18,215 research outputs found
Classical and quantum interference in multiband optical Bloch oscillations
Classical and quantum interference of light propagating in arrays of coupled
waveguides and undergoing multiband optical Bloch oscillations (BOs) with
negligible Zener tunneling is theoretically investigated. In particular, it is
shown that Mach-Zehnder-like interference effects spontaneously arise in
multiband BOs owing to beam splitting and subsequent beam recombination
occurring in one BO cycle. As a noteworthy example of quantum interference, we
discuss the doubling of interference fringes in photon counting rates for a
correlated photon pair undergoing two-band BOs, a phenomenon analogous to the
manifestation of the de Broglie wavelength of an entangled biphoton state
observed in quantum Mach-Zehnder interferometry.Comment: 11 pages, 4 figure
Method and apparatus for fabricating improved solar cell modules
A method and apparatus for fabricating an improved solar cell module is described. The apparatus includes a supply drum for feeding a flexible strip having etched electrical circuitry deposited on it a supply drum for feeding into overlying engagement with the flexible strip a flexible tape having a pair of exposed tacky surfaces, and a plurality of rams for receiving and depositing a plurality of solar cells in side-by-side relation on an exposed tacky surface of the tape in electrical contacting engagement with the etched circuitry
The Kohn-Luttinger Effect in Gauge Theories
Kohn and Luttinger showed that a many body system of fermions interacting via
short range forces becomes superfluid even if the interaction is repulsive in
all partial waves. In gauge theories such as QCD the interaction between
fermions is long range and the assumptions of Kohn and Luttinger are not
satisfied. We show that in a U(1) gauge theory the Kohn-Luttinger phenomenon
does not take place. In QCD attractive channels always exist, but there are
cases in which the primary pairing channel leaves some fermions ungapped. As an
example we consider the unpaired fermion in the 2SC phase of QCD with two
flavors. We show that it acquires a very small gap via a mechanism analogous to
the Kohn-Luttinger effect. The gap is too small to be phenomenologically
relevant.Comment: 5 pages, 2 figure, minor revisions, to appear in PR
Experimental status of the isoscalar S wave at low energy: pole and scattering length
The experimental results obtained in the last few years on kaon decays
(K and, above all, Ke4 decays) allow a reliable, model independent
determination of low energy scattering in the S0 wave. Using them and,
eventually, other sets of data, it is possible to give a precise
parametrization of the S0 wave as well as to find the scattering length and
effective range parameter. One can also perform an extrapolation to the pole of
the " resonance" []. We obtain the results
and, for the pole, M_\sigma=484\pm17 \mev,\quad\gammav_\sigma/2=
255\pm10 {\rm MeV}.Comment: Plain TeX;4 figures; improved data used; version to appear in Phys.
Rev.
Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains
Elementary particles such as the electron carry several quantum numbers, for
example, charge and spin. However, in an ensemble of strongly interacting
particles, the emerging degrees of freedom can fundamentally differ from those
of the individual constituents. Paradigmatic examples of this phenomenon are
one-dimensional systems described by independent quasiparticles carrying either
spin (spinon) or charge (holon). Here we report on the dynamical deconfinement
of spin and charge excitations in real space following the removal of a
particle in Fermi-Hubbard chains of ultracold atoms. Using space- and
time-resolved quantum gas microscopy, we track the evolution of the excitations
through their signatures in spin and charge correlations. By evaluating
multi-point correlators, we quantify the spatial separation of the excitations
in the context of fractionalization into single spinons and holons at finite
temperatures
Strategic Network Formation with Attack and Immunization
Strategic network formation arises where agents receive benefit from
connections to other agents, but also incur costs for forming links. We
consider a new network formation game that incorporates an adversarial attack,
as well as immunization against attack. An agent's benefit is the expected size
of her connected component post-attack, and agents may also choose to immunize
themselves from attack at some additional cost. Our framework is a stylized
model of settings where reachability rather than centrality is the primary
concern and vertices vulnerable to attacks may reduce risk via costly measures.
