249 research outputs found
Normal-mode spectroscopy of a single bound atom-cavity system
The energy-level structure of a single atom strongly coupled to the mode of a
high-finesse optical cavity is investigated. The atom is stored in an
intracavity dipole trap and cavity cooling is used to compensate for inevitable
heating. Two well-resolved normal modes are observed both in the cavity
transmission and the trap lifetime. The experiment is in good agreement with a
Monte Carlo simulation, demonstrating our ability to localize the atom to
within at a cavity antinode.Comment: 4 pages, 4 figure
Trapping and observing single atoms in the dark
A single atom strongly coupled to a cavity mode is stored by
three-dimensional confinement in blue-detuned cavity modes of different
longitudinal and transverse order. The vanishing light intensity at the trap
center reduces the light shift of all atomic energy levels. This is exploited
to detect a single atom by means of a dispersive measurement with 95%
confidence in 0.010 ms, limited by the photon-detection efficiency. As the atom
switches resonant cavity transmission into cavity reflection, the atom can be
detected while scattering about one photon
Momentum diffusion for coupled atom-cavity oscillators
It is shown that the momentum diffusion of free-space laser cooling has a
natural correspondence in optical cavities when the internal state of the atom
is treated as a harmonic oscillator. We derive a general expression for the
momentum diffusion which is valid for most configurations of interest: The atom
or the cavity or both can be probed by lasers, with or without the presence of
traps inducing local atomic frequency shifts. It is shown that, albeit the
(possibly strong) coupling between atom and cavity, it is sufficient for
deriving the momentum diffusion to consider that the atom couples to a mean
cavity field, which gives a first contribution, and that the cavity mode
couples to a mean atomic dipole, giving a second contribution. Both
contributions have an intuitive form and present a clear symmetry. The total
diffusion is the sum of these two contributions plus the diffusion originating
from the fluctuations of the forces due to the coupling to the vacuum modes
other than the cavity mode (the so called spontaneous emission term). Examples
are given that help to evaluate the heating rates induced by an optical cavity
for experiments operating at low atomic saturation. We also point out
intriguing situations where the atom is heated although it cannot scatter
light.Comment: More information adde
Single-atom trajectories in higher-order transverse modes of a high-finesse optical cavity
Transits of single atoms through higher-order Hermite-Gaussian transverse
modes of a high-finesse optical cavity are observed. Compared to the
fundamental Gaussian mode, the use of higher-order modes increases the
information on the atomic position. The experiment is a first experimental step
towards the realisation of an atomic kaleidoscope.Comment: 6 pages, d figure
Network-based dissolution
We introduce a novel graph-theoretic dissolution model which applies to a number of redistribution scenarios such as gerrymandering or work economization. The central aspect of our model is to delete some vertices and redistribute their "load" to neighboring vertices in a completely balanced way. We investigate how the underlying graph structure, the pre-knowledge about which vertices to delete, and the relation between old and new "vertex load" influence the computational complexity of the underlying easy-to-describe graph problems, thereby identifying both tractable and intractable cases
Light force fluctuations in a strongly coupled atom-cavity system
Between mirrors, the density of electromagnetic modes differs from the one in free space. This changes the radiation properties of an atom as well as the light forces acting on an atom. It has profound consequences in the strong-coupling regime of cavity quantum electrodynamics. For a single atom trapped inside the cavity, we investigate the atom-cavity system by scanning the frequency of a probe laser for various atom-cavity detunings. The avoided crossing between atom and cavity resonance is visible in the transmission of the cavity. It is also visible in the loss rate of the atom from the intracavity dipole trap. On the normal-mode resonances, the dominant contribution to the loss rate originates from dipole-force fluctuations which are dramatically enhanced in the cavity. This conclusion is supported by Monte-Carlo simulations
Cavity cooling of a single atom
All conventional methods to laser-cool atoms rely on repeated cycles of
optical pumping and spontaneous emission of a photon by the atom. Spontaneous
emission in a random direction is the dissipative mechanism required to remove
entropy from the atom. However, alternative cooling methods have been proposed
for a single atom strongly coupled to a high-finesse cavity; the role of
spontaneous emission is replaced by the escape of a photon from the cavity.
Application of such cooling schemes would improve the performance of atom
cavity systems for quantum information processing. Furthermore, as cavity
cooling does not rely on spontaneous emission, it can be applied to systems
that cannot be laser-cooled by conventional methods; these include molecules
(which do not have a closed transition) and collective excitations of Bose
condensates, which are destroyed by randomly directed recoil kicks. Here we
demonstrate cavity cooling of single rubidium atoms stored in an intracavity
dipole trap. The cooling mechanism results in extended storage times and
improved localization of atoms. We estimate that the observed cooling rate is
at least five times larger than that produced by free-space cooling methods,
for comparable excitation of the atom
Nuclear matrix element for two neutrino double beta decay from 136Xe
The nuclear matrix element for the two neutrino double beta decay (DBD) of
136Xe was evaluated by FSQP (Fermi Surface Quasi Particle model), where
experimental GT strengths measured by the charge exchange reaction and those by
the beta decay rates were used. The 2 neutrino DBD matrix element is given by
the sum of products of the single beta matrix elements via low-lying (Fermi
Surface) quasi-particle states in the intermediate nucleus. 136Xe is the
semi-magic nucleus with the closed neutron-shell, and the beta + transitions
are almost blocked. Thus the 2 neutrino DBD is much suppressed. The evaluated 2
neutrino DBD matrix element is consistent with the observed value.Comment: 7 pages 6 figure
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