241 research outputs found
DC field induced enhancement and inhibition of spontaneous emission in a cavity
We demonstrate how spontaneous emission in a cavity can be controlled by the
application of a dc field. The method is specially suitable for Rydberg atoms.
We present a simple argument for the control of emission.Comment: 3-pages, 2figure. accepted in Phys. Rev.
Non-Markovian Dynamics of Entanglement for Multipartite Systems
Entanglement dynamics for a couple of two-level atoms interacting with
independent structured reservoirs is studied using a non-perturbative approach.
It is shown that the revival of atom entanglement is not necessarily
accompanied by the sudden death of reservoir entanglement, and vice versa. In
fact, atom entanglement can revive before, simultaneously or even after the
disentanglement of reservoirs. Using a novel method based on the population
analysis for the excited atomic state, we present the quantitative criteria for
the revival and death phenomena. For giving a more physically intuitive
insight, the quasimode Hamiltonian method is applied. Our quantitative analysis
is helpful for the practical engineering of entanglement.Comment: 10 pages and 4 figure
Multi-Modal Properties and Dynamics of the Gradient Echo Quantum Memory
We investigate the properties of a recently proposed Gradient Echo Memory
(GEM) scheme for information mapping between optical and atomic systems. We
show that GEM can be described by the dynamic formation of polaritons in
k-space. This picture highlights the flexibility and robustness with regards to
the external control of the storage process. Our results also show that, as GEM
is a frequency-encoding memory, it can accurately preserve the shape of signals
that have large time-bandwidth products, even at moderate optical depths. At
higher optical depths, we show that GEM is a high fidelity multi-mode quantum
memory.Comment: 4 pages 3 figure
Jacobi Identity for Vertex Algebras in Higher Dimensions
Vertex algebras in higher dimensions provide an algebraic framework for
investigating axiomatic quantum field theory with global conformal invariance.
We develop further the theory of such vertex algebras by introducing formal
calculus techniques and investigating the notion of polylocal fields. We derive
a Jacobi identity which together with the vacuum axiom can be taken as an
equivalent definition of vertex algebra.Comment: 35 pages, references adde
Scaling properties of cavity-enhanced atom cooling
We extend an earlier semiclassical model to describe the dissipative motion
of N atoms coupled to M modes inside a coherently driven high-finesse cavity.
The description includes momentum diffusion via spontaneous emission and cavity
decay. Simple analytical formulas for the steady-state temperature and the
cooling time for a single atom are derived and show surprisingly good agreement
with direct stochastic simulations of the semiclassical equations for N atoms
with properly scaled parameters. A thorough comparison with standard free-space
Doppler cooling is performed and yields a lower temperature and a cooling time
enhancement by a factor of M times the square of the ratio of the atom-field
coupling constant to the cavity decay rate. Finally it is shown that laser
cooling with negligible spontaneous emission should indeed be possible,
especially for relatively light particles in a strongly coupled field
configuration.Comment: 7 pages, 5 figure
Electromagnetic Field Induced Modification of Branching Ratios for Emission in Structured Vacuum
We report a fundamental effect of the electromagnetic field induced
modification of the branching ratios for emission into several final states.
The modifications are especially significant if the vacuum into which the atom
is radiating has a finite spectral width comparable with the separation of the
final states. This is easily realizable in cavity QED. Further our results are
quite generic and are applicable to any system interacting with a structured
reservoir.Comment: 7 pages, 6 figures, Submitted to New Journal of Physic
Snow information is required in subcontinental scale predictions of mountain plant distributions
Aim To examine how snow cover and permafrost affect plant species distributions at a subcontinental extent. Location Mountain realm of Fennoscandia, northern Europe. Time period Species data from 1 January 1990-25 February 2019. Major taxa studied Arctic-alpine and boreal vascular plants. Methods We examined the effect of snow persistence and permafrost occurrence on the distributions of arctic-alpine and boreal plant species while controlling for climate, topography and geological factors. Data comprised 475,811 observations from 671 species in the Fennoscandian mountains. We investigated the relationships between species distributions and environmental variables using four modelling methods and ensemble modelling building on both non-spatial and spatial models. Results Snow persistence was the most important driver of plant species distributions, with the greatest variable importance for both arctic-alpine (38.2%) and boreal (49.9%) species. Permafrost had a consistent minor effect on the predicted distributions. Arctic-alpine plants occur in areas with long snow persistence and permafrost, whereas boreal species showed the opposite habitat preferences. Main conclusions Our results highlight the importance of snow persistence in driving the distribution of vascular plant species in cold environments at a subcontinental scale. The notable contribution of the cryosphere to plant species distribution models indicates that the inclusion of snow information in particular may improve our understanding and model predictions of biogeographical patterns in cold regions.Peer reviewe
Inhibition of Decoherence due to Decay in a Continuum
We propose a scheme for slowing down decay into a continuum. We make use of a
sequence of ultrashort -pulses applied on an auxiliary transition of the
system so that there is a destructive interference between the two transition
amplitudes - one before the application of the pulse and the other after the
application of the pulse. We give explicit results for a structured continuum.
Our scheme can also inhibit unwanted transitions.Comment: 11 pages and 4 figures, submitted to Physical Review Letter
Vacuum-stimulated cooling of single atoms in three dimensions
Taming quantum dynamical processes is the key to novel applications of
quantum physics, e.g. in quantum information science. The control of
light-matter interactions at the single-atom and single-photon level can be
achieved in cavity quantum electrodynamics, in particular in the regime of
strong coupling where atom and cavity form a single entity. In the optical
domain, this requires permanent trapping and cooling of an atom in a
micro-cavity. We have now realized three-dimensional cavity cooling and
trapping for an orthogonal arrangement of cooling laser, trap laser and cavity
vacuum. This leads to average single-atom trapping times exceeding 15 seconds,
unprecedented for a strongly coupled atom under permanent observation.Comment: 4 pages, 4 figure
Trapping and cooling single atoms with far-off resonance intracavity doughnut modes
We investigate cooling and trapping of single atoms inside an optical cavity
using a quasi-resonant field and a far-off resonant mode of the Laguerre-Gauss
type. The far-off resonant doughnut mode provides an efficient trapping in the
case when it shifts the atomic internal ground and excited state in the same
way, which is particularly useful for quantum information applications of
cavity quantum electrodynamics (QED) systems. Long trapping times can be
achieved, as shown by full 3-D simulations of the quasi-classical motion inside
the resonator.Comment: 18 pages, 18 figures, RevTe
- âŠ