190 research outputs found
The quantum Rabi model in a superfluid Bose-Einstein condensate
We propose a quantum simulation of the quantum Rabi model in an atomic
quantum dot, which is a single atom in a tight optical trap coupled to the
quasiparticle modes of a superfluid Bose-Einstein condensate. This widely
tunable setup allows to simulate the ultrastrong coupling regime of
light-matter interaction in a system which enjoys an amenable characteristic
timescale, paving the way for an experimental analysis of the transition
between the Jaynes-Cummings and the quantum Rabi dynamics using cold-atom
systems. Our scheme can be naturally extended to simulate multi-qubit quantum
Rabi models. In particular, we discuss the appearance of effective two-qubit
interactions due to phononic exchange, among other features.Comment: Improved version and references adde
Entanglement swapping between spacelike separated atoms
We show a mechanism that projects a pair of neutral two-level atoms from an
initially uncorrelated state to a maximally entangled state while they remain
spacelike separated. The atoms begin both excited in a common electromagnetic
vacuum, and the radiation is collected with a partial Bell-state analyzer. If
the interaction time is short enough and a certain two-photon Bell state is
detected after the interaction, a high degree of entanglement, even maximal,
can be generated while one atom is outside the light cone of the other, for
arbitrary large interatomic distances.Comment: v2: version accepted in Phys. Rev.
Detecting ground state qubit self-excitations in circuit QED: slow quantum anti-Zeno effect
In this work we study an ultrastrong coupled qubit-cavity system subjected to
slow repeated measurements. We demonstrate that even under a few imperfect
measurements it is possible to detect transitions of the qubit from its free
ground state to the excited state. The excitation probability grows
exponentially fast in analogy with the quantum anti-Zeno effect. The dynamics
and physics described in this paper is accessible to current superconducting
circuit technology.Comment: 6 pages, 6 figures. v2: extended published versio
Generation of atom-atom correlations inside and outside the mutual light cone
We analyze whether a pair of neutral two level atoms can become entangled in
a finite time while they remain causally disconnected. The interaction with the
e. m. field is treated perturbatively in the electric dipole approximation. We
start from an initial vacuum state and obtain the final atomic correlations for
the cases where n = 0, 1, or 2 photons are produced in a time t, and also when
the final field state is unknown. Our results show that correlations are
sizable inside and outside the mutual light cone for n= 1 and 2, and also that
quantum correlations become classical by tracing over the field state. For n =
0 we obtain entanglement generation by photon propagation between the atoms,
the correlations come from the indistinguishability of the source for n = 1,
and may give rise to entanglement swapping for n = 2.Comment: v2: Minor changes, references added. v3: full revision, appendix
added. v4: Minor changes. Accepted in Phys. Rev.
The IACOB project: A grid-based automatic tool for the quantitative spectroscopic analysis of O-stars
We present the IACOB grid-based automatic tool for the quantitative
spectroscopic analysis of O-stars. The tool consists of an extensive grid of
FASTWIND models, and a variety of programs implemented in IDL to handle the
observations, perform the automatic analysis, and visualize the results. The
tool provides a fast and objective way to determine the stellar parameters and
the associated uncertainties of large samples of O-type stars within a
reasonable computational time.Comment: 8 pages, 2 figures, 1 table. Proceedings of the "GREAT-ESF Stellar
Atmospheres in the Gaia Era Workshop
Photon exchange and correlations transfer in atom-atom entanglement dynamics
We analyze the entanglement dynamics of a system composed by a pair of
neutral two-level atoms that are initially entangled, and the electromagnetic
field, initially in the vacuum state, within the formalism of perturbative
quantum field theory up to the second order. We show that entanglement sudden
death and revival can occur while the atoms remain spacelike-separated and
therefore cannot be related with photon exchange between the atoms. We
interpret these phenomena as the consequence of a transfer of atom-atom
entanglement to atom-field entanglement and viceversa. We also consider the
different bi-partitions of the system, finding similar relationships between
their entanglement evolutions.Comment: 6 pages, 8 figure
Generating Multimode Entangled Microwaves with a Superconducting Parametric Cavity
In this Letter, we demonstrate the generation of multimode entangled states
of propagating microwaves. The entangled states are generated by parametrically
pumping a multimode superconducting cavity. By combining different pump
frequencies, applied simultaneously to the device, we can produce different
entanglement structures in a programable fashion. The Gaussian output states
are fully characterized by measuring the full covariance matrices of the modes.
The covariance matrices are absolutely calibrated using an in situ microwave
calibration source, a shot noise tunnel junction. Applying a variety of
entanglement measures, we demonstrate both full inseparability and genuine
tripartite entanglement of the states. Our method is easily extensible to more
modes.Comment: 5 pages, 1 figures, 1 tabl
The IACOB project. V. Spectroscopic parameters of the O-type stars in the modern grid of standards for spectral classification
The IACOB and OWN surveys are two ambitious complementary observational
projects which have made available a large multi-epoch spectroscopic database
of optical high resolution spectra of Galactic massive O-type stars. As a first
step in the study of the full sample of (more than 350) O stars surveyed by the
IACOB/OWN projects, we have performed the quantitative spectroscopic analysis
of a subsample of 128 stars included in the modern grid of O-type standards for
spectral classification. We use semi-automatized tools to determine the set of
spectroscopic parameters that can be obtained from the optical spectrum of
O-type stars. We also benefit from the multi-epoch character of the surveys to
perform a spectroscopic variability study of the sample, accounting for
spectroscopic binarity and variability of the main wind diagnostic lines. We
provide a general overview of the stellar and wind parameters of this reference
sample, and updated recipes for the SpT\,--\,Teff/log g calibrations for
Galactic O-type stars. We evaluate our semi-automatized analysis strategy with
40 stars from the literature, and find a good agreement. The agreement
between the synthetic spectra associated with fastwind best fitting models and
the observed spectra is good for most targets, but 46 stars present a
particular behavior of the wind diagnostic lines that cannot be reproduced by
our grid of spherically symmetric unclumped models. These are potential targets
of interest for more detailed investigations of clumpy winds and/or the
existence of additional circumstellar components. Last, our variability study
has led to the detection of signatures of spectroscopic binarity in 27\% of the
stars and small amplitude radial velocity variations in the photospheric lines
of another 30\%. Additionally, 31\% of the investigated stars show variability
in the wind diagnostic lines.Comment: 20 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Dynamics of Atom-Atom Correlations in the Fermi problem
We present a detailed perturbative study of the dynamics of several types of
atom-atom correlations in the famous Fermi problem. This is an archetypal model
to study micro-causality in the quantum domain where two atoms, the first
initially excited and the second prepared in its ground state, interact with
the vacuum electromagnetic field. The excitation can be transferred to the
second atom via a flying photon and various kinds of quantum correlations
between the two are generated during this process. Among these, prominent
examples are given by entanglement, quantum discord and nonlocal correlations.
It is the aim of this paper to analyze the role of the light cone in the
emergence of such correlations.Comment: 14 pages, 7 figure
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