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Sensor Electronics and Microsystem Technologies

QUANTUM MEASURE OF FREQUENCY AND SENSING THE COLLISIONAL SHIFT OF THE YTTERBIUM HYPERFINE LINES IN MEDIUM OF HELIUM GAS

Andrey V. Loboda, E. V. Mischenko, Yu. V. Dubrovskaya, А. А. Свинаренко

Published Feb 10, 2009• 6 citations
Publisher

Abstract

A problems of constructing the ytterbium quantum measure of frequency and sensing the collisional shift of the ytterbium hyperfine structure (HFS) lines in a medium of bath (He) gas are studied. Relativistic approach is used in calculating the inter atomic potentials, oscillator strengths, HFS collision shift and broadening for ytterbium atom in a medium of helium bath gas.

DOI
10.18524/1815-7459.2009.1.115293

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A problems of constructing the ytterbium quantum measure of frequency and sensing the collisional shift of the ytterbium hyperfine structure (HFS) lines in a medium of bath (He) gas are studied. Relativistic approach is used in calculating the inter atomic potentials, oscillator strengths, HFS collision shift and broadening for ytterbium atom in a medium of helium bath gas.
Transitions between hyperfine structure states of antiprotonic 4He^4 \mathrm{He}4He at collisions with medium atoms: interaction \emph{ab initio}
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We report an experimental and theoretical study on the shift of the hyperfine splitting frequency of ground-state Li atoms in noble gases, He, Ne, Ar, and Xe. The frequency shift is due to the change in the electron-spin density at the Li nuclei induced by collisions to the noble-gas atoms. The electron density is calculated along the interatomic distance in a pseudopotential and a dispersion potential. Based on the measured and the calculated frequency shifts, we find the importance of attractive force in collisions to helium as well as heavy noble-gas atoms. Taking advantage of the simple energy structure of the Li atom, we obtain the s wave scattering length for free electrons on noble-gas atoms by using the hyperfine splitting frequency as a precise measure.
Ytterbium lattice frequency standard is an outstanding optical clock with a demonstrated relative frequency accuracy of 3.4·10-16, presently limited by the uncertainty on the blackbody radiation (BBR), lattice polarizabilities and cold collisions shifts. In particular the BBR shift is looming as a major component in the uncertainty budget of many optical frequency standards. In fact the uncertainty on BBR systematic shift in Ytterbium atoms is due both to experimental and theoretical limits in the knowledge of the atomic system: presently Ytterbium has the largest theoretical uncertainty on the BBR shift. Then, both for atomic physics and metrology, new measurements of the Ytterbium atomic properties are strongly demanded, such as the determination of transition matrix elements, lifetimes, branching ratios, polarizabilities and hyperfine constants. In this work we present a set of new measurements for the radiative decay and for the cold collisions trap losses in laser-cooled Ytterbium atoms. These data are relevant to the blackbody radiation shift evaluation and to the cold collisions shift theory.
Collisions with background gas particles can shift the resonance frequencies of atoms in atomic clocks. The internal quantum states of atoms can also become entangled with their motional states due to the recoil imparted by a collision, which leads to a further shift of the clock frequency through the relativistic Doppler shift. It can be complicated to evaluate the Doppler and collisional frequency shifts for clock atoms in such entangled states, but estimates of these shifts are essential in order to improve the accuracy of optical atomic clocks. We present a formalism that describes collisions and relativistic Doppler shifts in a unified manner, and can therefore be used to accurately estimate collisional frequency shifts in trapped-atom clocks.
Collisions with background gas can perturb the transition frequency of trapped ions in an optical atomic clock. We develop a nonperturbative framework based on a quantum channel description of the scattering process and use it to derive a master equation which leads to a simple analytic expression for the collisional frequency shift. As a demonstration of our method, we calculate the frequency shift of the Sr+{\mathrm{Sr}}^{+}Sr+ optical atomic clock transition due to elastic collisions with helium.
Collisions of atomic ions in optical clocks with background gas molecules result in systematic frequency shifts. We evaluate the frequency shift in Sr+{\mathrm{Sr}}^{+}Sr+ clocks due to collisions with helium atoms and hydrogen molecules, using ab initio spin-orbit-coupled potential energy surfaces together with a master equation for the collisional shift. Our results lead to improved uncertainty estimates for collisional frequency shifts in Sr+{\mathrm{Sr}}^{+}Sr+ optical clocks.