186 research outputs found
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
Double-EIT ground-state laser cooling without blue-sideband heating
We discuss a laser cooling scheme for trapped atoms or ions which is based on
double electromagnetically induced transparency (EIT) and makes use of a
four-level atom in tripod configuration. The additional fourth atomic state is
coupled by a strong coupling laser field to the usual three-level setup of
single-EIT cooling. This effectively allows to create two EIT structures in the
absorption spectrum of the system to be cooled, which may be controlled by the
coupling laser field parameters to cancel both the carrier- and the
blue-sideband excitations. In leading order of the Lamb-Dicke expansion, this
suppresses all heating processes. As a consequence, the double-EIT scheme can
be used to lower the cooling limit by almost two powers of the Lamb-Dicke
parameter as compared to single-EIT cooling.Comment: 7 pages, 3 figure
Motional frequency shifts of trapped ions in the Lamb-Dicke regime
First order Doppler effects are usually ignored in laser driven trapped ions
when the recoil frequency is much smaller than the trapping frequency
(Lamb-Dicke regime). This means that the central, carrier excitation band is
supposed to be unaffected by vibronic transitions in which the vibrational
number changes. While this is strictly true in the Lamb-Dicke limit (infinitely
tight confinement), the vibronic transitions do play a role in the Lamb-Dicke
regime. In this paper we quantify the asymptotic behaviour of their effect with
respect to the Lamb-Dicke parameter. In particular, we give analytical
expressions for the frequency shift, ``pulling'' or ``pushing'', produced in
the carrier absorption band by the vibronic transitions both for Rabi and
Ramsey schemes. This shift is shown to be independent of the initial
vibrational state.Comment: 9 pages, 6 figure
Dissipative quantum control of a spin chain
A protocol is discussed for preparing a spin chain in a generic many-body
state in the asymptotic limit of tailored non-unitary dynamics. The dynamics
require the spectral resolution of the target state, optimized coherent pulses,
engineered dissipation, and feedback. As an example, we discuss the preparation
of an entangled antiferromagnetic state, and argue that the procedure can be
applied to chains of trapped ions or Rydberg atoms.Comment: 5 pages, 4 figure
Optical decay from a Fabry-Perot cavity faster than the decay time
The dynamical response of an optical Fabry-Perot cavity is investigated
experimentally. We observe oscillations in the transmitted and reflected light
intensity if the frequency of the incoupled light field is rapidly changed. In
addition, the decay of a cavity-stored light field is accelerated if the phase
and intensity of the incoupled light are switched in an appropriate way. The
theoretical model by M. J. Lawrence em et al, JOSA B 16, 523 (1999) agrees with
our observations.Comment: submitted to Josa
Coherent generation of EPR-entangled light pulses mediated by a single trapped atom
We show that a single, trapped, laser-driven atom in a high-finesse optical
cavity allows for the quantum-coherent generation of entangled light pulses on
demand. Schemes for generating simultaneous and temporally separated pulse
pairs are proposed. The mechanical effect of the laser excitation on the
quantum motion of the cold trapped atom mediates the entangling interaction
between two cavity modes and between the two subsequent pulses, respectively.
The entanglement is of EPR-type, and its degree can be controlled through
external parameters. At the end of the generation process the atom is
decorrelated from the light field. Possible experimental implementations of the
proposals are discussed.Comment: 11 pages, 4 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
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