10,777 research outputs found
Avoided level crossing spectroscopy with dressed matter waves
We devise a method for probing resonances of macroscopic matter waves in
shaken optical lattices by monitoring their response to slow parameter changes,
and show that such resonances can be disabled by particular choices of the
driving amplitude. The theoretical analysis of this scheme reveals far-reaching
analogies between dressed atoms and time-periodically forced matter waves.Comment: 4 pages, 3 figure
Process chain approach to high-order perturbation calculus for quantum lattice models
A method based on Rayleigh-Schroedinger perturbation theory is developed that
allows to obtain high-order series expansions for ground-state properties of
quantum lattice models. The approach is capable of treating both lattice
geometries of large spatial dimensionalities d and on-site degrees of freedom
with large state space dimensionalities. It has recently been used to
accurately compute the zero-temperature phase diagram of the Bose-Hubbard model
on a hypercubic lattice, up to arbitrary large filling and for d=2, 3 and
greater [Teichmann et al., Phys. Rev. B 79, 100503(R) (2009)].Comment: 11 pages, 6 figure
Atomic quantum gases in periodically driven optical lattices
Time periodic forcing in the form of coherent radiation is a standard tool
for the coherent manipulation of small quantum systems like single atoms. In
the last years, periodic driving has more and more also been considered as a
means for the coherent control of many-body systems. In particular, experiments
with ultracold quantum gases in optical lattices subjected to periodic driving
in the lower kilohertz regime have attracted a lot of attention. Milestones
include the observation of dynamic localization, the dynamic control of the
quantum phase transition between a bosonic superfluid and a Mott insulator, as
well as the dynamic creation of strong artificial magnetic fields and
topological band structures. This article reviews these recent experiments and
their theoretical description. Moreover, fundamental properties of periodically
driven many-body systems are discussed within the framework of Floquet theory,
including heating, relaxation dynamics, anomalous topological edge states, and
the response to slow parameter variations.Comment: Review, accepted for publication as Colloquium in Reviews of Modern
Physic
Does Signaling Work in Markets for Information Services? An Empirical Investigation for Insurance Intermediaries in Germany
Insurance intermediation services are information services which exhibit strong information asymmetries. We empirically analyze whether signaling works in the German market for insurance intermediation services. For this a signal must increase service quality and be easily identifiable by consumers so that it pays for intermediaries to spend the related costs. By using OLS and logit estimations we test whether intermediary type, reputational activities and a variety of signaling instruments work as credible signals. Our findings confirm the main hypotheses derived from signaling theory as to the poor working of market forces in markets for information services. Accordingly, public policy regulation is necessary to mitigate the resulting problems.signaling, insurance intermediation, information services
Interband heating processes in a periodically driven optical lattice
We investigate multi-"photon" interband excitation processes in an optical
lattice that is driven periodically in time by a modulation of the lattice
depth. Assuming the system to be prepared in the lowest band, we compute the
excitation spectrum numerically. Moreover, we estimate the effective coupling
parameters for resonant interband excitation processes analytically, employing
degenerate perturbation theory in Floquet space. We find that below a threshold
driving strength, interband excitations are suppressed exponentially with
respect to the inverse driving frequency. For sufficiently low frequencies,
this leads to a rather sudden onset of interband heating, once the driving
strength reaches the threshold. We argue that this behavior is rather generic
and should also be found in lattice systems that are driven by other forms of
periodic forcing. Our results are relevant for Floquet engineering, where a
lattice system is driven periodically in time in order to endow it with novel
properties like the emergence of a strong artificial magnetic field or a
topological band structure. In this context, interband excitation processes
correspond to detrimental heating.Comment: 11 pages, 4 figure
High-frequency approximation for periodically driven quantum systems from a Floquet-space perspective
We derive a systematic high-frequency expansion for the effective Hamiltonian
and the micromotion operator of periodically driven quantum systems. Our
approach is based on the block diagonalization of the quasienergy operator in
the extended Floquet Hilbert space by means of degenerate perturbation theory.
The final results are equivalent to those obtained within a different approach
[Phys.\ Rev.\ A {\bf 68}, 013820 (2003), Phys.\ Rev.\ X {\bf 4}, 031027 (2014)]
and can also be related to the Floquet-Magnus expansion [J.\ Phys.\ A {\bf 34},
3379 (2000)]. We discuss that the dependence on the driving phase, which
plagues the latter, can lead to artifactual symmetry breaking. The
high-frequency approach is illustrated using the example of a periodically
driven Hubbard model. Moreover, we discuss the nature of the approximation and
its limitations for systems of many interacting particles.Comment: 48 pages, 7 figure
The Quality of Insurance Intermediary Services - An Analysis of Conduct and Performance in the German Market of Insurance Intermediation
Based on a sample of 946 German insurance intermediaries, the factors that affect the quality of the information services provided by them are studied using OLS-estimations. Applying a search theoretical approach, we analyze the impact of supply and demand side variables on service quality. Besides, the working of signaling devices (like reputation, advertising or certificates) to reduce asymmetric information with respect to the service quality of insurance intermediaries is examined. The results obtained support the main hypotheses derived from industrial organization theories as to the poor working of quality competition under incomplete and asymmetric information on the side of consumers. Thus, public policy should concentrate on increasing transparency about intermediaries' (in-)dependence from insurance companies and improve consumers' financial literacy to raise the overall quality of the information services provided by insurance intermediaries.Performance of Insurance Distribution Systems, Information Quality
Point patterns occurring on complex structures in space and space-time: An alternative network approach
This paper presents an alternative approach of analyzing possibly multitype
point patterns in space and space-time that occur on network structures, and
introduces several different graph-related intensity measures. The proposed
formalism allows to control for processes on undirected, directional as well as
partially directed network structures and is not restricted to linearity or
circularity
Orbital-driven melting of a bosonic Mott insulator in a shaken optical lattice
In order to study the interplay between localized and dispersive orbital
states in a system of ultracold atoms in an optical lattice, we investigate the
possibility to coherently couple the lowest two Bloch bands by means of
resonant periodic forcing. Considering bosons in one dimension, it is shown
that a strongly interacting Floquet system can be realized, where at every
lattice site two (and only two) near-degenerate orbital states are relevant. By
smoothly tuning both states into resonance we find that the system can undergo
an orbital-driven Mott-insulator-to-superfluid transition. As an intriguing
consequence of the kinetic frustration in the system, this transition can be
either continuous or first-order, depending on parameters such as lattice depth
and filling.Comment: 7 pages, 3 figure
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