Doppler-free spectroscopy of the 1S0-3P0 optical clock transition in laser-cooled fermionic isotopes of neutral mercury

TL;DR

This paper reports the first direct Doppler-free laser spectroscopy of the 1S0-3P0 transition in fermionic neutral mercury isotopes, achieving highly precise frequency measurements that improve upon previous data and highlight mercury's potential for optical lattice clocks.

Contribution

First direct Doppler-free spectroscopy of the 1S0-3P0 transition in fermionic mercury isotopes with high-precision frequency determination using a femtosecond laser comb.

Findings

Resolved Doppler-free recoil doublet enabling precise frequency measurement

Achieved frequency uncertainties below Doppler-broadened linewidth

Measured transition frequencies with over 10,000-fold improvement in accuracy

Abstract

We have performed for the first time direct laser spectroscopy of the 1S0-3P0 optical clock transition at 265.6 nm in fermionic isotopes of neutral mercury laser-cooled in a magneto-optical trap. Spectroscopy is performed by measuring the depletion of the magneto-optical trap induced by the excitation of the long-lived 3P0 state by a probe at 265.6 nm. Measurements resolve the Doppler-free recoil doublet allowing for a determination of the transition frequency to an uncer- tainty well below the Doppler-broadened linewidth. We have performed absolute measurement of the frequency with respect to an ultra-stable reference monitored by LNE-SYRTE fountain pri- mary frequency standards using a femtosecond laser frequency comb. The measured frequency is 1128575290808 +/- 5.6 kHz in 199Hg and 1128569561140 +/- 5.3 kHz in 201Hg, more than 4 orders of magnitude better than previous indirect determinations. Owing to a low sensitivity to blackbody radiation, mercury is a promising candidate for reaching the ultimate performance of optical lattice clocks.