767 research outputs found
Nano-friction in cavity quantum electrodynamics
The dynamics of cold trapped ions in a high-finesse resonator results from
the interplay between the long-range Coulomb repulsion and the cavity-induced
interactions. The latter are due to multiple scatterings of laser photons
inside the cavity and become relevant when the laser pump is sufficiently
strong to overcome photon decay. We study the stationary states of ions coupled
with a mode of a standing-wave cavity as a function of the cavity and laser
parameters, when the typical length scales of the two self-organizing
processes, Coulomb crystallization and photon-mediated interactions, are
incommensurate. The dynamics are frustrated and in specific limiting cases can
be cast in terms of the Frenkel-Kontorova model, which reproduces features of
friction in one dimension. We numerically recover the sliding and pinned
phases. For strong cavity nonlinearities, they are in general separated by
bistable regions where superlubric and stick-slip dynamics coexist. The cavity,
moreover, acts as a thermal reservoir and can cool the chain vibrations to
temperatures controlled by the cavity parameters and by the ions phase. These
features are imprinted in the radiation emitted by the cavity, which is readily
measurable in state-of-art setups of cavity quantum electrodynamics.Comment: 9 pages, 7 figure
Calcareous nannofossil and foraminifer biostratigraphy of the Campanian–Maastrichtian chalk of the Femern Bælt (Denmark–Germany).
A new study based on calcareous nannofossil and benthic
and planktonic foraminifer biostratigraphy is presented for
the upper Campanian – Maastrichtian chalk of the Femern
Bælt (Denmark and Germany; Fig.1). The results are consistent
with recent studies of the Danish chalk for this interval,
allowing correlation across the Danish Basin and forming the
basis for correlation further afield within the Boreal Realm.
Numerous studies have been carried out recently on the upper
Campanian – Maastrichtian chalk of the Danish Basin,
covering aspects such as sedimentology, depositional environment,
macrofossil biostratigraphy, carbon isotope stratigraphy
as well as nannofossil and dinoflagellate biostratigraphy.
However, very few published studies on foraminifers
exist across this interval in this area. The 09.A.006, 09.A.007
and 09.A.008 boreholes (Fig. 2) were drilled in 2009 in preparation
for construction of a fixed link across the Femern
Bælt, which will connect Denmark to Germany (Rambøll
Arup JV 2011). The boreholes penetrated glacial till, Paleocene–
Eocene clay and chalk (Sheldon et al. 2012). Here, for
the first time, the Boreal foraminifer biostratigraphy of the
late Campanian – Maastrichtian interval is investigated and
presented alongside nannofossil biostratigraphy
Mechanical effects of optical resonators on driven trapped atoms: Ground state cooling in a high finesse cavity
We investigate theoretically the mechanical effects of light on atoms trapped
by an external potential, whose dipole transition couples to the mode of an
optical resonator and is driven by a laser. We derive an analytical expression
for the quantum center-of-mass dynamics, which is valid in presence of a tight
external potential. This equation has broad validity and allows for a
transparent interpretation of the individual scattering processes leading to
cooling. We show that the dynamics are a competition of the mechanical effects
of the cavity and of the laser photons, which may mutually interfere. We focus
onto the good-cavity limit and identify novel cooling schemes, which are based
on quantum interference effects and lead to efficient ground state cooling in
experimentally accessible parameter regimes.Comment: 17 pages, 6 figure
Photon-Mediated Interaction between Two Distant Atoms
We study the photonic interactions between two distant atoms which are
coupled by an optical element (a lens or an optical fiber) focussing part of
their emitted radiation onto each other. Two regimes are distinguished
depending on the ratio between the radiative lifetime of the atomic excited
state and the propagation time of a photon between the two atoms. In the two
regimes, well below saturation the dynamics exhibit either typical features of
a bad resonator, where the atoms act as the mirrors, or typical characteristics
of dipole-dipole interaction. We study the coherence properties of the emitted
light and show that it carries signatures of the multiple scattering processes
between the atoms. The model predictions are compared with the experimental
results in J. Eschner {\it et al.}, Nature {\bf 413}, 495 (2001).Comment: 18 pages, 15 figure
Laser cooling with electromagnetically induced transparency: Application to trapped samples of ions or neutral atoms
A novel method of ground state laser cooling of trapped atoms utilizes the
absorption profile of a three (or multi-) level system which is tailored by a
quantum interference. With cooling rates comparable to conventional sideband
cooling, lower final temperatures may be achieved. The method was
experimentally implemented to cool a single Ca ion to its vibrational
ground state. Since a broad band of vibrational frequencies can be cooled
simultaneously, the technique will be particularly useful for the cooling of
larger ion strings, thereby being of great practical importance for
initializing a quantum register based on trapped ions. We also discuss its
application to different level schemes and for ground state cooling of neutral
atoms trapped by a far detuned standing wave laser field.Comment: 9 pages, 13 figures, submitted to Appl Phys B 200
Correlations and pair emission in the escape dynamics of ions from one-dimensional traps
We explore the non-equilibrium escape dynamics of long-range interacting ions
in one-dimensional traps. The phase space of the few ion setup and its impact
on the escape properties are studied. As a main result we show that an
instantaneous reduction of the trap's potential depth leads to the synchronized
emission of a sequence of ion pairs if the initial configurations are close to
the crystalline ionic configuration. The corresponding time-intervals of the
consecutive pair emission as well as the number of emitted pairs can be tuned
by changing the final trap depth. Correlations between the escape times and
kinetic energies of the ions are observed and analyzed.Comment: 17 pages, 9 figure
Quantum light by atomic arrays in optical resonators
Light scattering by a periodic atomic array is studied when the atoms couple
with the mode of a high-finesse optical resonator and are driven by a laser.
When the von-Laue condition is not satified, there is no coherent emission into
the cavity mode, and the latter is pumped via inelastic scattering processes.
We consider this situation and identify conditions for which different
non-linear optical processes can occur. We show that these processes can be
controlled by suitably tuning the strength of laser and cavity coupling, the
angle between laser and cavity axis, and the array periodicity. We characterize
the coherence properties of the light when the system can either operate as
degenerate parametric amplifier or as a source of antibunched-light. Our study
permits us to identify the individual multi-photon components of the nonlinear
optical response of the atomic array and the corresponding parameter regimes,
thereby in principle allowing one for controlling the nonlinear optical
response of the medium.Comment: 11 pages, 10 figures, version to appear in Phys. Rev.
Inelastic scattering of light by a cold trapped atom: Effects of the quantum center-of-mass motion
The light scattered by a cold trapped ion, which is in the stationary state
of laser cooling, presents features due to the mechanical effects of
atom-photon interaction. These features appear as additional peaks (sidebands)
in the spectrum of resonance fluorescence. Among these sidebands the literature
has discussed the Stokes and anti-Stokes components, namely the sidebands of
the elastic peak. In this manuscript we show that the motion also gives rise to
sidebands of the inelastic peaks. These are not always visible, but, as we
show, can be measured in parameter regimes which are experimentally accessible.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
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