1,717 research outputs found
The present rate of Supernovae
We present and discuss the most recent determination of the rate of
Supernovae in the local Universe. A comparison with other results shows a
general agreement on the gross values but still significant differences on the
values of the rates of various SN rates in different kinds of galaxies. The
rate of SNe, used as a probe of Star Formation, confirms the young progenitor
scenario for SNII+Ib/c. The increasing diversity of SNe reflects also in the SN
yields which may affect the chemical evolution of the Galaxy but, because of
the limited statistics, we cannot estimate the contributions of the new
subtypes yet. It is also expected that in a few years observational
determinations of the SN rates at various look-back times will be available.Comment: 9 pages, Latex, 1 figure, To appear in the proceedings of the
conference "The Chemical Evolution of The Milky Way: Stars versus Clusters",
eds. F. Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 199
Superfluids, Fluctuations and Disorder
We present a field-theory description of ultracold bosonic atoms in presence
of a disordered external potential. By means of functional integration
techniques, we aim to investigate and review the interplay between disordered
energy landscapes and fluctuations, both thermal and quantum ones. Within the
broken-symmetry phase, up to the Gaussian level of approximation, the disorder
contribution crucially modifies both the condensate depletion and the
superfluid response. Remarkably, it is found that the ordered (i.e. superfluid)
phase can be destroyed also in regimes where the random external potential is
suitable for a perturbative analysis. We analyze the simplest case of quenched
disorder and then we move to present the implementation of the replica trick
for ultracold bosonic systems. In both cases, we discuss strengths and
limitations of the reviewed approach, paying specific attention to possible
extensions and the most recent experimental outputs.Comment: 18 pages, 1 figures. Accepted as a Review for the special issue
"Quantum Optics for Fundamental Quantum Mechanics" in Applied Science
Telecom photon interface of solid-state quantum nodes
Solid-state spins such as nitrogen-vacancy (NV) center are promising
platforms for large-scale quantum networks. Despite the optical interface of NV
center system, however, the significant attenuation of its zero-phonon-line
photon in optical fiber prevents the network extended to long distances.
Therefore a telecom-wavelength photon interface would be essential to reduce
the photon loss in transporting quantum information. Here we propose an
efficient scheme for coupling telecom photon to NV center ensembles mediated by
rare-earth doped crystal. Specifically, we proposed protocols for high fidelity
quantum state transfer and entanglement generation with parameters within reach
of current technologies. Such an interface would bring new insights into future
implementations of long-range quantum network with NV centers in diamond acting
as quantum nodes.Comment: 10 pages, 5 figure
Thermal field theory of bosonic gases with finite-range effective interaction
We study a dilute and ultracold Bose gas of interacting atoms by using an
effective field theory which takes account finite-range effects of the
inter-atomic potential. Within the formalism of functional integration from the
grand canonical partition function we derive beyond-mean-field analytical
results which depend on both scattering length and effective range of the
interaction. In particular, we calculate the equation of state of the bosonic
system as a function of these interaction parameters both at zero and finite
temperature including one-loop Gaussian fluctuation. In the case of zero-range
effective interaction we explicitly show that, due to quantum fluctuations, the
bosonic system is thermodynamically stable only for very small values of the
gas parameter. We find that a positive effective range above a critical
threshold is necessary to remove the thermodynamical instability of the uniform
configuration. Remarkably, also for relatively large values of the gas
parameter, our finite-range results are in quite good agreement with recent
zero-temperature Monte Carlo calculations obtained with hard-sphere bosons.Comment: 6 pages, 2 figures, added some equation
Shift of the critical temperature in superconductors: a self-consistent approach
Within the Ginzburg-Landau functional framework for the superconducting
transition, we analyze the fluctuation-driven shift of the critical
temperature. In addition to the order parameter fluctuations, we also take into
account the fluctuations of the vector potential above its vacuum. We detail
the approximation scheme to include the fluctuating fields contribution, based
on the Hartree-Fock-Bogoliubov-Popov framework. We give explicit results for
and spatial dimensions, in terms of easily accessible experimental
parameters such as the Ginzburg-Levanyuk number , which is
related to the width of the critical region where fluctuations cannot be
neglected, and the Ginzburg-Landau parameter , defined as the ratio
between the magnetic penetration length and the coherence one.Comment: 12 pages, 2 figures. Layout issue with Fig. 1 fixed. Editorially
accepted for publication in Scientific Report
Mixed-state quantum transport in correlated spin networks
Quantum spin networks can be used to transport information between separated
registers in a quantum information processor. To find a practical
implementation, the strict requirements of ideal models for perfect state
transfer need to be relaxed, allowing for complex coupling topologies and
general initial states. Here we analyze transport in complex quantum spin
networks in the maximally mixed state and derive explicit conditions that
should be satisfied by propagators for perfect state transport. Using a
description of the transport process as a quantum walk over the network, we
show that it is necessary to phase correlate the transport processes occurring
along all the possible paths in the network. We provide a Hamiltonian that
achieves this correlation, and use it in a constructive method to derive
engineered couplings for perfect transport in complicated network topologies
Finite-Range Corrections to the Thermodynamics of the One-Dimensional Bose Gas
The Lieb-Liniger equation of state accurately describes the zero-temperature
universal properties of a dilute one-dimensional Bose gas in terms of the
s-wave scattering length. For weakly-interacting bosons we derive non-universal
corrections to this equation of state taking into account finite-range effects
of the inter-atomic potential. Within the finite-temperature formalism of
functional integration we find a beyond-mean-field equation of state which
depends on scattering length and effective range of the interaction potential.
Our analytical results, which are obtained performing dimensional
regularization of divergent zero-point quantum fluctuations, show that for the
one-dimensional Bose gas thermodynamic quantities like pressure and sound
velocity are modified by changing the ratio between the effective range and the
scattering length.Comment: 6 pages, 2 figures, accepted for publication in Physical Review
Experimentally efficient methods for estimating the performance of quantum measurements
Efficient methods for characterizing the performance of quantum measurements
are important in the experimental quantum sciences. Ideally, one requires both
a physically relevant distinguishability measure between measurement operations
and a well-defined experimental procedure for estimating the distinguishability
measure. Here, we propose the average measurement fidelity and error between
quantum measurements as distinguishability measures. We present protocols for
obtaining bounds on these quantities that are both estimable using
experimentally accessible quantities and scalable in the size of the quantum
system. We explain why the bounds should be valid in large generality and
illustrate the method via numerical examples.Comment: 20 pages, 1 figure. Expanded details and typos corrected. Accepted
versio
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