9,642 research outputs found
Nonequilibrium dynamical mean-field theory for bosonic lattice models
We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium "phase diagrams" which map out the different dynamical
regimes.Comment: 18 pages, 8 figure
Transaction services, inflation, and welfare
This paper is motivated by empirical observations on the comovements of currency velocity, inflation, and the relative size of the credit services sector. We document these comovements and incorporate into a monetary growth model a credit services sector that provides services that help people economize on money. Our model makes two new contributions. First, we show that direct evidence on the appropriately defined credit service sector for the United States is consistent with the welfare cost measured using an estimated money demand schedule. Second, we provide welfare cost of inflation estimates that have some new features.Inflation (Finance) ; Welfare
Nanoscale Suppression of Magnetization at Atomically Assembled Manganite Interfaces
Using polarized X-rays, we compare the electronic and magnetic properties of
a La(2/3)Sr(1/3)MnO(3)(LSMO)/SrTiO(3)(STO) and a modified
LSMO/LaMnO(3)(LMO)/STO interface. Using the technique of X-ray resonant
magnetic scattering (XRMS), we can probe the interfaces of complicated layered
structures and quantitatively model depth-dependent magnetic profiles as a
function of distance from the interface. Comparisons of the average electronic
and magnetic properties at the interface are made independently using X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The
XAS and the XMCD demonstrate that the electronic and magnetic structure of the
LMO layer at the modified interface is qualitatively equivalent to the
underlying LSMO film. From the temperature dependence of the XMCD, it is found
that the near surface magnetization for both interfaces falls off faster than
the bulk. For all temperatures in the range of 50K - 300K, the magnetic
profiles for both systems always show a ferromagnetic component at the
interface with a significantly suppressed magnetization that evolves to the
bulk value over a length scale of ~1.6 - 2.4 nm. The LSMO/LMO/STO interface
shows a larger ferromagnetic (FM) moment than the LSMO/STO interface, however
the difference is only substantial at low temperature.Comment: 4 pages, 4 figure
From quantum pulse gate to quantum pulse shaper -- enigneered frequency conversion in nonlinear optical waveguides
Full control over the spatio-temporal structure of quantum states of light is
an important goal in quantum optics, to generate for instance single-mode
quantum pulses or to encode information on multiple modes, enhancing channel
capacities. Quantum light pulses feature an inherent, rich spectral
broadband-mode structure. In recent years, exploring the use of integrated
optics as well as source-engineering has led to a deep understanding of the
pulse-mode structure of guided quantum states of light. In addition, several
groups have started to investigate the manipulation of quantum states by means
of single-photon frequency conversion. In this paper we explore new routes
towards complete control of the inherent pulse-modes of ultrafast pulsed
quantum states by employing specifically designed nonlinear waveguides with
adapted dispersion properties. Starting from our recently proposed quantum
pulse gate (QPG) we further generalize the concept of spatio-spectral
engineering for arbitrary \chitwo-based quantum processes. We analyse the
sum-frequency generation based QPG and introduce the difference-frequency
generation based quantum pulse shaper (QPS). Together, these versatile and
robust integrated optics devices allow for arbitrary manipulations of the
pulse-mode structure of ultrafast pulsed quantum states. The QPG can be
utilized to select an arbitrary pulse mode from a multimode input state,
whereas the QPS enables the generation of specific pulse modes from an input
wavepacket with Gaussian-shaped spectrum.Comment: 21 pages, 9 figure
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