143 research outputs found
Preparation of spin squeezed atomic states by optical phase shift measurement
In this paper we present a state vector analysis of the generation of atomic
spin squeezing by measurement of an optical phase shift. The frequency
resolution is improved when a spin squeezed sample is used for spectroscopy in
place of an uncorrelated sample. When light is transmitted through an atomic
sample some photons will be scattered out of the incident beam, and this has a
destructive effect on the squeezing. We present quantitative studies for three
limiting cases: the case of a sample of atoms of size smaller than the optical
wavelength, the case of a large dilute sample and the case of a large dense
sample.Comment: 18 page
Unconditional two-mode squeezing of separated atomic ensembles
We propose schemes for the unconditional preparation of a two-mode squeezed
state of effective bosonic modes realized in a pair of atomic ensembles
interacting collectively with optical cavity and laser fields. The scheme uses
Raman transitions between stable atomic ground states and under ideal
conditions produces pure entangled states in the steady state. The scheme works
both for ensembles confined within a single cavity and for ensembles confined
in separate, cascaded cavities.Comment: 4 pages, 2 figure
Light-Matter Quantum Interface
We propose a quantum interface which applies multiple passes of a pulse of
light through an atomic sample with phase/polarization rotations in between the
passes. Our proposal does not require nonclassical light input or measurements
on the system, and it predicts rapidly growing unconditional entanglement of
light and atoms from just coherent inputs. The proposed interface makes it
possible to achieve a number of tasks within quantum information processing
including teleportation between light and atoms, quantum memory for light and
squeezing of atomic and light variables.Comment: 4 pages, 4 figure
Three-dimensional theory for interaction between atomic ensembles and free-space light
Atomic ensembles have shown to be a promising candidate for implementations
of quantum information processing by many recently-discovered schemes. All
these schemes are based on the interaction between optical beams and atomic
ensembles. For description of these interactions, one assumed either a
cavity-QED model or a one-dimensional light propagation model, which is still
inadequate for a full prediction and understanding of most of the current
experimental efforts which are actually taken in the three-dimensional free
space. Here, we propose a perturbative theory to describe the three-dimensional
effects in interaction between atomic ensembles and free-space light with a
level configuration important for several applications. The calculations reveal
some significant effects which are not known before from the other approaches,
such as the inherent mode-mismatching noise and the optimal mode-matching
conditions. The three-dimensional theory confirms the collective enhancement of
the signal-to-noise ratio which is believed to be one of the main advantage of
the ensemble-based quantum information processing schemes, however, it also
shows that this enhancement need to be understood in a more subtle way with an
appropriate mode matching method.Comment: 16 pages, 9 figure
Quantum memory for images - a quantum hologram
Matter-light quantum interface and quantum memory for light are important
ingredients of quantum information protocols, such as quantum networks,
distributed quantum computation, etc. In this Letter we present a spatially
multimode scheme for quantum memory for light, which we call a quantum
hologram. Our approach uses a multi-atom ensemble which has been shown to be
efficient for a single spatial mode quantum memory. Due to the multi-atom
nature of the ensemble it is capable of storing many spatial modes, a feature
critical for the present proposal. A quantum hologram has a higher storage
capacity compared to a classical hologram, and is capable of storing quantum
features of an image, such as multimode superposition and entangled quantum
states, something that a standard hologram is unable to achieve. Due to optical
parallelism, the information capacity of the quantum hologram will obviously
exceed that of a single-mode scheme.Comment: 5 pages, 3 figure
Quantum Description of Nuclear Spin Cooling in a Quantum Dot
We study theoretically the cooling of an ensemble of nuclear spins coupled to
the spin of a localized electron in a quantum dot. We obtain a master equation
for the state of the nuclear spins interacting with a sequence of polarized
electrons that allows us to study quantitatively the cooling process including
the effect of nuclear spin coherences, which can lead to ``dark states'' of the
nuclear system in which further cooling is inhibited. We show that the
inhomogeneous Knight field mitigates this effect strongly and that the
remaining dark state limitations can be overcome by very few shifts of the
electron wave function, allowing for cooling far beyond the dark state limit.
Numerical integration of the master equation indicates, that polarizations
larger than 90% can be achieved within a millisecond timescale.Comment: published version; 9 pages, 4 figure
ОЦЕНКА РИСКА ВЫПОЛНЕНИЯ ЛОГИСТИЧЕСКИХ ПРОЕКТОВ НА НАЧАЛЬНОЙ СТАДИИ
The problem of risk assessment in the logistics projects implementation is studied. The solution for BOL-step in the methodology CL2M is presented. As a result, a theoretical basis for automating the risk assessment of the project in the initial stage, which reduces the likelihood of errors in other stages, is offered.Рассмотрена задача оценки риска при выполнении логистических проектов. Представлено решение для BOL-стадии в рамках методологии CL2M. В результате построена теоретическая основа для автоматизации оценки риска проекта на начальной стадии проектирования, что снижает вероятность ошибок на других стадиях
Measurement schemes for the spin quadratures on an ensemble of atoms
We consider how to measure collective spin states of an atomic ensemble based
on the recent multi-pass approaches for quantum interface between light and
atoms. We find that a scheme with two passages of a light pulse through the
atomic ensemble is efficient to implement the homodyne tomography of the spin
state. Thereby, we propose to utilize optical pulses as a phase-shifter that
rotates the quadrature of the spins. This method substantially simplifies the
geometry of experimental schemes.Comment: 4pages 2 figure
Storage of light in atomic vapor
We report an experiment in which a light pulse is decelerated and trapped in
a vapor of Rb atoms, stored for a controlled period of time, and then released
on demand. We accomplish this storage of light by dynamically reducing the
group velocity of the light pulse to zero, so that the coherent excitation of
the light is reversibly mapped into a collective Zeeman (spin) coherence of the
Rb vapor
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