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arXiv:2112.11556 · Physical Review A

Magneto-optical trapping of mercury at high phase-space density

Quentin Lavigne, Thorsten Groh, Simon Stellmer

Published Mar 15, 2022• 11 citations
arXivHTMLPDF

Abstract

We present a realization of a magneto-optical trap of mercury atoms on the $^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{1}$ intercombination line. We report on trapping of all stable mercury isotopes. We characterize the effect of laser detuning, laser intensity, and gradient field on the trapping performance of our system. The atom number for the most abundant isotope $^{202}\mathrm{Hg}$ is $5\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms. Moreover, we study the difference in cooling processes for bosonic and fermionic isotopes. We observe agreement with the Doppler cooling theory for the bosonic species and show sub-Doppler cooling for the fermionic species. We reach a phase-space density of a few parts in ${10}^{\ensuremath{-}7}$, which constitutes a promising starting condition for dipole trap loading and evaporative cooling.

DOI
10.1103/physreva.105.033106

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 18, 2014•0 citations
We present a realization of a magneto-optical trap of mercury atoms on the 1S0\ensuremath→3P1^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{1}1S0​\ensuremath→3P1​ intercombination line. We report on trapping of all stable mercury isotopes. We characterize the effect of laser detuning, laser intensity, and gradient field on the trapping performance of our system. The atom number for the most abundant isotope 202Hg^{202}\mathrm{Hg}202Hg is 5\ifmmode×\else\texttimes\fi1075\ifmmode\times\else\texttimes\fi{}{10}^{7}5\ifmmode×\else\texttimes\fi107 atoms. Moreover, we study the difference in cooling processes for bosonic and fermionic isotopes. We observe agreement with the Doppler cooling theory for the bosonic species and show sub-Doppler cooling for the fermionic species. We reach a phase-space density of a few parts in 10\ensuremath−7{10}^{\ensuremath{-}7}10\ensuremath−7, which constitutes a promising starting condition for dipole trap loading and evaporative cooling.
Laser cooling and trapping of neutral mercury is performed in a single-stage (1)S(0)↔(3)P(1) 3D magneto-optical trap. We give a detailed account of the atom cloud size and temperature for both bosonic ((200)Hg and (202)Hg) and fermionic ((199)Hg and (201)Hg) isotopes. The bosonic isotope temperatures are in close agreement with Doppler cooling theory, while temperatures obtained for the fermionic isotopes are lower, suggesting the presence of sub-Doppler cooling. A minimum temperature of 29±4 μK is achieved for (201)Hg.
This thesis explores the development and application of laser-cooled mercury atoms for precision measurements relevant to fundamental physics. A primary motivation is the search for a permanent electric dipole moment in mercury, that could shed light on the baryon asymmetry of the universe. We present the design and construction of a custom experimental apparatus for producing and trapping cold mercury atoms, detailing challenges associated with working with mercury in an ultra-high vacuum environment and considering deep-ultraviolet optics. A magneto-optical trap operating on the 1S0-3P1 intercombination line at 254 nm is realized for all seven stable isotopes, achieving atom numbers up to 5x107 and phase-space densities up to 1x10-6 suitable for optical dipole trap loading. Cooling efficiency for all bosonic and fermionic isotopes are characterized over a wide parameter space, and we show sub-Doppler cooling in 199Hg and 201Hg. The successful loading of mercury into a high-power optical dipole trap is demonstrated, forming the basis for future electric dipole moment experiments of laser cooled mercury atoms. Prospects of evaporatively cooling mercury down to quantum degeneracy could allow for a quantum-enhanced metrology tool kit for the planned measurements. Apart from this, we are exploring the use of ultracold fermionic gases made of mercury as a quantum