Localization-delocalization transitions in a two-dimensional quantum percolation model: von Neumann entropy studies
Longyan Gong and Peiqing Tong
In two-dimensional quantum site-percolation square lattice models, the von Neumann entropy is extensively studied numerically. At a certain eigenenergy, the localization-delocalization transition is reflected by the derivative of von Neumann entropy which is maximal at the quantum percolation thresh ... [Phys. Rev. B 80, 174205 (2009)] published Fri Nov 20, 2009.
Engineering quantum operations on traveling light beams by multiple photon addition and subtraction
Jaromir Fiurasek
We propose and investigate an optical scheme for probabilistic implementation of an arbitrary single-mode quantum operation that can be expressed as a function of photon number operator. The scheme coherently combines multiple photon addition and subtraction and is feasible with current technology. ... [Phys. Rev. A 80, 053822 (2009)] published Mon Nov 16, 2009.
Information propagation through quantum chains with fluctuating disorder
Christian K. Burrell, Jens Eisert, and Tobias J. Osborne
We investigate the propagation of information through one-dimensional nearest-neighbor interacting quantum spin chains in the presence of external fields which fluctuate independently on each site. We study two fundamentally different models: (i) a model with general nearest-neighbor interactions in ... [Phys. Rev. A 80, 052319 (2009)] published Thu Nov 12, 2009.
Breakdown of the dipole blockade with a zero-area phase-jump pulse
Jun Qian, Yong Qian, Min Ke, Xun-Li Feng, C. H. Oh et al.
We theoretically investigate the effect of a zero-area pulse on the excitations of interacting Rydberg atoms. The unexpected breakdown of dipole blockade occurs in the strong Rydberg blockade regime, which results from the nonadiabatic character of a phase-jump pulse interacting with the atoms. We a ... [Phys. Rev. A 80, 053413 (2009)] published Thu Nov 12, 2009.
Optimum unambiguous discrimination of linearly independent pure states
Shengshi Pang (庞盛世) and Shengjun Wu (吴盛俊)
Given n linearly independent pure states and their prior probabilities, we study the optimum unambiguous state discrimination problem. We derive the conditions for the optimum measurement strategy to achieve the maximum average success probability and establish two sets of equations that must be sat ... [Phys. Rev. A 80, 052320 (2009)] published Thu Nov 12, 2009.
Unambiguous comparison of quantum measurements
Mario Ziman, Teiko Heinosaari, and Michal Sedlak
The goal of comparison is to reveal the difference of compared objects as fast and reliably as possible. In this paper we formulate and investigate the unambiguous comparison of unknown quantum measurements represented by nondegenerate sharp positive operator valued measures. We distinguish between ... [Phys. Rev. A 80, 052102 (2009)] published Thu Nov 5, 2009.
Erratum: Efficient Dynamic Nuclear Polarization at High Magnetic Fields [Phys. Rev. Lett. 98, 220501 (2007)]
Gavin W. Morley, Johan van Tol, Arzhang Ardavan, Kyriakos Porfyrakis, Jinying Zhang et al.
Abstract not available. [Phys. Rev. Lett. 103, 199902 (2009)] published Thu Nov 5, 2009.
Minimum error discrimination problem for pure qubit states
Boris F. Samsonov
The necessary and sufficient conditions for minimization of the generalized rate error for discriminating among N pure qubit states are reformulated in terms of Bloch vectors representing the states. For the direct optimization problem, an algorithmic solution to these conditions is indicated. A sol ... [Phys. Rev. A 80, 052305 (2009)] published Wed Nov 4, 2009.
Contraction of fermionic operator circuits and the simulation of strongly correlated fermions
Thomas Barthel, Carlos Pineda, and Jens Eisert
A fermionic operator circuit is a product of fermionic operators of usually different and partially overlapping support. Further elements of fermionic operator circuits (FOCs) are partial traces and partial projections. The presented framework allows for the introduction of fermionic versions of kno ... [Phys. Rev. A 80, 042333 (2009)] published Fri Oct 30, 2009.
Concavity of the set of quantum probabilities for any given dimension
Karoly F. Pal and Tamas Vertesi
Let us consider the set of all probabilities generated by local binary measurements on two separated quantum systems of a given local dimension d. We address the question of whether the shape of this quantum body is convex or not. We construct a point in the space of probabilities, which is on the c ... [Phys. Rev. A 80, 042114 (2009)] published Fri Oct 30, 2009.
Fermionic multiscale entanglement renormalization ansatz
Philippe Corboz and Guifre Vidal
In a recent contribution [P. Corboz, G. Evenbly, F. Verstraete, and G. Vidal, arXiv:0904.4151 (unpublished)] entanglement renormalization was generalized to fermionic lattice systems in two spatial dimensions. Entanglement renormalization is a real-space coarse-graining transformation for lattice sy ... [Phys. Rev. B 80, 165129 (2009)] published Thu Oct 29, 2009.
