitly that the tangles of an arbitrary pure state in a 2⊗2⊗4 system satisfy the monogamy relation. This relation is also generalized to mixed states. As the tangle is always larger than the square of the concurrence, our result implies that the monogamy relation hold...
[Phys. Rev. A 81, 024305] Published Fri Feb 26, 2010
Qubit transfer between photons at telecom and visible wavelengths in a slow-light atomic medium
Author(s): A. Gogyan
We propose a method that enables efficient conversion of the quantum information frequency between different regions of a spectrum of light based on recently demonstrated strong parametric coupling between two narrow-band single-photon pulses propagating in a slow-light atomic medium [N. Sisakyan an...
[Phys. Rev. A 81, 024304] Published Thu Feb 25, 2010
Quantum logic as superbraids of entangled qubit world lines
Author(s): Jeffrey Yepez
Presented is a topological representation of quantum logic that views entangled qubit spacetime histories (or qubit world lines) as a generalized braid, referred to as a superbraid. The crossing of world lines can be quantum-mechanical in nature, most conveniently expressed analytically with ladder-...
[Phys. Rev. A 81, 022328] Published Thu Feb 25, 2010
Entanglement and perfect discrimination of a class of multiqubit states by local operations and classical communication
Author(s): Somshubhro Bandyopadhyay
It is shown that while entanglement ensures difficulty in discriminating a set of mutually orthogonal states perfectly by local operations and classical communication (LOCC), entanglement content does not. In particular, for a class of entangled multiqubit states, the maximum number of perfectly LOC...
[Phys. Rev. A 81, 022327] Published Thu Feb 25, 2010
Multipartite W states for chains of atoms conveyed through an optical cavity
Author(s): D. Gonţa and S. Fritzsche
We propose and work out a scheme to generate the entangled W states for a chain of N four-level atoms which are transported through an optical cavity by means of an optical lattice. This scheme is based on the combined laser-cavity mediated interaction between distant and equally separated atoms and...
[Phys. Rev. A 81, 022326] Published Thu Feb 25, 2010
Tight bound on coherent-state-based entanglement generation over lossy channels
Author(s): Koji Azuma, Naoya Sota, Masato Koashi, and Nobuyuki Imoto
The first stage of the hybrid quantum repeaters is entanglement generation based on transmission of pulses in coherent states over a lossy channel. Protocols to make entanglement with only one type of error are favorable for rendering subsequent entanglement distillation efficient. Here we provide t...
[Phys. Rev. A 81, 022325] Published Thu Feb 25, 2010
