Potential of electric quadrupole transitions in radium isotopes for single-ion optical frequency standards

Abstract

We explore the potential of the electric quadrupole transitions 7s 2 S 1/2 -6d 2 D 3/2 , 6d 2 D 5/2 in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive A Ra + candidates, with A = 223-229, are identified. In particular, we show that the transition 7s 2 S 1/2 (F = 2,m F = 0)-6d 2 D 3/2 (F = 0,m F = 0) at 828 nm in 223 Ra + , with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of 10 −17 . With more experimental effort, the 223,225,226 Ra + clocks could be pushed to a projected performance reaching the 10 −18 level.

Towards a precise measurement of atomic parity violation in a single Ra + ion

“…We note here that the very same setup which is used for a competitive APV measurement is also well suited for the realization of a single ion optical clock based on Ra + [25]. The isotope 223 Ra is of particular interest.…”

“…Here the sensitivity to the quadrupole shifts in the 7s 2 S 1/2 -6d 2 D 3/2 transitions-which is a major systematic effect limiting present single ion clocks-is minimal. Whereas for the APV measurement the light shift needs to measured as a function of laser intensity very accurately, a clock only requires its stable control [25]. A stability of 10 −18 or beyond appears feasible for a 223 Ra + clock, which makes it very competitive with present clocks.…”

Hyperfine structure of the level in trapped short-lived 211, 209Ra+ ions

“…Trapped Ra + isotopes are also outstanding candidates for high stability clocks [5]. A detailed understanding of the atomic structure of Ra + is indispensable for such high-precision experiments.…”

Compilation of Spectroscopic Data of Radium (Ra I and Ra II)

“…The reasons are: large polarizability due to the near degeneracy of the opposite parity 7s7p 3 P 0 1 and 7s6d 3 D 2 levels; some isotopes of radium have nuclear octupole deformation; and high atomic number (Z = 88). Singly ionized radium ion is proposed as a promising candidate for atomic parity violation experiments and as an atomic clock [31][32][33] . In this context, short lived radioactive isotopes were produced at the TRIµP facility, University of Groningen, The Netherlands 34 .…”