216 research outputs found
Core-valence correlations for atoms with open shells
We present an efficient method of inclusion of the core-valence correlations
into the configuration interaction (CI) calculations. These correlations take
place in the core area where the potential of external electrons is
approximately constant. A constant potential does not change the core electron
wave functions and Green's functions. Therefore, all operators describing
interaction of valence electrons and core electrons (the core part of
the Hartree-Fock Hamiltonian
, the correlation potential and
the screening of interaction between valence electrons by the core electrons
) may be calculated with all
valence electrons removed. This allows one to avoid subtraction diagrams
which make accurate inclusion of the core-valence correlations for
prohibitively complicated. Then the CI Hamiltonian for valence electrons is
calculated using orbitals in complete potential (the mean field
produced by all electrons); + are added to the CI
Hamiltonian to account for the core-valence correlations. We calculate
and using many-body perturbation theory in which
dominating classes of diagrams are included in all orders.
We use neutral Xe I and all positive ions up to Xe VIII as a testing ground.
We found that the core electron density for all these systems is practically
the same. Therefore, we use the same and to build
the CI Hamiltonian in all these systems (). Good agreement
with experiment for energy levels and Land\'{e} factors is demonstrated for all
cases from Xe I to Xe VIII.Comment: 13 pages, 5 figure
Colloquium: Physics of optical lattice clocks
Recently invented and demonstrated, optical lattice clocks hold great promise
for improving the precision of modern timekeeping. These clocks aim at the
10^-18 fractional accuracy, which translates into a clock that would neither
lose or gain a fraction of a second over an estimated age of the Universe. In
these clocks, millions of atoms are trapped and interrogated simultaneously,
dramatically improving clock stability. Here we discuss the principles of
operation of these clocks and, in particular, a novel concept of "magic"
trapping of atoms in optical lattices. We also highlight recently proposed
microwave lattice clocks and several applications that employ the optical
lattice clocks as a platform for precision measurements and quantum information
processing.Comment: 18 pages, 15 figure
Two-photon E1M1 decay of 2 3P0 states in heavy heliumlike ions
Two-photon E1M1 transition rates are evaluated for heliumlike ions with
nuclear charges in the range Z = 50-94. The two-photon rates modify previously
published lifetimes/transition rates of 2 3P0 states. For isotopes with nuclear
spin I not equal 0, where hyperfine quenching dominates the 2 3P0 decay,
two-photon contributions are significant; for example, in heliumlike 187 Os the
two-photon correction is 3% of the total rate. For isotopes with I= 0, where
the 2 3P0 decay is unquenched, the E1M1 corrections are even more important
reaching 60% for Z=94. Therefore, to aid in the interpretation of experiments
on hyperfine quenching in heliumlike ions and to provide a more complete
database for unquenched transitions, a knowledge of E1M1 rates is important.Comment: 6 pages, 3 figures, 3 table
Quantum network of neutral atom clocks
We propose a protocol for creating a fully entangled GHZ-type state of
neutral atoms in spatially separated optical atomic clocks. In our scheme,
local operations make use of the strong dipole-dipole interaction between
Rydberg excitations, which give rise to fast and reliable quantum operations
involving all atoms in the ensemble. The necessary entanglement between distant
ensembles is mediated by single-photon quantum channels and collectively
enhanced light-matter couplings. These techniques can be used to create the
recently proposed quantum clock network based on neutral atom optical clocks.
We specifically analyze a possible realization of this scheme using neutral Yb
ensembles.Comment: 13 pages, 11 figure
AC Stark shift of the Cs microwave atomic clock transitions
We analyze the AC Stark shift of the Cs microwave atomic clock transition
theoretically and experimentally. Theoretical and experimental data are in a
good agreement with each other. Results indicate the absence of a magic
wavelength at which there would be no differential shift of the clock states
having zero projections of the total angular momentum
On the feasibility of cooling and trapping metastable alkaline-earth atoms
Metastability and long-range interactions of Mg, Ca, and Sr in the
lowest-energy metastable state are investigated. The calculated
lifetimes are 38 minutes for Mg*, 118 minutes for Ca*, and 17 minutes for Sr*,
supporting feasibility of cooling and trapping experiments. The
quadrupole-quadrupole long-range interactions of two metastable atoms are
evaluated for various molecular symmetries. Hund's case (c) 4_g potential
possesses a large 100-1000 K potential barrier. Therefore magnetic trap losses
can possibly be reduced using cold metastable atoms in a stretched M=2 state.
Calculations were performed in the framework of ab initio relativistic
configuration interaction method coupled with the random-phase approximation.Comment: 8 pages, 2 figures; to appear in PR
Ultracold collision properties of metastable alkaline-earth atoms
Ultra-cold collisions of spin-polarized 24Mg,40Ca, and 88Sr in the metastable
3P2 excited state are investigated. We calculate the long-range interaction
potentials and estimate the scattering length and the collisional loss rate as
a function of magnetic field. The estimates are based on molecular potentials
between 3P2 alkaline-earth atoms obtained from ab initio atomic and molecular
structure calculations. The scattering lengths show resonance behavior due to
the appearance of a molecular bound state in a purely long-range interaction
potential and are positive for magnetic fields below 50 mT. A loss-rate model
shows that losses should be smallest near zero magnetic field and for fields
slightly larger than the resonance field, where the scattering length is also
positive.Comment: 4 pages, 4 figure
High-accuracy relativistic many-body calculations of van der Waals coefficients C_6 for alkaline-earth atoms
Relativistic many-body calculations of van der Waals coefficients C_6 for
dimers correlating to two ground state alkaline-earth atoms at large
internuclear separations are reported. The following values and uncertainties
were determined : C_6 = 214(3) for Be, 627(12) for Mg, 2221(15) for Ca,
3170(196) for Sr, and 5160(74) for Ba in atomic units.Comment: 5 pages, submitted to Phys. Rev.
Correlated many-body treatment of Breit interaction with application to cesium atomic properties and parity violation
Corrections from Breit interaction to basic properties of atomic 133Cs are
determined in the framework of third-order relativistic many-body perturbation
theory. The corrections to energies, hyperfine-structure constants,
off-diagonal hyperfine 6S-7S amplitude, and electric-dipole matrix elements are
tabulated. It is demonstrated that the Breit corrections to correlations are
comparable to the Breit corrections at the Dirac-Hartree-Fock level.
Modification of the parity-nonconserving (PNC) 6S-7S amplitude due to Breit
interaction is also evaluated; the resulting weak charge of Cs shows no
significant deviation from the prediction of the standard model of elementary
particles. The neutron skin correction to the PNC amplitude is also estimated
to be -0.2% with an error bound of 30% based on the analysis of recent
experiments with antiprotonic atoms. The present work supplements publication
[A. Derevianko, Phys. Rev. Lett. 85, 1618 (2000)] with a discussion of the
formalism and provides additional numerical results and updated discussion of
parity violation.Comment: 16 pages; 5 figs; submitted to Phys. Rev.
Doppler cooling of three-level -systems by coherent pulse trains
We explore the possibility of decelerating and Doppler cooling an ensemble of
tree-level -type atoms by a coherent train of short, non-overlapping
laser pulses. We show that -atoms can be Doppler cooled without
additional repumping of the population from the intermediate ground state. We
derive analytical expression for the scattering force in the quasi-steady-state
regime and analyze its dependence on pulse train parameters. Based on this
analysis we propose a method of choosing pulse train parameters to optimize the
cooling process.Comment: 22 pages, 6 figure
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