1201.6631 (Z. Zuhrianda et al.)

Anomalously small blackbody radiation shift in Tl+ frequency standard    [PDF]

Z. Zuhrianda, M. S. Safronova, M. G. Kozlov

The operation of atomic clocks is generally carried out at room temperature,
whereas the definition of the second refers to the clock transition in an atom
at absolute zero. This implies that the clock transition frequency should be
corrected in practice for the effect of finite temperature of which the leading
contributor is the blackbody radiation (BBR) shift. In the present work, we
used configuration interaction + coupled-cluster method to evaluate
polarizabilities of the $6s^2 ^1S_0$ and $6s6p ^3P_0$ states of Tl$^+$ ion; we
find $\alpha_0(^1S_0)=19.6$ a.u. and $\alpha_0(^3P_0)=21.4$ a.u.. The resulting
BBR shift of the $6s6p ^3P_0 - 6s^2 ^1S_0$ Tl$^+$ transition at $300 K$ is
$\Delta \nu_{\rm BBR}=-0.0157(16)$ Hz. This result demonstrates that near
cancelation of the $^1S_0$ and $^3P_0$ state polarizabilities in divalent B+,
Al+, In$^+$ ions of group IIIB [Safronova \textit{et al.}, PRL 107, 143006
(2011)] continues for much heavier Tl$^+$, leading to anomalously small BBR
shift for this system. This calculation demonstrates that the BBR contribution
to the fractional frequency uncertainty of the Tl+ frequency standard at 300K
is $1\times10^{-18}$. We find that Tl+ has the smallest fractional BBR shift
among all present or proposed frequency standards with the exception of Al+.

View original: http://arxiv.org/abs/1201.6631