6,196 research outputs found
Time Averaged Quantum Dynamics and the Validity of the Effective Hamiltonian Model
We develop a technique for finding the dynamical evolution in time of an
averaged density matrix. The result is an equation of evolution that includes
an Effective Hamiltonian, as well as decoherence terms in Lindblad form.
Applying the general equation to harmonic Hamiltonians, we confirm a previous
formula for the Effective Hamiltonian together with a new decoherence term
which should in general be included, and whose vanishing provides the criteria
for validity of the Effective Hamiltonian approach. Finally, we apply the
theory to examples of the AC Stark Shift and Three- Level Raman Transitions,
recovering a new decoherence effect in the latter.Comment: 7 pages, 2 figure
Asymmetric double-well potential for single atom interferometry
We consider the evolution of a single-atom wavefunction in a time-dependent
double-well interferometer in the presence of a spatially asymmetric potential.
We examine a case where a single trapping potential is split into an asymmetric
double well and then recombined again. The interferometer involves a
measurement of the first excited state population as a sensitive measure of the
asymmetric potential. Based on a two-mode approximation a Bloch vector model
provides a simple and satisfactory description of the dynamical evolution. We
discuss the roles of adiabaticity and asymmetry in the double-well
interferometer. The Bloch model allows us to account for the effects of
asymmetry on the excited state population throughout the interferometric
process and to choose the appropriate splitting, holding and recombination
periods in order to maximize the output signal. We also compare the outcomes of
the Bloch vector model with the results of numerical simulations of the
multi-state time-dependent Schroedinger equation.Comment: 9 pages, 6 figure
Resonant excitonic emission of a single quantum dot in the Rabi regime
We report on coherent resonant emission of the fundamental exciton state in a
single semiconductor GaAs quantum dot. Resonant regime with picoseconde laser
excitation is realized by embedding the quantum dots in a waveguiding
structure. As the pulse intensity is increased, Rabi oscillation is observed up
to three periods. The Rabi regime is achieved owing to an enhanced light-matter
coupling in the waveguide. This is due to a \emph{slow light effect}
(), occuring when an intense resonant pulse propagates in a
medium. The resonant control of the quantum dot fundamental transition opens
new possibilities in quantum state manipulation and quantum optics experiments
in condensed matter physics.Comment: Submitted to Phys. Rev. Let
Resistivity of a Metal between the Boltzmann Transport Regime and the Anderson Transition
We study the transport properties of a finite three dimensional disordered
conductor, for both weak and strong scattering on impurities, employing the
real-space Green function technique and related Landauer-type formula. The
dirty metal is described by a nearest neighbor tight-binding Hamiltonian with a
single s-orbital per site and random on-site potential (Anderson model). We
compute exactly the zero-temperature conductance of a finite size sample placed
between two semi-infinite disorder-free leads. The resistivity is found from
the coefficient of linear scaling of the disorder averaged resistance with
sample length. This ``quantum'' resistivity is compared to the semiclassical
Boltzmann expression computed in both Born approximation and multiple
scattering approximation.Comment: 5 pages, 3 embedded EPS figure
A multiple-scattering approach to interatomic interactions and superradiance in inhomogeneous dielectrics
The dynamics of a collection of resonant atoms embedded inside an
inhomogeneous nondispersive and lossless dielectric is described with a dipole
Hamiltonian that is based on a canonical quantization theory. The dielectric is
described macroscopically by a position-dependent dielectric function and the
atoms as microscopic harmonic oscillators. We identify and discuss the role of
several types of Green tensors that describe the spatio-temporal propagation of
field operators. After integrating out the atomic degrees of freedom, a
multiple-scattering formalism emerges in which an exact Lippmann-Schwinger
equation for the electric field operator plays a central role. The equation
describes atoms as point sources and point scatterers for light. First,
single-atom properties are calculated such as position-dependent
spontaneous-emission rates as well as differential cross sections for elastic
scattering and for resonance fluorescence. Secondly, multi-atom processes are
studied. It is shown that the medium modifies both the resonant and the static
parts of the dipole-dipole interactions. These interatomic interactions may
cause the atoms to scatter and emit light cooperatively. Unlike in free space,
differences in position-dependent emission rates and radiative line shifts
influence cooperative decay in the dielectric. As a generic example, it is
