58 research outputs found
Precision spectral manipulation of optical pulses using a coherent photon echo memory
Photon echo schemes are excellent candidates for high efficiency coherent
optical memory. They are capable of high-bandwidth multi-pulse storage, pulse
resequencing and have been shown theoretically to be compatible with quantum
information applications. One particular photon echo scheme is the gradient
echo memory (GEM). In this system, an atomic frequency gradient is induced in
the direction of light propagation leading to a Fourier decomposition of the
optical spectrum along the length of the storage medium. This Fourier encoding
allows precision spectral manipulation of the stored light. In this letter, we
show frequency shifting, spectral compression, spectral splitting, and fine
dispersion control of optical pulses using GEM
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
Coherent population trapping of a single nuclear spin under ambient conditions
Coherent control of quantum systems has far-reaching implications in quantum
engineering. In this context, coherent population trapping (CPT) involving dark
resonances has played a prominent role, leading to a wealth of major
applications including laser cooling of atoms and molecules, optical
magnetometry, light storage and highly precise atomic clocks. Extending CPT
methods to individual solid-state quantum systems has been only achieved in
cryogenic environments for electron spin impurities and superconducting
circuits. Here, we demonstrate efficient CPT of a single nuclear spin in a room
temperature solid. To this end, we make use of a three-level system with a
-configuration in the microwave domain, which consists of nuclear spin
states addressed through their hyperfine coupling to the electron spin of a
single nitrogen-vacancy defect in diamond. Dark state pumping requires a
relaxation mechanism which, in atomic systems, is simply provided by
spontaneous emission. In this work, the relaxation process is externally
controlled through incoherent optical pumping and separated in time from
consecutive coherent microwave excitations of the nuclear spin
-system. Such a pumping scheme with controlled relaxation allows us
(i) to monitor the sequential accumulation of population into the dark state
and (ii) to reach a new regime of CPT dynamics for which periodic arrays of
dark resonances can be observed, owing to multiple constructive interferences.
This work offers new prospects for quantum state preparation, information
storage in hybrid quantum systems and metrology.Comment: 13 pages including supplementary information, links to figures
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Analytic treatment of CRIB Quantum Memories for Light using Two-level Atoms
It has recently been discovered that the optical analogue of a gradient echo
in an optically thick material could form the basis of a optical memory that is
both completely efficient and noise free. Here we present analytical
calculation showing this is the case. There is close analogy between the
operation of the memory and an optical system with two beam splitters. We can
use this analogy to calculate efficiencies as a function of optical depth for a
number of quantum memory schemes based on controlled inhomogeneous broadening.
In particular we show that multiple switching leads to a net 100% retrieval
efficiency for the optical gradient echo even in the optically thin case.Comment: 10 page
An AC Stark Gradient Echo Memory in Cold Atoms
The burgeoning fields of quantum computing and quantum key distribution have
created a demand for a quantum memory. The gradient echo memory scheme is a
quantum memory candidate for light storage that can boast efficiencies
approaching unity, as well as the flexibility to work with either two or three
level atoms. The key to this scheme is the frequency gradient that is placed
across the memory. Currently the three level implementation uses a Zeeman
gradient and warm atoms. In this paper we model a new gradient creation
mechanism - the ac Stark effect - to provide an improvement in the flexibility
of gradient creation and field switching times. We propose this scheme in
concert with a move to cold atoms (~1 mK). These temperatures would increase
the storage times possible, and the small ensemble volumes would enable large
ac Stark shifts with reasonable laser power. We find that memory bandwidths on
the order of MHz can be produced with experimentally achievable laser powers
and trapping volumes, with high precision in gradient creation and switching
times on the order of nanoseconds possible. By looking at the different
decoherence mechanisms present in this system we determine that coherence times
on the order of 10s of milliseconds are possible, as are delay-bandwidth
products of approximately 50 and efficiencies over 90%
Gradient Echo Quantum Memory for Light using Two-level Atoms
We propose a quantum memory for light that is analogous to the NMR gradient
echo. Our proposal is ideally perfectly efficient and provides simplifications
to current 3-level quantum memory schemes based on controlled inhomogeneous
broadening. Our scheme does not require auxiliary light fields. Instead the
input optical pulse interacts only with two-level atoms that have linearly
increasing Stark shifts. By simply reversing the sign of the atomic Stark
shifts, the pulse is retrieved in the forward direction. We present analytical,
numerical and experimental results of this scheme. We report experimental
efficiencies of up to 15% and suggest simple realizable improvements to
significantly increase the efficiency.Comment: 4 pages, 4 figure
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