1,295 research outputs found
Entanglement Energetics in the Ground State
We show how many-body ground state entanglement information may be extracted
from sub-system energy measurements at zero temperature. A precise relation
between entanglement and energy fluctuations is demonstrated in the weak
coupling limit. Examples are given with the two-state system and the harmonic
oscillator, and energy probability distributions are calculated. Comparisons
made with recent qubit experiments show this type of measurement provides
another method to quantify entanglement with the environment.Comment: 7 pages, 3 figures, Conference proceeding for the Physics of Quantum
Electronics; Utah, USA, January 200
Walks of molecular motors in two and three dimensions
Molecular motors interacting with cytoskeletal filaments undergo peculiar
random walks consisting of alternating sequences of directed movements along
the filaments and diffusive motion in the surrounding solution. An ensemble of
motors is studied which interacts with a single filament in two and three
dimensions. The time evolution of the probability distribution for the bound
and unbound motors is determined analytically. The diffusion of the motors is
strongly enhanced parallel to the filament. The analytical expressions are in
excellent agreement with the results of Monte Carlo simulations.Comment: 7 pages, 2 figures, to be published in Europhys. Let
Exact Markovian kinetic equation for a quantum Brownian oscillator
We derive an exact Markovian kinetic equation for an oscillator linearly
coupled to a heat bath, describing quantum Brownian motion. Our work is based
on the subdynamics formulation developed by Prigogine and collaborators. The
space of distribution functions is decomposed into independent subspaces that
remain invariant under Liouville dynamics. For integrable systems in
Poincar\'e's sense the invariant subspaces follow the dynamics of uncoupled,
renormalized particles. In contrast for non-integrable systems, the invariant
subspaces follow a dynamics with broken-time symmetry, involving generalized
functions. This result indicates that irreversibility and stochasticity are
exact properties of dynamics in generalized function spaces. We comment on the
relation between our Markovian kinetic equation and the Hu-Paz-Zhang equation.Comment: A few typos in the published version are correcte
Short-term variability and mass loss in Be stars III. BRITE and SMEI satellite photometry of 28 Cygni
The BRITE Constellation of nanosatellites obtained mmag photometry of 28
Cygni for 11 months in 2014-2016. Observations with the Solar Mass Ejection
Imager in 2003-2010 and 118 H line profiles were added.
For decades, 28 Cyg has exhibited four large-amplitude frequencies: two
closely spaced frequencies of spectroscopically confirmed modes near 1.5
c/d, one slightly lower exophotospheric (Stefl) frequency, and at 0.05 c/d the
difference frequency between the two g modes. This top-level framework is
indistinguishable from eta Cen (Paper I), which is also very similar in
spectral type, rotation rate, and viewing angle. The Stefl frequency is the
only one that does not seem to be affected by the difference frequency. The
amplitude of the latter undergoes large variations; around maximum the amount
of near-circumstellar matter is increased, and the amplitude of the Stefl
frequency grows by some factor. During such brightenings dozens of transient
spikes appear in the frequency spectrum, concentrated in three groups. Only
eleven frequencies were common to all years of BRITE observations.
Be stars seem to be controlled by several coupled clocks, most of which are
not very regular on timescales of weeks to months but function for decades. The
combination of g modes to the low difference frequency and/or the atmospheric
response to it appears significantly nonlinear. Like in eta Cen, the
difference-frequency variability seems the main responsible for the modulation
of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of difference
frequencies may reach the longest timescales known of the Be phenomenon.Comment: 17 pages, 21 figures, submitted to Astronomy & Astrophysic
Evidence for entangled states of two coupled flux qubits
We have studied the low-frequency magnetic susceptibility of two inductively
coupled flux qubits using the impedance measurement technique (IMT), through
their influence on the resonant properties of a weakly coupled high-quality
tank circuit. In a single qubit, an IMT dip in the tank's current--voltage
phase angle at the level anticrossing yields the amplitude of coherent flux
tunneling. For two qubits, the difference (IMT deficit) between the sum of
single-qubit dips and the dip amplitude when both qubits are at degeneracy
shows that the system is in a mixture of entangled states (a necessary
condition for entanglement). The dependence on temperature and relative bias
between the qubits allows one to determine all the parameters of the effective
Hamiltonian and equilibrium density matrix, and confirms the formation of
entangled eigenstates.Comment: 4 pages, 4 figures, final versio
Changes in trabecular bone, hematopoiesis and bone marrow vessels in aplastic anemia, primary osteoporosis, and old age
Retrospective histologic analyses of bone biopsies and of post mortem samples from normal persons of different age groups, and of bone biopsies of age- and sex-matched groups of patients with primary osteoporosis and aplastic anemia show characteristic age dependent as well as pathologic changes including atrophy of osseous trabeculae and of hematopoiesis, and changes in the sinusoidal and arterial capillary compartments. These results indicate the possible role of a microvascular defect in the pathogenesis of osteoporosis and aplastic anemia
Theory of exciton-exciton correlation in nonlinear optical response
We present a systematic theory of Coulomb interaction effects in the
nonlinear optical processes in semiconductors using a perturbation series in
the exciting laser field. The third-order dynamical response consists of
phase-space filling correction, mean-field exciton-exciton interaction, and
two-exciton correlation effects expressed as a force-force correlation
function. The theory provides a unified description of effects of bound and
unbound biexcitons, including memory-effects beyond the Markovian
approximation. Approximations for the correlation function are presented.Comment: RevTex, 35 pages, 10 PostScript figs, shorter version submitted to
Physical Review
Stabilizing distinguishable qubits against spontaneous decay by detected-jump correcting quantum codes
A new class of error-correcting quantum codes is introduced capable of
stabilizing qubits against spontaneous decay arising from couplings to
statistically independent reservoirs. These quantum codes are based on the idea
of using an embedded quantum code and exploiting the classical information
available about which qubit has been affected by the environment. They are
immediately relevant for quantum computation and information processing using
arrays of trapped ions or nuclear spins. Interesting relations between these
quantum codes and basic notions of design theory are established
Magnetotransport in Two-Dimensional Electron Systems with Spin-Orbit Interaction
We present magnetotransport calculations for homogeneous two-dimensional
electron systems including the Rashba spin-orbit interaction, which mixes the
spin-eigenstates and leads to a modified fan-chart with crossing Landau levels.
The quantum mechanical Kubo formula is evaluated by taking into account
spin-conserving scatterers in an extension of the self-consistent Born
approximation that considers the spin degree of freedom. The calculated
conductivity exhibits besides the well-known beating in the Shubnikov-de Haas
(SdH) oscillations a modulation which is due to a suppression of scattering
away from the crossing points of Landau levels and does not show up in the
density of states. This modulation, surviving even at elevated temperatures
when the SdH oscillations are damped out, could serve to identify spin-orbit
coupling in magnetotransport experiments. Our magnetotransport calculations are
extended also to lateral superlattices and predictions are made with respect to
1/B periodic oscillations in dependence on carrier density and strength of the
spin-orbit coupling.Comment: 8 pages including 8 figures; submitted to PR
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