shown that near a partially reflecting plane there is a sharp transition from
two-atom superradiance to single-atom emission as the atomic positions are
varied.Comment: 18 pages, 4 figures, to appear in Physical Review
Inelastic X-ray Scattering by Electronic Excitations in Solids at High Pressure
Investigating electronic structure and excitations under extreme conditions
gives access to a rich variety of phenomena. High pressure typically induces
behavior such as magnetic collapse and the insulator-metal transition in 3d
transition metals compounds, valence fluctuations or Kondo-like characteristics
in -electron systems, and coordination and bonding changes in molecular
solids and glasses. This article reviews research concerning electronic
excitations in materials under extreme conditions using inelastic x-ray
scattering (IXS). IXS is a spectroscopic probe of choice for this study because
of its chemical and orbital selectivity and the richness of information it
provides. Being an all-photon technique, IXS has a penetration depth compatible
with high pressure requirements. Electronic transitions under pressure in 3d
transition metals compounds and -electron systems, most of them strongly
correlated, are reviewed. Implications for geophysics are mentioned. Since the
incident X-ray energy can easily be tuned to absorption edges, resonant IXS,
often employed, is discussed at length. Finally studies involving local
structure changes and electronic transitions under pressure in materials
containing light elements are briefly reviewed.Comment: submitted to Rev. Mod. Phy
Transport and deposition of ocean-sourced microplastic particles by a North Atlantic hurricane
The atmosphere can transport large quantities of microplastics and disperse them throughout the globe to locations inaccessible by many other transport mechanisms. Meteorological events have been proven to pick up and transport particulate matter, however, how they influence the transport and deposition of atmospheric microplastics is still poorly understood. Here we present samples of atmospheric fallout collected during Hurricane Larry as it passed over Newfoundland, Canada in September 2021. During the storm peak, 1.13 × 105 particles m−2 day−1 were deposited, with a decline in deposition after the storm passed. Back-trajectory modelling and polymer type analysis indicate that those microplastics may have been ocean-sourced as the hurricane traversed the garbage patch of the North Atlantic Gyre. This study identifies the influence of North Atlantic hurricanes on the atmospheric transport and deposition of ocean-sourced microplastics and the possible consequences of increased exposure to microplastics in remote areas
Cavity losses for the dissipative Jaynes-Cummings Hamiltonian beyond Rotating Wave Approximation
A microscopic derivation of the master equation for the
Jaynes-Cummings model with cavity losses is given, taking into account the
terms in the dissipator which vary with frequencies of the order of the vacuum
Rabi frequency. Our approach allows to single out physical contexts wherein the
usual phenomenological dissipator turns out to be fully justified and
constitutes an extension of our previous analysis [Scala M. {\em et al.} 2007
Phys. Rev. A {\bf 75}, 013811], where a microscopic derivation was given in the
framework of the Rotating Wave Approximation.Comment: 12 pages, 1 figur
Strong electron-photon coupling in one-dimensional quantum dot chain: Rabi waves and Rabi wavepackets
We predict and theoretically investigate the new coherent effect of nonlinear
quantum optics -- spatial propagation of Rabi oscillations (Rabi waves) in
one-dimensional quantum dot (QD) chain. QD-chain is modeled by the set of
two-level quantum systems with tunnel coupling between neighboring QDs. The
space propagation of Rabi waves in the form of traveling waves and wave packets
is considered. It is shown, that traveling Rabi waves are quantum states of
QD-chain dressed by radiation. The dispersion characteristics of traveling Rabi
waves are investigated and their dependence on average number of photons in
wave is demonstrated. The propagation of Rabi wave packets is accompanied by
the transfer of the inversion and quantum correlations along the QD-chain and
by the transformation of quantum light statistics. The conditions of
experimental observability are analyzed. The effect can find practical use in
quantum computing and quantum informatics.Comment: 16 pages, 15 figure
Hyperfine Coherence in the Presence of Spontaneous Photon Scattering
The coherence of a hyperfine-state superposition of a trapped Be
ion in the presence of off-resonant light is experimentally studied. It is
shown that Rayleigh elastic scattering of photons that does not change state
populations also does not affect coherence. Coherence times exceeding the
average scattering time of 19 photons are observed. This result implies that,
with sufficient control over its parameters, laser light can be used to
manipulate hyperfine-state superpositions with very little decoherence.Comment: Letter, 4 figure
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