7,148 research outputs found
A new correlator in quantum spin chains
We propose a new correlator in one-dimensional quantum spin chains, the
Emptiness Formation Probability (EFP). This is a natural generalization
of the Emptiness Formation Probability (EFP), which is the probability that the
first spins of the chain are all aligned downwards. In the EFP we let
the spins in question be separated by sites. The usual EFP corresponds to
the special case when , and taking allows us to quantify non-local
correlations. We express the EFP for the anisotropic XY model in a
transverse magnetic field, a system with both critical and non-critical
regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find
that the magnetic field induces an interesting length scale.Comment: 6 pages, 1 figur
Full counting statistics of chaotic cavities with many open channels
Explicit formulas are obtained for all moments and for all cumulants of the
electric current through a quantum chaotic cavity attached to two ideal leads,
thus providing the full counting statistics for this type of system. The
approach is based on random matrix theory, and is valid in the limit when both
leads have many open channels. For an arbitrary number of open channels we
present the third cumulant and an example of non-linear statistics.Comment: 4 pages, no figures; v2-added references; typos correcte
Semiclassical treatment of quantum chaotic transport with a tunnel barrier
We consider the problem of a semiclassical description of quantum chaotic
transport, when a tunnel barrier is present in one of the leads. Using a
semiclassical approach formulated in terms of a matrix model, we obtain
transport moments as power series in the reflection probability of the barrier,
whose coefficients are rational functions of the number of open channels M. Our
results are therefore valid in the quantum regime and not only when .
The expressions we arrive at are not identical with the corresponding
predictions from random matrix theory, but are in fact much simpler. Both
theories agree as far as we can test.Comment: 17 pages, 5 figure
The dipole anisotropy of WISE x SuperCOSMOS number counts
We probe the isotropy of the Universe with the largest all-sky photometric
redshift dataset currently available, namely WISE~~SuperCOSMOS. We
search for dipole anisotropy of galaxy number counts in multiple redshift
shells within the range, for two subsamples drawn from the
same parent catalogue. Our results show that the dipole directions are in good
agreement with most of the previous analyses in the literature, and in most
redshift bins the dipole amplitudes are well consistent with CDM-based
mocks in the cleanest sample of this catalogue. In the range, however,
we obtain a persistently large anisotropy in both subsamples of our dataset.
Overall, we report no significant evidence against the isotropy assumption in
this catalogue except for the lowest redshift ranges. The origin of the latter
discrepancy is unclear, and improved data may be needed to explain it.Comment: 5 pages, 4 figures, 2 tables. Published in MNRA
Exponentially small quantum correction to conductance
When time-reversal symmetry is broken, the average conductance through a
chaotic cavity, from an entrance lead with open channels to an exit lead
with open channels, is given by , where . We show
that, when tunnel barriers of reflectivity are placed on the leads,
two correction terms appear in the average conductance, and that one of them is
proportional to . Since , this correction is
exponentially small in the semiclassical limit. Surprisingly, we derive this
term from a semiclassical approximation, generally expected to give only
leading orders in powers of . Even though the theory is built
perturbatively both in and in , the final result is exact.Comment: 9 pages, 2 figure
Fetal aorto-pulmonary window: case series and review of the literature
Aorto-pulmonary window is a rare congenital cardiac anomaly characterized by a communication between the aorta and the pulmonary artery above the semilunar valves. Prenatal diagnosis is rare. We report four fetuses with aorto-pulmonary window and review the relevant literature. Approximately half of the reported cases had additional cardiac defects; none had chromosomal abnormalities. In cases with normal cardiac connections, the diagnosis can be made prenatally on the standard three–vessel view as seen in two of our cases. In one fetus with complete transposition, the diagnosis was made retrospectively on sagittal views. In the remaining case the window was seen post-natally but could not be identified retrospectively due to the abnormal supero-inferior relationship of the ventricles and vessels
Statistics of quantum transport in chaotic cavities with broken time-reversal symmetry
The statistical properties of quantum transport through a chaotic cavity are
encoded in the traces \T={\rm Tr}(tt^\dag)^n, where is the transmission
matrix. Within the Random Matrix Theory approach, these traces are random
variables whose probability distribution depends on the symmetries of the
system. For the case of broken time-reversal symmetry, we present explicit
closed expressions for the average value and for the variance of \T for all
. In particular, this provides the charge cumulants \Q of all orders. We
also compute the moments of the conductance . All the
results obtained are exact, {\it i.e.} they are valid for arbitrary numbers of
open channels.Comment: 5 pages, 4 figures. v2-minor change
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