235 research outputs found
A Single Atom as a Mirror of an Optical Cavity
By tightly focussing a laser field onto a single cold ion trapped in front of
a far-distant dielectric mirror, we could observe a quantum electrodynamic
effect whereby the ion behaves as the optical mirror of a Fabry-P\'erot cavity.
We show that the amplitude of the laser field is significantly altered due to a
modification of the electromagnetic mode structure around the atom in a novel
regime in which the laser intensity is already changed by the atom alone. e
propose a direct application of this system as a quantum memory for single
photons.Comment: 7 pages, 3 figures, to appear in Physical Review Letter
QED with a spherical mirror
We investigate the Quantum-Electro-Dynamic properties of an atomic electron
close to the focus of a spherical mirror. We first show that the spontaneous
emission and excited state level shift of the atom can be fully suppressed with
mirror-atom distances of many wavelengths. A three-dimensional theory predicts
that the spectral density of vacuum fluctuations can indeed vanish within a
volume around the atom, with the use of a far distant mirror
covering only half of the atomic emission solid angle. The modification of
these QED atomic properties is also computed as a function of the mirror size
and large effects are found for only moderate numerical apertures. We also
evaluate the long distance ground state energy shift (Casimir-Polder shift) and
find that it scales as at the focus of a hemi-spherical mirror
of radius , as opposed to the well known scaling law for an
atom at a distance from an infinite plane mirror. Our results are relevant
for investigations of QED effects, and also free space coupling to single atoms
using high-numerical aperture lenses.Comment: 12 pages, 4 figure
Electromagnetically Induced Transparency from a Single Atom in Free Space
We report an absorption spectroscopy experiment and the observation of
electromagnetically induced transparency from a single trapped atom. We focus a
weak and narrowband Gaussian light beam onto an optically cooled Barium ion
using a high numerical aperture lens. Extinction of this beam is observed with
measured values of up to 1.3 %. We demonstrate electromagnetically induced
transparency of the ion by tuning a strong control beam over a two-photon
resonance in a three-level lambda-type system. The probe beam extinction is
inhibited by more than 75 % due to population trapping.Comment: 4 pages, 3 figure
Interferometric thermometry of a single sub-Doppler cooled atom
Efficient self-interference of single-photons emitted by a sideband-cooled
Barium ion is demonstrated. First, the technical tools for performing efficient
coupling to the quadrupolar transition of a single Ba ion are
presented. We show efficient Rabi oscillations of the internal state of the ion
using a highly stabilized 1.76 fiber laser resonant with the
S-D transition. We then show sideband cooling of the ion's
motional modes and use it as a means to enhance the interference contrast of
the ion with its mirror-image to up to 90%. Last, we measure the dependence of
the self-interference contrast on the mean phonon number, thereby demonstrating
the potential of the set-up for single-atom thermometry close to the motional
ground state.Comment: 6 pages, 6 figure
Enhanced Spontaneous Emission Into The Mode Of A Cavity QED System
We study the light generated by spontaneous emission into a mode of a cavity
QED system under weak excitation of the orthogonally polarized mode. Operating
in the intermediate regime of cavity QED with comparable coherent and
decoherent coupling constants, we find an enhancement of the emission into the
undriven cavity mode by more than a factor of 18.5 over that expected by the
solid angle subtended by the mode. A model that incorporates three atomic
levels and two polarization modes quantitatively explains the observations.Comment: 9 pages, 2 figures, to appear in May 2007 Optics Letter
Atom-atom entanglement by single-photon detection
A scheme for entangling distant atoms is realized, as proposed in the seminal
paper by Cabrillo et al. [Phys. Rev. A 59, 1025 (1999)]. The protocol is based
on quantum interference and detection of a single photon scattered from two
effectively one meter distant laser-cooled and trapped atomic ions. The
detection of a single photon heralds entanglement of two internal states of the
trapped ions with high rate and with a fidelity limited mostly by atomic
motion. Control of the entangled state phase is demonstrated by changing the
path length of the single-photon interferometer
Beta-decay of nuclei around Se-90. Search for signatures of a N=56 sub-shell closure relevant the r-process
Nuclear structure plays a significant role on the rapid neutron capture
process (r-process) since shapes evolve with the emergence of shells and
sub-shells. There was some indication in neighboring nuclei that we might find
examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90
nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to
determine if this nucleus has in fact a doubly-magic character. The
fragmentation of Xe-136 beam at the National Superconducting Cyclotron
Laboratory at Michigan State University was used to create a cocktail of nuclei
in the A=90 region. We have measured the half lives of twenty-two nuclei near
the r-process path in the A=90 region. The half lives of As-88 and Se-90 have
been measured for the first time. The values were compared with theoretical
predictions in the search for nuclear-deformation signatures of a N=56
sub-shell, and its possible role in the emergence of a potential doubly-magic
Se-90. The impact of such hypothesis on the synthesis of heavy nuclei,
particularly in the production of Sr, Y and Zr elements was investigated with a
weak r-process network. The new half lives agree with results obtained from a
standard global QRPA model used in r-process calculations, indicating that
Se-90 has a quadrupole shape incompatible with a closed N=56 sub-shell in this
region. The impact of the measured Se-90 half-life in comparison with a former
theoretical predication associated with a spherical half-life on the
weak-r-process is shown to be strong
Realization of the quantum Toffoli gate with trapped ions
Algorithms for quantum information processing are usually decomposed into
sequences of quantum gate operations, most often realized with single- and two-
qubit gates[1]. While such operations constitute a universal set for quantum
computation, gates acting on more than two qubits can simplify the
implementation of complex quantum algorithms[2]. Thus, a single three-qubit
operation can replace a complex sequence of two-qubit gates, which in turn
promises faster execution with potentially higher Fidelity. One important
three-qubit operation is the quantum Toffoli gate which performs a NOT
operation on a target qubit depending on the state of two control qubits. Here
we present the first experimental realization of the quantum Toffoli gate in an
ion trap quantum computer. Our implementation is particular effcient as we
directly encode the relevant logic information in the motion of the ion string.
[1] DiVincenzo, D. P. Two-bit gates are universal for quantum computation.
cond-mat/9407022, Phys.Rev. A 51, 1015-1022 (1995). [2] Chiaverini, J. et al.
Realization of quantum error correction. Nature 432, 602-605 (2004).Comment: 11 pages, 2 figure
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