Analysis of thermal radiation in ion traps for optical frequency standards

Abstract

In many of the high-precision optical frequency standards with trapped atoms or ions that are under development to date, the AC Stark shift induced by thermal radiation leads to a major contribution to the systematic uncertainty. We present an analysis of the inhomogeneous thermal environment experienced by ions in various types of ion traps. Finite element models which allow the determination of the temperature of the trap structure and the temperature of the radiation were developed for 5 ion trap designs, including operational traps at PTB and NPL and further optimized designs. Models were refined based on comparison with infrared camera measurement until an agreement of better than 10% of the measured temperature rise at critical test points was reached. The effective temperature rises of the radiation seen by the ion range from 0.8 K to 2.1 K at standard working conditions. The corresponding fractional frequency shift uncertainties resulting from the uncertainty in temperature are in the 10 -18 range for optical clocks based on the Sr + and Yb + E2 transitions, and even lower for Yb + E3, In + and Al + . Issues critical for heating of the trap structure and its predictability were identified and design recommendations developed.

Atomic clocks for geodesy

“…As a consequence of its large mass, 2 nd order Doppler shifts are also reduced. Heating of the ion during the clock interrogation increases the uncertainty of these shifts which together with the evaluation of the BBR environment and the knowledge about the differential polarizability, are the major contributors to the clock inaccuracy (Doležal et al, 2015;Huntemann et al, 2016). Power broadening of the narrow clock transition by the clock laser results in significant ac Stark shifts that are nulled by a special pulse sequence called Hyper-Ramsey (Hobson et al, 2016;Huntemann et al, 2012a;Yudin et al, 2010;Zanon-Willette et al, 2016).…”

An optimized ion trap geometry to measure quadrupole shifts of 171 Yb + clocks

“…On the other hand, precision measurements with ions stored in a non-ideal trap, the anharmonic components of the potential Φ (k>2) (x, y, z) are non-negligible due to the fact that they change ion dynamics and also affect the systematics. For minimizing such effects several groups, such as, NPL UK [41], NRC Canada [11] and PTB Germany [42,43] have come up with different end cap trap designs for establishing single ion frequency standards. Here we aim to identify a new end cap trap geometry in which the trap induced quadrupole shift can be minimized.…”

Highly charged ions: Optical clocks and applications in fundamental physics

“…They offer moderately large motional frequencies of up to several MHz to allow recoilfree spectroscopy in the Lamb-Dicke regime while maintaining potentially low motional heating rates of only a few motional quanta per second (Brownnutt et al, 2015). Recently even linear multi-ion traps for precision spectroscopy and optical clocks have been developed (Doležal et al, 2015;Herschbach et al, 2012;Keller et al, 2016Keller et al, , 2015Pyka et al, 2014), with trap-induced shifts below 10 −19 fractional frequency uncertainty (Keller et al, 2017). While most single-ion frequency standards in the past are room temperature systems, with the notable exception of the Hg + clock (Rosenband et al, 2008), cryogenic Paul traps are mandatory for HCI to achieve a sufficiently long lifetime through excellent vacuum conditions (Schwarz et al, 2012).…”