In the reachability benefit model without attack or immunization, the set of
equilibria is the empty graph and any tree. The introduction of attack and
immunization changes the game dramatically; new equilibrium topologies emerge,
some more sparse and some more dense than trees. We show that, under a mild
assumption on the adversary, every equilibrium network with agents contains
at most edges for . So despite permitting topologies denser
than trees, the amount of overbuilding is limited. We also show that attack and
immunization don't significantly erode social welfare: every non-trivial
equilibrium with respect to several adversaries has welfare at least as that of
any equilibrium in the attack-free model.
We complement our theory with simulations demonstrating fast convergence of a
new bounded rationality dynamic which generalizes linkstable best response but
is considerably more powerful in our game. The simulations further elucidate
the wide variety of asymmetric equilibria and demonstrate topological
consequences of the dynamics e.g. heavy-tailed degree distributions. Finally,
we report on a behavioral experiment on our game with over 100 participants,
where despite the complexity of the game, the resulting network was
surprisingly close to equilibrium.Comment: The short version of this paper appears in the proceedings of WINE-1
Electromagnetic energy and energy flows in photonic crystals made of arrays of parallel dielectric cylinders
We consider the electromagnetic propagation in two-dimensional photonic
crystals, formed by parallel dielectric cylinders embedded a uniform medium.
The frequency band structure is computed using the standard plane-wave
expansion method, and the corresponding eigne-modes are obtained subsequently.
The optical flows of the eigen-modes are calculated by a direct computation
approach, and several averaging schemes of the energy current are discussed.
The results are compared to those obtained by the usual approach that employs
the group velocity calculation. We consider both the case in which the
frequency lies within passing band and the situation in which the frequency is
in the range of a partial bandgap. The agreements and discrepancies between
various averaging schemes and the group velocity approach are discussed in
detail. The results indicate the group velocity can be obtained by appropriate
averaging method.Comment: 23 pages, 5 figure
Equivalent bosonic theory for the massive Thirring model with non-local interaction
We study, through path-integral methods, an extension of the massive Thirring
model in which the interaction between currents is non-local. By examining the
mass-expansion of the partition function we show that this non-local massive
Thirring model is equivalent to a certain non-local extension of the
sine-Gordon theory. Thus, we establish a non-local generalization of the famous
Coleman's equivalence. We also discuss some possible applications of this
result in the context of one-dimensional strongly correlated systems and
finite-size Quantum Field Theories.Comment: 15 pages, latex, no figure
Level crossings in a cavity QED model
In this paper I study the dynamics of a two-level atom interacting with a
standing wave field. When the atom is subjected to a weak linear force, the
problem can be turned into a time dependent one, and the evolution is
understood from the band structure of the spectrum. The presence of level
crossings in the spectrum gives rise to Bloch oscillations of the atomic
motion. Here I investigate the effects of the atom-field detuning parameter. A
variety of different level crossings are obtained by changing the magnitude of
the detuning, and the behaviour of the atomic motion is strongly affected due
to this. I also consider the situation in which the detuning is oscillating in
time and its impact on the atomic motion. Wave packet simulations of the full
problem are treated numerically and the results are compared with analytical
solutions given by the standard Landau-Zener and the three-level Landau-Zener
models.Comment: 12 pages, 10 figure
Test of a Jastrow-type wavefunction for a trapped few-body system in one dimension
For a system with interacting quantum mechanical particles in a
one-dimensional harmonic oscillator, a trial wavefunction with simple structure
based on the solution of the corresponding two-particle system is suggested and
tested numerically. With the inclusion of a scaling parameter for the distance
between particles, at least for the very small systems tested here the ansatz
gives a very good estimate of the ground state energy, with the error being of
the order of ~1% of the gap to the first excited state
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