Driving quantum-walk spreading with the coin operator
A. Romanelli
We generalize the discrete quantum walk on the line using a time-dependent unitary coin operator. We find an analytical relation between the long-time behaviors of the standard deviation and the coin operator. Selecting the coin time sequence allows to obtain a variety of predetermined asymptotic wa ... [Phys. Rev. A 80, 042332 (2009)] published Thu Oct 29, 2009.
Spatial reflection and associated string order in quantum spin chains
Li-Xiang Cen
We investigate spatial reflection and associated nonlocal order in spin-chain quantum systems. The proposed string order parameters, e.g., reflected via operations of the spatial reflection or combinations of it with spin reflection, are able to characterize a variety of physical systems and allow u ... [Phys. Rev. B 80, 132405 (2009)] published Tue Oct 20, 2009.
Geometric phase of interacting qubits: Mean-field analysis
J. Dajka, M. Mierzejewski, and J. Luczka
We consider a system consisting of a large number of interacting qubits and study the geometric phase of one of them. The many body interaction is analyzed within a mean-field approach when the reduced dynamics of a single qubit is described by a nonlinear Hartree equation. Generally, the geometric ... [Phys. Rev. A 80, 044303 (2009)] published Mon Oct 19, 2009.
Quantum Monte Carlo Simulations of Fidelity at Magnetic Quantum Phase Transitions
David Schwandt, Fabien Alet, and Sylvain Capponi
When a system undergoes a quantum phase transition, the ground-state wave function shows a change of nature, which can be monitored using the fidelity concept. We introduce two quantum Monte Carlo schemes that allow the computation of fidelity and its susceptibility for large interacting many-body s ... [Phys. Rev. Lett. 103, 170501 (2009)] published Mon Oct 19, 2009.
Optimal two-copy discrimination of quantum measurements
Jaromir Fiurasek and Michal MiCuda
We investigate optimal discrimination between two projective quantum measurements on a single qubit. We consider a scenario where the measurement that should be identified can be performed twice and we show that adaptive discrimination strategy, entangled probe states, and feed forward all help to i ... [Phys. Rev. A 80, 042312 (2009)] published Fri Oct 16, 2009.
Canonical phase measurement is pure
Teiko Heinosaari and Juha-Pekka Pellonpaa
We show that the canonical phase measurement is pure in the sense that the corresponding positive operator valued measure (POVM) is extremal in the convex set of all POVMs. This means that the canonical phase measurement cannot be interpreted as a noisy measurement even if it is not a projection val ... [Phys. Rev. A 80, 040101 (2009)] published Thu Oct 8, 2009.
Entropic uncertainties for joint quantum measurements
Thomas Brougham, Erika Andersson, and Stephen M. Barnett
We investigate the uncertainty associated with a joint quantum measurement of two spin components of a spin-(1/2) particle and quantify this in terms of entropy. We consider two entropic quantities, the joint entropy and the sum of the marginal entropies, and obtain lower bounds for each of these qu ... [Phys. Rev. A 80, 042106 (2009)] published Wed Oct 7, 2009.
Critical exponents with a multiscale entanglement renormalization Ansatz channel
S. Montangero, M. Rizzi, V. Giovannetti, and Rosario Fazio
We show how to compute the critical exponents of one-dimensional quantum critical systems in the thermodynamic limit. The method is based on an iterative scheme applied to the multiscale entanglement renormalization Ansatz for the ground-state wave function. We test this scheme to compute the critic ... [Phys. Rev. B 80, 113103 (2009)] published Wed Sep 30, 2009.
Local and global statistical distances are equivalent on pure states
Scott M. Cohen
The statistical distance between pure quantum states is obtained by finding a measurement that is optimal in a sense defined by Wootters. As such, one may expect that the statistical distance will turn out to be different if the set of possible measurements is restricted in some way. It nonetheless ... [Phys. Rev. A 80, 032323 (2009)] published Tue Sep 22, 2009.
Wigner-function theory and decoherence of the quantum-injected optical parametric amplifier
Nicolo Spagnolo, Chiara Vitelli, Tiziano De Angelis, Fabio Sciarrino, and Francesco De Martini
Recent experimental results demonstrated the generation of a macroscopic quantum superposition (MQS), involving a number of photons in excess of 5 x 10, which showed a high resilience to losses. In order to perform a complete analysis on the effects of decoherence on these multiphoton fields, obtain ... [Phys. Rev. A 80, 032318 (2009)] published Thu Sep 17, 2009.