447 research outputs found
"Dressing" lines and vertices in calculations of matrix elements with the coupled-cluster method and determination of Cs atomic properties
We consider evaluation of matrix elements with the coupled-cluster method.
Such calculations formally involve infinite number of terms and we devise a
method of partial summation (dressing) of the resulting series. Our formalism
is built upon an expansion of the product of cluster amplitudes
into a sum of -body insertions. We consider two types of insertions:
particle/hole line insertion and two-particle/two-hole
random-phase-approximation-like insertion. We demonstrate how to ``dress''
these insertions and formulate iterative equations. We illustrate the dressing
equations in the case when the cluster operator is truncated at single and
double excitations. Using univalent systems as an example, we upgrade
coupled-cluster diagrams for matrix elements with the dressed insertions and
highlight a relation to pertinent fourth-order diagrams. We illustrate our
formalism with relativistic calculations of hyperfine constant and
electric-dipole transition amplitude for Cs atom. Finally,
we augment the truncated coupled-cluster calculations with otherwise omitted
fourth-order diagrams. The resulting analysis for Cs is complete through the
fourth-order of many-body perturbation theory and reveals an important role of
triple and disconnected quadruple excitations.Comment: 16 pages, 7 figures; submitted to Phys. Rev.
Precision measurement noise asymmetry and its annual modulation as a dark matter signature
Dark matter may be composed of ultralight quantum fields that form
macroscopic objects. As the Earth moves through the galaxy, interactions with
such objects may leave transient signatures in terrestrial experiments. These
signatures may be sought by analyzing correlations between multiple devices in
a distributed network. However, if the objects are small (<~10^3 km) it becomes
unlikely that more than one device will be affected in a given event. Such
models may, however, induce an observable asymmetry in the noise distributions
of precision measurement devices, such as atomic clocks. Further, an annual
modulation in this asymmetry is expected. Such an analysis may be performed
very simply using existing data, and would be sensitive to models with a high
event rate, even if individual events cannot be resolved. For certain models,
our technique extends the discovery reach beyond that of existing experiments
by many orders of magnitude
Ion clock and search for the variation of the fine structure constant using optical transitions in Nd and Sm
We study ultranarrow - transitions in Nd and
Sm and demonstrate that they lie in the optical region. The transitions
are insensitive to external perturbations. At the same time they are sensitive
to the variation of the fine structure constant . The fractional
accuracy of the frequency of the transitions can be smaller than ,
which may provide a basis for atomic clocks of superb accuracy. Sensitivity to
the variation of approaches per year.Comment: 4 pages, 2 tables, no figure
Magic frequencies for cesium primary frequency standard
We consider microwave hyperfine transitions in the ground state of cesium and
rubidium atoms which are presently used as the primary and the secondary
frequency standards. The atoms are confined in an optical lattice generated by
a circularly polarized laser field. We demonstrate that applying an external
magnetic field with appropriately chosen direction may cancel dynamic Stark
frequency shift making the frequency of the clock transition insensitive to the
strengths of both the laser and the magnetic fields. This can be attained for
practically any laser frequency which is sufficiently distant from a resonance.Comment: 4 pages, 2 figure
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