3,697 research outputs found
Perfect transfer of multiple excitations in quantum networks
We present a general formalism to the problem of perfect state-transfer
(PST), where the state involves multiple excitations of the quantum network. A
key feature of our formalism is that it allows for inclusion of nontrivial
interactions between the excitations. Hence, it is perfectly suited to
addressing the problem of PST in the context of various types of physical
realizations. The general formalism is also flexible enough to account for
situations where multiple excitations are "focused" onto the same site.Comment: close to the version published in Phys. Rev. A. In version 2, a typo
has been corrected in Sec. III
Communication in quantum networks of logical bus topology
Perfect state transfer (PST) is discussed in the context of passive quantum
networks with logical bus topology, where many logical nodes communicate using
the same shared media, without any external control. The conditions under
which, a number of point-to-point PST links may serve as building blocks for
the design of such multi-node networks are investigated. The implications of
our results are discussed in the context of various Hamiltonians that act on
the entire network, and are capable of providing PST between the logical nodes
of a prescribed set in a deterministic manner.Comment: 9 pages, 1 figur
Solving the m-mixing problem for the three-dimensional time-dependent Schr\"{o}dinger equation by rotations: application to strong-field ionization of H2+
We present a very efficient technique for solving the three-dimensional
time-dependent Schrodinger equation. Our method is applicable to a wide range
of problems where a fullly three-dimensional solution is required, i.e., to
cases where no symmetries exist that reduce the dimensionally of the problem.
Examples include arbitrarily oriented molecules in external fields and atoms
interacting with elliptically polarized light. We demonstrate that even in such
cases, the three-dimensional problem can be decomposed exactly into two
two-dimensional problems at the cost of introducing a trivial rotation
transformation. We supplement the theoretical framework with numerical results
on strong-field ionization of arbitrarily oriented H2+ molecules.Comment: 5 pages, 4 figure
Non-Markovian Decay of a Three Level Cascade Atom in a Structured Reservoir
We present a formalism that enables the study of the non-Markovian dynamics
of a three-level ladder system in a single structured reservoir. The
three-level system is strongly coupled to a bath of reservoir modes and two
quantum excitations of the reservoir are expected. We show that the dynamics
only depends on reservoir structure functions, which are products of the mode
density with the coupling constant squared. This result may enable pseudomode
theory to treat multiple excitations of a structured reservoir. The treatment
uses Laplace transforms and an elimination of variables to obtain a formal
solution. This can be evaluated numerically (with the help of a numerical
inverse Laplace transform) and an example is given. We also compare this result
with the case where the two transitions are coupled to two separate structured
reservoirs (where the example case is also analytically solvable)
A combined R-matrix eigenstate basis set and finite-differences propagation method for the time-dependent Schr\"{od}dinger equation: the one-electron case
In this work we present the theoretical framework for the solution of the
time-dependent Schr\"{o}dinger equation (TDSE) of atomic and molecular systems
under strong electromagnetic fields with the configuration space of the
electron's coordinates separated over two regions, that is regions and
. In region the solution of the TDSE is obtained by an R-matrix basis
set representation of the time-dependent wavefunction. In region a grid
representation of the wavefunction is considered and propagation in space and
time is obtained through the finite-differences method. It appears this is the
first time a combination of basis set and grid methods has been put forward for
tackling multi-region time-dependent problems. In both regions, a high-order
explicit scheme is employed for the time propagation. While, in a purely
hydrogenic system no approximation is involved due to this separation, in
multi-electron systems the validity and the usefulness of the present method
relies on the basic assumption of R-matrix theory, namely that beyond a certain
distance (encompassing region ) a single ejected electron is distinguishable
from the other electrons of the multi-electron system and evolves there (region
II) effectively as a one-electron system. The method is developed in detail for
single active electron systems and applied to the exemplar case of the hydrogen
atom in an intense laser field.Comment: 13 pages, 6 figures, submitte
A novel detrimental homozygous mutation in the WFS1 gene in two sisters from nonconsanguineous parents with untreated diabetes insipidus
Given the limited lifespan and with the recent progress in experimental treatments for WS, timely diagnosis and multidisciplinary treatment for DI/DM, hydronephrosis, and visual/psychiatric status-maintaining quality of life-are of crucial importance
Beyond single-photon localization at the edge of a Photonic Band Gap
We study spontaneous emission in an atomic ladder system, with both
transitions coupled near-resonantly to the edge of a photonic band gap
continuum. The problem is solved through a recently developed technique and
leads to the formation of a ``two-photon+atom'' bound state with fractional
population trapping in both upper states. In the long-time limit, the atom can
be found excited in a superposition of the upper states and a ``direct''
two-photon process coexists with the stepwise one. The sensitivity of the
effect to the particular form of the density of states is also explored.Comment: to appear in Physical Review
ACHINOS: A Multi-Anode Read-Out for Position Reconstruction and Tracking with Spherical Proportional Counters
The spherical proportional counter is a versatile gaseous detector with
physics applications ranging from rare event searches to fast neutron
spectroscopy. In its simplest form, the detector operates with a single channel
read-out, and uses pulse-shape information to reconstruct the interaction
radius, which is used for background discrimination and target volume
definition. Recent developments in the read-out instrumentation have enabled
the use of a multi-anode read-out structure, ACHINOS. The multiple anodes
provide information about the interaction position which, coupled with the
radial information, can be used to reconstruct an ionisation track. This
ability has implications for several applications of the detector, for example,
background discrimination in rare event searches.Comment: 4 pages, 3 figure
Homeless population
The aim was to derive and analyze a model for numbers of homeless and non-homeless people in a borough, in particular to see how these figures might be affected by different policies regarding housing various categories of people. Most attention was focused on steady populations although the stability of these and possible timescales of dynamic problems were also discussed.
The main outcome of this brief study is the identification of the key role played by the constant k_1 - the constant which fixes the speed at which the homeless are rehoused in permanent council property. Reducing this constant, i.e. making the system "fairer" with less priority to accommodating homeless families, appears to have little effect on the sizes of other categories on the waiting list but there is a marked increase in the number of households in temporary accommodation.
The model, indicated by the size of its longest time-scale, should be modified to allow for births etc.
It could be varied by allowing people to remove themselves from the register or by allowing the rates at which registered and unregistered people become homeless to differ, but these modifications are unlikely to substantially change the main result.
The inclusion of movement from the homeless to the general population would have the effect of limiting the numbers in temporary accommodation. However, it is thought this effect is very small so a great reduction in k_1 would be needed for this flow to become significant
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