143 research outputs found
Quantum Control of Two-Qubit Entanglement Dissipation
We investigate quantum control of the dissipation of entanglement under
environmental decoherence. We show by means of a simple two-qubit model that
standard control methods - coherent or open-loop control - will not in general
prevent entanglement loss. However, we propose a control method utilising a
Wiseman-Milburn feedback/measurement control scheme which will effectively
negate environmental entanglement dissipation.Comment: 11 pages,4 figures, minor correctio
Symmetries of Snyder--de Sitter space and relativistic particle dynamics
We study the deformed conformal-Poincare symmetries consistent with the
Snyder--de Sitter space. A relativistic particle model invariant under these
deformed symmetries is given. This model is used to provide a gauge independent
derivation of the Snyder--de Sitter algebra. Our results are valid in the
leading order in the parameters appearing in the model.Comment: 12 pages, LaTeX, version appearing in JHEP, minor changes to match
published versio
Qubit portrait of the photon-number tomogram and separability of two-mode light states
In view of the photon-number tomograms of two-mode light states, using the
qubit-portrait method for studying the probability distributions with infinite
outputs, the separability and entanglement detection of the states are studied.
Examples of entangled Gaussian state and Schr\"{o}dinger cat state are
discussed.Comment: 20 pages, 6 figures, TeX file, to appear in Journal of Russian Laser
Researc
Operational approach to open dynamics and quantifying initial correlations
A central aim of physics is to describe the dynamics of physical systems.
Schrodinger's equation does this for isolated quantum systems. Describing the
time evolution of a quantum system that interacts with its environment, in its
most general form, has proved to be difficult because the dynamics is dependent
on the state of the environment and the correlations with it. For discrete
processes, such as quantum gates or chemical reactions, quantum process
tomography provides the complete description of the dynamics, provided that the
initial states of the system and the environment are independent of each other.
However, many physical systems are correlated with the environment at the
beginning of the experiment. Here, we give a prescription of quantum process
tomography that yields the complete description of the dynamics of the system
even when the initial correlations are present. Surprisingly, our method also
gives quantitative expressions for the initial correlation.Comment: Completely re-written for clarity of presentation. 15 pages and 2
figure
Gauge symmetry and W-algebra in higher derivative systems
The problem of gauge symmetry in higher derivative Lagrangian systems is
discussed from a Hamiltonian point of view. The number of independent gauge
parameters is shown to be in general {\it{less}} than the number of independent
primary first class constraints, thereby distinguishing it from conventional
first order systems. Different models have been considered as illustrative
examples. In particular we show a direct connection between the gauge symmetry
and the W-algebra for the rigid relativistic particle.Comment: 1+22 pages, 1 figure, LaTeX, v2; title changed, considerably expanded
version with new results, to appear in JHE
MuSR method and tomographic probability representation of spin states
Muon spin rotation/relaxation/resonance (MuSR) technique for studying matter
structures is considered by means of a recently introduced probability
representation of quantum spin states. A relation between experimental MuSR
histograms and muon spin tomograms is established. Time evolution of muonium,
anomalous muonium, and a muonium-like system is studied in the tomographic
representation. Entanglement phenomenon of a bipartite muon-electron system is
investigated via tomographic analogues of Bell number and positive partial
transpose (PPT) criterion. Reconstruction of the muon-electron spin state as
well as the total spin tomography of composed system is discussed.Comment: 20 pages, 4 figures, LaTeX, submitted to Journal of Russian Laser
Researc
Symmetric informationally complete positive operator valued measure and probability representation of quantum mechanics
Symmetric informationally complete positive operator valued measures
(SIC-POVMs) are studied within the framework of the probability representation
of quantum mechanics. A SIC-POVM is shown to be a special case of the
probability representation. The problem of SIC-POVM existence is formulated in
terms of symbols of operators associated with a star-product quantization
scheme. We show that SIC-POVMs (if they do exist) must obey general rules of
the star product, and, starting from this fact, we derive new relations on
SIC-projectors. The case of qubits is considered in detail, in particular, the
relation between the SIC probability representation and other probability
representations is established, the connection with mutually unbiased bases is
discussed, and comments to the Lie algebraic structure of SIC-POVMs are
presented.Comment: 22 pages, 1 figure, LaTeX, partially presented at the Workshop
"Nonlinearity and Coherence in Classical and Quantum Systems" held at the
University "Federico II" in Naples, Italy on December 4, 2009 in honor of
Prof. Margarita A. Man'ko in connection with her 70th birthday, minor
misprints are corrected in the second versio
Optimal error estimation for H(curl)-conforming p-interpolation in two dimensions
In this paper we prove an optimal error estimate for the H(curl)-conforming
projection based p-interpolation operator introduced in [L. Demkowicz and I.
Babuska, p interpolation error estimates for edge finite elements of variable
order in two dimensions, SIAM J. Numer. Anal., 41 (2003), pp. 1195-1208]. This
result is proved on the reference element (either triangle or square) K for
regular vector fields in H^r(curl,K) with arbitrary r>0. The formulation of the
result in the H(div)-conforming setting, which is relevant for the analysis of
high-order boundary element approximations for Maxwell's equations, is provided
as well
A squeezed review on coherent states and nonclassicality for non-Hermitian systems with minimal length
It was at the dawn of the historical developments of quantum mechanics when Schrödinger, Kennard and Darwin proposed an interesting type of Gaussian wave packets, which do not spread out while evolving in time. Originally, these wave packets are the prototypes of the renowned discovery, which are familiar as “coherent states” today. Coherent states are inevitable in the study of almost all areas of modern science, and the rate of progress of the subject is astonishing nowadays. Nonclassical states constitute one of the distinguished branches of coherent states having applications in various subjects including quantum information processing, quantum optics, quantum superselection principles and mathematical physics. On the other hand, the compelling advancements of non-Hermitian systems and related areas have been appealing, which became popular with the seminal paper by Bender and Boettcher in 1998. The subject of non-Hermitian Hamiltonian systems possessing real eigenvalues are exploding day by day and combining with almost all other subjects rapidly, in particular, in the areas of quantum optics, lasers and condensed matter systems, where one finds ample successful experiments for the proposed theory. For this reason, the study of coherent states for non-Hermitian systems have been very important. In this article, we review the recent developments of coherent and nonclassical states for such systems and discuss their applications and usefulness in different contexts of physics. In addition, since the systems considered here originated from the broader context of the study of minimal uncertainty relations, our review is also of interest to the mathematical physics communit
Magnetic and Electronic Properties of Metal-Atom Adsorbed Graphene
We systematically investigate the magnetic and electronic properties of
graphene adsorbed with diluted 3d-transition and noble metal atoms using first
principles calculation methods. We find that most transition metal atoms (i.e.
Sc, Ti, V, Mn, Fe) favor the hollow adsorption site, and the interaction
between magnetic adatoms and \pi-orbital of graphene induces sizable exchange
field and Rashba spin-orbit coupling, which together open a nontrivial bulk gap
near the Dirac points leading to the quantum-anomalous Hall effect. We also
find that the noble metal atoms (i.e. Cu, Ag, Au) prefer the top adsorption
site, and the dominant inequality of the AB sublattice potential opens another
kind of nontrivial bulk gap exhibiting the quantum-valley Hall effect.Comment: Submitted to PRL on Aug. 10, 2011. 11 pages(4.5 pages for the main
text and 6.5 pages for the supporting materials
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