580 research outputs found
The Majorization Arrow in Quantum Algorithm Design
We apply majorization theory to study the quantum algorithms known so far and
find that there is a majorization principle underlying the way they operate.
Grover's algorithm is a neat instance of this principle where majorization
works step by step until the optimal target state is found. Extensions of this
situation are also found in algorithms based in quantum adiabatic evolution and
the family of quantum phase-estimation algorithms, including Shor's algorithm.
We state that in quantum algorithms the time arrow is a majorization arrow.Comment: REVTEX4.b4 file, 4 color figures (typos corrected.
Negotiating safety practice in small construction companies
AbstractSmall construction companies have high rates of work related injuries and pervasive challenges in preventing them. This article examines safety practice from the employee perspective, taking into account the role of the owner–manager and interactions with customers in everyday work settings. Data were derived from a qualitative multi-case study of ten small construction companies (carpentry/plumbing/masonry) involving one or two-man work crews. The analytic approach is phenomenological, based on thematic content analysis of interviews and participant-observations. The employees’ general approach to safety was “to take care of oneself”, which, in addition to standardized rule-based knowledge, drew on individual feelings, personal experience and the balancing of various concerns in different work settings, e.g. workflow, customer satisfaction, good work relations and safety issues. In the context of small companies, safety practice was negotiated in the tension between owner–manager decisions and employees’ self-administration, which also was reflected in the way safety was communicated and learned within the companies as a matter of professionalism and individual mastering. Safety was rarely in explicit focus among employees in the small construction companies. It was an intrinsic part of their craftsmanship, established and negotiated in work situations and in interactions, in particular with customers. Safety issues were rarely shared or communicated as a common issue within the company. Consequently owner–managers had limited impact on the employees’ daily safety practices. Injury prevention approaches should take into account the limited impact that owner–managers had on the day-to-day safety practices, as well as the importance of the employees’ relationships with the customers
SU(2) Yang-Mills Theory with extended Supersymmetry in a Background Magnetic Field
The vacuum structure of N=2 (and N=4) SUSY Yang-Mills theory is analyzed in
detail by considering the effective potential for constant background scalar-
magnetic fields within different approximations. We compare the one-loop
approximation with- or without instanton improved effective coupling with the
one-loop result in the dual desription. For N=2 we find that non-perturbative
monopole degrees of freedom remove the non-trivial minima present in the
(improved) one-loop potential in the strong-coupling regime. The combination of
Yang-Mills and dual desription leads to a self-consistent effective potential
over the full range of background fields.Comment: 15 pages, Revtex, 3 figures, References added, section two shortened,
some minor remarks and corrections adde
Implementation of a Deutsch-like quantum algorithm utilizing entanglement at the two-qubit level, on an NMR quantum information processor
We describe the experimental implementation of a recently proposed quantum
algorithm involving quantum entanglement at the level of two qubits using NMR.
The algorithm solves a generalisation of the Deutsch problem and distinguishes
between even and odd functions using fewer function calls than is possible
classically. The manipulation of entangled states of the two qubits is
essential here, unlike the Deutsch-Jozsa algorithm and the Grover's search
algorithm for two bits.Comment: 4 pages, two eps figure
Experimental requirements for Grover's algorithm in optical quantum computation
The field of linear optical quantum computation (LOQC) will soon need a
repertoire of experimental milestones. We make progress in this direction by
describing several experiments based on Grover's algorithm. These experiments
range from a relatively simple implementation using only a single non-scalable
CNOT gate to the most complex, requiring two concatenated scalable CNOT gates,
and thus form a useful set of early milestones for LOQC. We also give a
complete description of basic LOQC using polarization-encoded qubits, making
use of many simplifications to the original scheme of Knill, Laflamme, and
Milburn.Comment: 9 pages, 8 figure
Realization of quantum process tomography in NMR
Quantum process tomography is a procedure by which the unknown dynamical
evolution of an open quantum system can be fully experimentally characterized.
We demonstrate explicitly how this procedure can be implemented with a nuclear
magnetic resonance quantum computer. This allows us to measure the fidelity of
a controlled-not logic gate and to experimentally investigate the error model
for our computer. Based on the latter analysis, we test an important assumption
underlying nearly all models of quantum error correction, the independence of
errors on different qubits.Comment: 8 pages, 7 EPS figures, REVTe
Experimental Implementation of the Quantum Random-Walk Algorithm
The quantum random walk is a possible approach to construct new quantum
algorithms. Several groups have investigated the quantum random walk and
experimental schemes were proposed. In this paper we present the experimental
implementation of the quantum random walk algorithm on a nuclear magnetic
resonance quantum computer. We observe that the quantum walk is in sharp
contrast to its classical counterpart. In particular, the properties of the
quantum walk strongly depends on the quantum entanglement.Comment: 5 pages, 4 figures, published versio
Effect of Dynamical SU(2) Gluons to the Gap Equation of Nambu--Jona-Lasinio Model in Constant Background Magnetic Field
In order to estimate the effect of dynamical gluons to chiral condensate, the
gap equation of SU(2) gauged Nambu--Jona-Lasinio model, under a constant
background magnetic field, is investigated up to the two-loop order in 2+1 and
3+1 dimensions. We set up a general formulation allowing both cases of electric
as well as magnetic background field. We rely on the proper time method to
maintain gauge invariance. In 3+1 dimensions chiral symmetry breaking
(SB) is enhanced by gluons even in zero background magnetic field and
becomes much striking as the background field grows larger. In 2+1 dimensions
gluons also enhance SB but whose dependence on the background field is
not simple: dynamical mass is not a monotone function of background field for a
fixed four-fermi coupling.Comment: 20 pages, 5 figure
Excess mortality among the elderly in european countries, December 2014 to February 2015
Since December 2014 and up to February 2015, the weekly number of excess deaths from all-causes among individuals ≥ 65 years of age in 14 European countries have been significantly higher than in the four previous winter seasons. The rise in unspecified excess mortality coincides with increased proportion of influenza detection in the European influenza surveillance schemes with a main predominance of influenza A(H3N2) viruses seen throughout Europe in the current season, though cold snaps and other respiratory infections may also have had an effect
Measurement of qubits
We describe in detail the theory underpinning the measurement of density matrices of a pair of quantum two-level systems (qubits). Our particular emphasis is on qubits realized by the two polarization degrees of freedom of a pair of entangled photons generated in a down-conversion experiment; however, the discussion applies in general, regardless of the actual physical realization. Two techniques are discussed, namely, a tomographic reconstruction (in which the density matrix is linearly related to a set of measured quantities) and a maximum likelihood technique which requires numerical optimization (but has the advantage of producing density matrices that are always non-negative definite). In addition, a detailed error analysis is presented, allowing errors in quantities derived from the density matrix, such as the entropy or entanglement of formation, to be estimated. Examples based on down-conversion experiments are used to illustrate our results
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