666 research outputs found
Photon-added coherent states as nonlinear coherent states
The states , defined as up to a
normalization constant and is a nonnegative integer, are shown to be the
eigenstates of where is a nonlinear
function of the number operator . The explicit form of
is constructed. The eigenstates of this operator for negative values of are
introduced. The properties of these states are discussed and compared with
those of the state .Comment: Rev Tex file with two figures as postscript files attached. Email:
[email protected]
Multi-mode mediated exchange coupling in cavity QED
Microwave cavities with high quality factors enable coherent coupling of
distant quantum systems. Virtual photons lead to a transverse exchange
interaction between qubits, when they are non-resonant with the cavity but
resonant with each other. We experimentally probe the inverse scaling of the
inter-qubit coupling with the detuning from a cavity mode and its
proportionality to the qubit-cavity interaction strength. We demonstrate that
the enhanced coupling at higher frequencies is mediated by multiple
higher-harmonic cavity modes. Moreover, in the case of resonant qubits, the
symmetry properties of the system lead to an allowed two-photon transition to
the doubly excited qubit state and the formation of a dark state.Comment: 9 pages, 6 figure
Real-time analysis of gene regulation by glucocorticoid hormones
There is increasing evidence that temporal factors are important in allowing
cells to gain additional information from external factors, such as hormones and
cytokines. We sought to discover how cell responses to glucocorticoids develop
over time, and how the response kinetics vary according to ligand structure and
concentration, and hence have developed a continuous gene transcription
measurement system, based on an interleukin-6 (IL-6) luciferase reporter gene.
We measured the time to maximal response, maximal response and integrated
response, and have compared these results with a conventional, end point
glucocorticoid bioassay. We studied natural glucocorticoids (corticosterone and
cortisol), synthetic glucocorticoids (dexamethasone) and glucocorticoid
precursors with weak, or absent bioactivity. We found a close correlation
between half maximal effective concentration (EC50) for maximal response, and
for integrated response, but with consistently higher EC50 for the latter. There
was no relation between the concentration of ligand and the time to maximal
response. A comparison between conventional end point assays and real-time
measurement showed similar effects for dexamethasone and hydrocortisone, with a
less effective inhibition of IL-6 seen with corticosterone. We profiled the
activity of precursor steroids, and found pregnenolone, progesterone,
21-hydroxyprogesterone and 17-hydroxyprogesterone all to be ineffective in the
real-time assay, but in contrast, progesterone and 21-hydroxyprogesterone showed
an IL-6 inhibitory activity in the end point assay. Taken together, our data
show how ligand concentration can alter the amplitude of glucocorticoid
response, and also that a comparison between real-time and end point assays
reveals an unexpected diversity of the function of glucocorticoid precursor
steroids, with implications for human disorders associated with their
overproduction
Reconstructing the density operator by using generalized field quadratures
The Wigner function for one and two-mode quantum systems is explicitely
expressed in terms of the marginal distribution for the generic linearly
transformed quadratures. Then, also the density operator of those systems is
written in terms of the marginal distribution of these quadratures. Some
examples to apply this formalism, and a reduction to the usual optical homodyne
tomography are considered.Comment: 17 pages, Latex,accepted by Quantum and Semiclassical Optic
Characterizing heralded single-photon sources with imperfect measurement devices
Any characterization of a single-photon source is not complete without
specifying its second-order degree of coherence, i.e., its function.
An accurate measurement of such coherence functions commonly requires
high-precision single-photon detectors, in whose absence, only time-averaged
measurements are possible. It is not clear, however, how the resulting
time-averaged quantities can be used to properly characterize the source. In
this paper, we investigate this issue for a heralded source of single photons
that relies on continuous-wave parametric down-conversion. By accounting for
major shortcomings of the source and the detectors--i.e., the multiple-photon
emissions of the source, the time resolution of photodetectors, and our chosen
width of coincidence window--our theory enables us to infer the true source
properties from imperfect measurements. Our theoretical results are
corroborated by an experimental demonstration using a PPKTP crystal pumped by a
blue laser, that results in a single-photon generation rate about 1.2 millions
per second per milliwatt of pump power. This work takes an important step
toward the standardization of such heralded single-photon sources.Comment: 18 pages, 9 figures; corrected Eq. (11) and the description follows
Eq. (22
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
Extended Gaussian wave packet dynamics
We examine an extension to the theory of Gaussian wave packet dynamics in a
one-dimensional potential by means of a sequence of time dependent displacement
and squeezing transformations. Exact expressions for the quantum dynamics are
found, and relationships are explored between the squeezed system, Gaussian
wave packet dynamics, the time dependent harmonic oscillator, and wave packet
dynamics in a Gauss-Hermite basis. Expressions are given for the matrix
elements of the potential in some simple cases. Several examples are given,
including the propagation of a non-Gaussian initial state in a Morse potential
Entangled States and Entropy Remnants of a Photon-Electron System
In the present paper an example of entanglement between two different kinds
of interacting particles, photons and electrons is analysed. The initial-value
problem of the Schroedinger equation is solved non-perturbatively for the
system of a free electron interacting with a quantized mode of the
electromagnetic radiation. Wave packets of the dressed states so obtained are
constructed in order to describe the spatio-temporal separation of the
subsystems before and after the interaction. The joint probability amplitudes
are calculated for the detection of the electron at some space-time location
and the detection of a definite number of photons. The analytical study of the
time evolution of entanglement between the initially separated electron wave
packet and the radiation mode leads to the conclusion that in general there are
non-vanishing entropy remnants in the subsystems after the interaction. On the
basis of the simple model to be presented here, the calculated values of the
entropy remnants crucially depend on the character of the switching-on and off
of the interaction.Comment: 12 pages, 2 figure
Hanbury Brown-Twiss interferometry and second-order correlations of inflaton quanta
The quantum theory of optical coherence is applied to the scrutiny of the
statistical properties of the relic inflaton quanta. After adapting the
description of the quantized scalar and tensor modes of the geometry to the
analysis of intensity correlations, the normalized degrees of first-order and
second-order coherence are computed in the concordance paradigm and are shown
to encode faithfully the statistical properties of the initial quantum state.
The strongly bunched curvature phonons are not only super-Poissonian but also
super-chaotic. Testable inequalities are derived in the limit of large angular
scales and can be physically interpreted in the light of the tenets of Hanbury
Brown-Twiss interferometry. The quantum mechanical results are compared and
contrasted with different situations including the one where intensity
correlations are the result of a classical stochastic process. The survival of
second-order correlations (not necessarily related to the purity of the initial
quantum state) is addressed by defining a generalized ensemble where
super-Poissonian statistics is an intrinsic property of the density matrix and
turns out to be associated with finite volume effects which are expected to
vanish in the thermodynamic limit.Comment: 42 pages, 3 included figures; corrected typos; to appear in Physical
Review
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