355 research outputs found
Internal-state thermometry by depletion spectroscopy in a cold guided beam of formaldehyde
We present measurements of the internal state distribution of
electrostatically guided formaldehyde. Upon excitation with continuous tunable
ultraviolet laser light the molecules dissociate, leading to a decrease in the
molecular flux. The population of individual guided states is measured by
addressing transitions originating from them. The measured populations of
selected states show good agreement with theoretical calculations for different
temperatures of the molecule source. The purity of the guided beam as deduced
from the entropy of the guided sample using a source temperature of 150K
corresponds to that of a thermal ensemble with a temperature of about 30 K
Cold guided beams of water isotopologs
Electrostatic velocity filtering and guiding is an established technique to
produce high fluxes of cold polar molecules. In this paper we clarify different
aspects of this technique by comparing experiments to detailed calculations. In
the experiment, we produce cold guided beams of the three water isotopologs
H2O, D2O and HDO. Their different rotational constants and orientations of
electric dipole moments lead to remarkably different Stark shift properties,
despite the molecules being very similar in a chemical sense. Therefore, the
signals of the guided water isotopologs differ on an absolute scale and also
exhibit characteristic electrode voltage dependencies. We find excellent
agreement between the relative guided fractions and voltage dependencies of the
investigated isotopologs and predictions made by our theoretical model of
electrostatic velocity filtering.Comment: 14 pages, 13 figures; small changes to the text, updated reference
Trapping of Neutral Rubidium with a Macroscopic Three-Phase Electric Trap
We trap neutral ground-state rubidium atoms in a macroscopic trap based on
purely electric fields. For this, three electrostatic field configurations are
alternated in a periodic manner. The rubidium is precooled in a magneto-optical
trap, transferred into a magnetic trap and then translated into the electric
trap. The electric trap consists of six rod-shaped electrodes in cubic
arrangement, giving ample optical access. Up to 10^5 atoms have been trapped
with an initial temperature of around 20 microkelvin in the three-phase
electric trap. The observations are in good agreement with detailed numerical
simulations.Comment: 4 pages, 4 figure
Electrostatic extraction of cold molecules from a cryogenic reservoir
We present a method which delivers a continuous, high-density beam of slow
and internally cold polar molecules. In our source, warm molecules are first
cooled by collisions with a cryogenic helium buffer gas. Cold molecules are
then extracted by means of an electrostatic quadrupole guide. For ND the
source produces fluxes up to molecules/s with
peak densities up to molecules/cm. For
HCO the population of rovibrational states is monitored by depletion
spectroscopy, resulting in single-state populations up to .Comment: 4 pages, 4 figures, changes to the text, updated figures and
reference
Ab initio molecular dynamics calculations of ion hydration free energies
We apply ab initio molecular dynamics (AIMD) methods in conjunction with the
thermodynamic integration or "lambda-path" technique to compute the intrinsic
hydration free energies of Li+, Cl-, and Ag+ ions. Using the
Perdew-Burke-Ernzerhof functional, adapting methods developed for classical
force field applications, and with consistent assumptions about surface
potential (phi) contributions, we obtain absolute AIMD hydration free energies
(Delta G(hyd)) within a few kcal/mol, or better than 4%, of Tissandier 's [J.
Phys. Chem. A 102, 7787 (1998)] experimental values augmented with the SPC/E
water model phi predictions. The sums of Li+/Cl- and Ag+/Cl- AIMD Delta G(hyd),
which are not affected by surface potentials, are within 2.6% and 1.2 % of
experimental values, respectively. We also report the free energy changes
associated with the transition metal ion redox reaction Ag++Ni+-> Ag+Ni2+ in
water. The predictions for this reaction suggest that existing estimates of
Delta G(hyd) for unstable radiolysis intermediates such as Ni+ may need to be
extensively revised.Comment: 18 pages, 8 figures. This version is essentially the one published in
J. Chem. Phy
Velocity-selected molecular pulses produced by an electric guide
Electrostatic velocity filtering is a technique for the production of
continuous guided beams of slow polar molecules from a thermal gas. We extended
this technique to produce pulses of slow molecules with a narrow velocity
distribution around a tunable velocity. The pulses are generated by
sequentially switching the voltages on adjacent segments of an electric
quadrupole guide synchronously with the molecules propagating at the desired
velocity. This technique is demonstrated for deuterated ammonia (ND),
delivering pulses with a velocity in the range of and a
relative velocity spread of at FWHM. At velocities around
, the pulses contain up to molecules each. The data are
well reproduced by Monte-Carlo simulations, which provide useful insight into
the mechanisms of velocity selection.Comment: 8 pages, 6 figure
Opto-Electrical Cooling of Polar Molecules
We present an opto-electrical cooling scheme for polar molecules based on a
Sisyphus-type cooling cycle in suitably tailored electric trapping fields.
Dissipation is provided by spontaneous vibrational decay in a closed level
scheme found in symmetric-top rotors comprising six low-field-seeking
rovibrational states. A generic trap design is presented. Suitable molecules
are identified with vibrational decay rates on the order of 100Hz. A simulation
of the cooling process shows that the molecular temperature can be reduced from
1K to 1mK in approximately 10s. The molecules remain electrically trapped
during this time, indicating that the ultracold regime can be reached in an
experimentally feasible scheme
Conditional evolution in single-atom cavity QED
We consider a typical setup of cavity QED consisting of a two-level atom
interacting strongly with a single resonant electromagnetic field mode inside a
cavity. The cavity is resonantly driven and the output undergoes continuous
homodyne measurements. We derive an explicit expression for the state of the
system conditional on a discrete photocount record. This expression takes a
particularly simple form if the system is initially in the steady state. As a
byproduct, we derive a general formula for the steady state that had been
conjectured before in the strong driving limit.Comment: 15 pages, 1 postscript figure, added discussion of mode
Deterministic cavity quantum electrodynamics with trapped ions
We have employed radio-frequency trapping to localize a single 40Ca+-ion in a high-finesse optical cavity. By means of laser Doppler cooling, the position spread of the ion's wavefunction along the cavity axis was reduced to 42 nm, a fraction of the resonance wavelength of ionized calcium (λ = 397 nm). By controlling the position of the ion in the optical field, continuous and completely deterministic coupling of ion and field was realized. The precise three-dimensional location of the ion in the cavity was measured by observing the fluorescent light emitted upon excitation in the cavity field. The single-ion system is ideally suited to implement cavity quantum electrodynamics under cw conditions. To this end we operate the cavity on the D3/2–P1/2 transition of 40Ca+ (λ = 866 nm). Applications include the controlled generation of single-photon pulses with high efficiency and two-ion quantum gates
Photon-Photon Entanglement with a Single Trapped Atom
An experiment is performed where a single rubidium atom trapped within a
high-finesse optical cavity emits two independently triggered entangled
photons. The entanglement is mediated by the atom and is characterized both by
a Bell inequality violation of S=2.5, as well as full quantum-state tomography,
resulting in a fidelity exceeding F=90%. The combination of cavity-QED and
trapped atom techniques makes our protocol inherently deterministic - an
essential step for the generation of scalable entanglement between the nodes of
a distributed quantum network.Comment: 5 pages, 4 figure
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