106,492 research outputs found
Measurement of dynamic Stark polarizabilities by analyzing spectral lineshapes of forbidden transitions
We present a measurement of the dynamic scalar and tensor polarizabilities of
the excited state 3D1 in atomic ytterbium. The polarizabilities were measured
by analyzing the spectral lineshape of the 408-nm 1S0->3D1 transition driven by
a standing wave of resonant light in the presence of static electric and
magnetic fields. Due to the interaction of atoms with the standing wave, the
lineshape has a characteristic polarizability-dependent distortion. A
theoretical model was used to simulate the lineshape and determine a
combination of the polarizabilities of the ground and excited states by fitting
the model to experimental data. This combination was measured with a 13%
uncertainty, only 3% of which is due to uncertainty in the simulation and
fitting procedure. The scalar and tensor polarizabilities of the state 3D1 were
measured for the first time by comparing two different combinations of
polarizabilities. We show that this technique can be applied to similar atomic
systems.Comment: 13 pages, 7 figures, submitted to PR
1/N_c corrections to the magnetic susceptibility of the QCD vacuum
We investigate the magnetic susceptibility of the QCD vacuum with the
corrections taken into account, based on the instanton vacuum. Starting from
the instanton liquid model we derive the gauged light-quark partition function
in the presence of the current quark mass as well as of external Abelian vector
and tensor fields. We consider the meson-loop corrections which are
shown to contribute to the magnetic susceptibility by around 15% for the up
(and down) quarks. We also take into account the tensor terms of the
quark-quark interaction from the instanton vacuum as well as the finite-width
effects, both of which are of order . The effects of the
tensor terms and finite width turn out to be negligibly small. The final
results for the up-quarks are given as: with the quark condensate . We also
discuss the pion mass dependence of the magnetic susceptibility in order to
give a qualitative guideline for the chiral extrapolation of lattice data.Comment: 18 pages, 5 figures. Final version to appear in Phys. Rev.
Trapped atoms in spatially-structured vector light fields
Spatially-structured laser beams, eventually carrying orbital angular
momentum, affect electronic transitions of atoms and their motional states in a
complex way. We present a general framework, based on the spherical tensor
decomposition of the interaction Hamiltonian, for computing atomic transition
matrix elements for light fields of arbitrary spatial mode and polarization
structures. We study both the bare electronic matrix elements, corresponding to
transitions with no coupling to the atomic center-of-mass motion, as well as
the matrix elements describing the coupling to the quantized atomic motion in
the resolved side-band regime. We calculate the spatial dependence of
electronic and motional matrix elements for tightly focused Hermite-Gaussian,
Laguerre-Gaussian and for radially and azimuthally polarized beams. We show
that near the diffraction limit, all these beams exhibit longitudinal fields
and field gradients, which strongly affect the selection rules and could be
used to tailor the light-matter interaction. The presented framework is useful
for describing trapped atoms or ions in spatially-structured light fields and
therefore for designing new protocols and setups in quantum optics, -sensing
and -information processing
Quantum control and measurement of atomic spins in polarization spectroscopy
Quantum control and measurement are two sides of the same coin. To affect a
dynamical map, well-designed time-dependent control fields must be applied to
the system of interest. To read out the quantum state, information about the
system must be transferred to a probe field. We study a particular example of
this dual action in the context of quantum control and measurement of atomic
spins through the light-shift interaction with an off-resonant optical probe.
By introducing an irreducible tensor decomposition, we identify the coupling of
the Stokes vector of the light field with moments of the atomic spin state.
This shows how polarization spectroscopy can be used for continuous weak
measurement of atomic observables that evolve as a function of time.
Simultaneously, the state-dependent light shift induced by the probe field can
drive nonlinear dynamics of the spin, and can be used to generate arbitrary
unitary transformations on the atoms. We revisit the derivation of the master
equation in order to give a unified description of spin dynamics in the
presence of both nonlinear dynamics and photon scattering. Based on this
formalism, we review applications to quantum control, including the design of
state-to-state mappings, and quantum-state reconstruction via continuous weak
measurement on a dynamically controlled ensemble
Calibration of Spin-Light Coupling by Coherently Induced Faraday Rotation
Calibrating the strength of the light-matter interaction is an important
experimental task in quantum information and quantum state engineering
protocols. The strength of the off-resonant light-matter interaction in
multi-atom spin oscillators can be characterized by the coupling rate
. Here we utilize the Coherently Induced Faraday Rotation
(CIFAR) signal for determining the coupling rate. The method is suited for both
continuous and pulsed readout of the spin oscillator, relying only on applying
a known polarization modulation to the probe laser beam and detecting a known
optical polarization component. Importantly, the method does not require
changes to the optical and magnetic fields performing the state preparation and
probing. The CIFAR signal is also independent of the probe beam photo-detection
quantum efficiency, and allows direct extraction of other parameters of the
interaction, such as the tensor coupling , and the damping rate
. We verify this method in the continuous wave regime, probing
a strongly coupled spin oscillator prepared in a warm cesium atomic vapour.Comment: 15 pages, 6 figure
Space-Time Intervals Underlie Human Conscious Experience, Gravity, and a Theory of Everything
Space-time intervals are the fundamental components of conscious experience, gravity, and a Theory of Everything. Space-time intervals are relationships that arise naturally between events. They have a general covariance (independence of coordinate systems, scale invariance), a physical constancy, that encompasses all frames of reference. There are three basic types of space-time intervals (light-like, time-like, space-like) which interact to create space-time and its properties. Human conscious experience is a four-dimensional space-time continuum created through the processing of space-time intervals by the brain; space-time intervals are the source of conscious experience (observed physical reality). Human conscious experience is modeled by Einstein’s special theory of relativity, a theory designed specifically from the general covariance of space-time intervals (for inertial frames of reference). General relativity is our most accurate description of gravity. In general relativity, the general covariance of space-time intervals is extended to all frames of reference (inertial and non-inertial), including gravitational reference frames; space-time intervals are the source of gravity in general relativity. The general covariance of space-time intervals is further extended to quantum mechanics; space-time intervals are the source of quantum gravity. The general covariance of space-time intervals seamlessly merges general relativity with quantum field theory (the two grand theories of the universe). Space-time intervals consequently are the basis of a Theory of Everything (a single all-encompassing coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe). This theoretical framework encompasses our observed physical reality (conscious experience) as well; space-time intervals link observed physical reality to actual physical reality. This provides an accurate and reliable match between observed physical reality and the physical universe by which we can carry on our activity. The Minkowski metric, which defines generally covariant space-time intervals, may be considered an axiom (premise, postulate) for the Theory of Everything
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