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Chinese Optics Letters

Observation of the 1S0–3P0 optical clock transition in cold 199Hg atoms

Xiaohu Fu, Su Fang, Ru-Chen Zhao, Yanjie Zhang, Junchao Huang Junchao Huang, Jianfang Sun, Zhen Xu Zhen Xu, Yuzhu Wang Yuzhu Wang

Published Jan 1, 2018• 5 citations
Publisher

Abstract

We report on the observation of the highly forbidden 1S0–3P0 optical clock transition in laser-cooled 199Hg atoms. More than 95% depletion of cold 199Hg atoms is detected in the magneto-optical trap. Using the free-of-field detection method, the AC Stark shift from the cooling laser is removed from the in-field spectroscopy. At low-power clock laser pumping, the linewidth of the clock spectroscopy is approximately 450 kHz (full width at half-maximum), which corresponds to a Doppler broadening at the atom temperature of 60 μK. We determine the 1S0–3P0 transition frequency to be 1,128,575,290.819(14) MHz by referencing with a hydrogen maser and measuring with a fiber optical frequency comb. Moreover, a weak Doppler-free signal is observed.

DOI
10.3788/col201816.060202

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We report on the observation of the highly forbidden 1S0–3P0 optical clock transition in laser-cooled 199Hg atoms. More than 95% depletion of cold 199Hg atoms is detected in the magneto-optical trap. Using the free-of-field detection method, the AC Stark shift from the cooling laser is removed from the in-field spectroscopy. At low-power clock laser pumping, the linewidth of the clock spectroscopy is approximately 450 kHz (full width at half-maximum), which corresponds to a Doppler broadening at the atom temperature of 60 μK. We determine the 1S0–3P0 transition frequency to be 1,128,575,290.819(14) MHz by referencing with a hydrogen maser and measuring with a fiber optical frequency comb. Moreover, a weak Doppler-free signal is observed.
We report the direct excitation of the highly forbidden (6s2) 1S0 <--> (6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.
Direct observation and frequency measurement of /sup 1/S/sub 0//spl rarr//sup 3/P/sub 0 /line within an accuracy of 20 kHz is reported. The resonance frequency with an accuracy of /spl sim/ 100 kHz is reported by indirect measurement of the energy difference between /sup 1/S/sub 0/ and /sup 3/P/sub 0/ states. It is performed by successive frequency measurements of atomic transitions with higher linewidth, easier to observe: /sup 1/S/sub 0/ - /sup 3/P/sub 1/, /sup 3/P/sub 1/ - /sup 3/S/sub 1/ and /sup 3/S/sub 1/ - /sup 3/P/sub 0/ transitions. To perform direct observation of the clock transition, atoms are cooled to a temperature of /spl sim/ 2 mK in a magneto-optical trap (MOT). Although the saturation broadening of the transition is orders of magnitude smaller than the Doppler width (1.5 MHz), a detectable signal is achieved by inducing a small leak in the MOT with a laser tuned to resonance. Atoms accumulate in the metastable /sup 3/P/sub 0 /state where they escape the trap. The resonance is detected by a decrease in the MOT fluorescence signal with a contrast of 1%.
Clock transition at 1.14μm1.14 \mu \mathrm{m}1.14μm in neutral thulium is a promising candidate for compact and robust transportable optical clock due to its extremely low sensitivity to external electric and magnetic fields. Cold Tm atoms are now used in optical lattice clocks, quantum simulators and for the study of Bose-Einstein condensation and cold collision physics. In this work, we discuss experimentally measured absolute frequencies of the two transitions at 410.6 nm and 530.7 nm, used for laser cooling of thulium atoms, transition at 418.8 nm used for optical pumping and clock transition at 1140 nm. Using accurate laser spectroscopy in an ensemble of cold thulium atoms, we measured frequencies of these transitions using an optical frequency comb, which was referenced to an active hydrogen maser. Transition frequencies were measured with an uncertainty at one tenth of their natural linewidth, which is sufficient for cooling and pumping of thulium atoms. The uncertainty of the clock transition frequency is 30 Hz, which was limited by the maser frequency calibration with GNSS. Our results can find application in existing experiments with cold thulium atoms and especially in new projects.
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We report spectroscopy of the 1S 0 - 3P 0 clock transition in neutral 174Yb atoms confined to a one-dimensional optical lattice at the ac Stark shift-canceling wavelength of 759.35 nm. Spectroscopic linewidths as narrow as 4 Hz, full width at half-maximum, are shown with good contrast and signal-to-noise ratios. An upper limit on frequency instability is demonstrated to be 3 × 10−15 at one second by measuring with respect to another stable laser through a Ti:sapphire femtosecond laser frequency comb.