simulator for impurity physics. As a promising versatile and tunable platform for studying impurity-bath interactions, we are assessing the feasibility of observing Friedel oscillations in ultracold quantum gases.Further, we perform precision isotope shift spectroscopy on several dipole-allowed atomic transitions in mercury. Via King plot analysis this allows investigations of the mercury nuclear structure – also relevant for electric dipole moment bounds – and lays the foundation for probing a potential fifth force carrier coupling electrons to neutrons. We also propose upgrades to the machine for improvements in laser cooling, extensions of the spectroscopy search and a proposed experimental setup for probing the atomic electric dipole moment in an optical dipole trap of cold mercury atoms.
We report the magneto-optical trapping of ytterbium atoms using the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{3}{P}_{1}$ intercombination transition. The magneto-optical trap is continuously loaded from an atomic beam decelerated by a Zeeman-tuned atomic-beam slower operated at the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{1}{P}_{1}$ transition. Among seven stable isotopes of ytterbium, six isotopes of170Yb,\mathrm{of}{ }^{170}\mathrm{Y}\mathrm{b},of170Yb, 171Yb,{}^{171}\mathrm{Yb},171Yb, 172Yb,{}^{172}\mathrm{Yb},172Yb, 173Yb,{}^{173}\mathrm{Yb},173Yb, 174Yb,{}^{174}\mathrm{Yb},174Yb, and 176Yb{}^{176}\mathrm{Yb}176Yb are successfully trapped. The number and density of the trapped atoms are about 108{10}^{8}108 and ${10}^{11} {\mathrm{cm}}^{\ensuremath{-}3},$ respectively. The temperature of atoms is estimated to be about $20 \ensuremath{\mu}\mathrm{K}$ from the time-of-flight measurement. The decay time of the trapped atoms after stopping the loading of atoms is about 3 s.
We report direct laser spectroscopy of the $^{1}S_{0}\mathrm{\text{\ensuremath{-}}}^{3}P_{0}$ transition at 265.6 nm in fermionic isotopes of neutral mercury in a magneto-optical trap. Measurements of the frequency against the LNE-SYRTE primary reference using an optical frequency comb yield $1\text{ }128\text{ }575\text{ }290\text{ }808.4\ifmmode\pm\else\textpm\fi{}5.6\text{ }\text{ }\mathrm{kHz}$ in 199Hg^{199}\mathrm{Hg}199Hg and $1\text{ }128\text{ }569\text{ }561\text{ }139.6\ifmmode\pm\else\textpm\fi{}5.3\text{ }\text{ }\mathrm{kHz}$ in 201Hg^{201}\mathrm{Hg}201Hg. The uncertainty, allowed by the observation of the Doppler-free recoil doublet, is 4 orders of magnitude lower than previous indirect determinations. Mercury is a promising candidate for future optical lattice clocks due to its low sensitivity to blackbody radiation.
We report narrow-line laser cooling and trapping of strontium atoms down to the photon recoil temperature. 88Sr{}^{88}\mathrm{Sr}88Sr atoms precooled by the broad $^{1}S_{0}\ensuremath{-}^{1}P_{1}$ transition at 461 nm were further cooled in a magneto-optical trap using the spin-forbidden transition $^{1}S_{0}\ensuremath{-}^{3}P_{1}$ at 689 nm. We have thus obtained an atomic sample with a density over ${10}^{12}\mathrm{cm}{}^{\ensuremath{-}3}$ and a minimum temperature of 400 nK, corresponding to a maximum phase space density of ${10}^{\ensuremath{-}2}$ which is 3 orders of magnitude larger than the value that has been obtained by magneto-optical traps to date. This scheme provides us an opportunity and system to study quantum statistical properties of degenerate fermions as well as bosons.
Mercury is the heaviest stable atom that could be laser cooled, and have a large nuclear charge number. So it has a distinct advantage in quantum precision measurement such as fine-structure constant α and permanent electric dipole moment. Due to its insensitivity of black body radiation, atomic mercury is a good candidate of optical clock. Here we report our recent development of laser cooling of neutral mercury atom. By cooling the mercury source to about -70°C, an ultra-high vacuum system was realized to produce ultracold mercury atoms. The commercial frequency quadrupled semiconductor laser is locked on the cooling transition (1S0-3P1 transition, wavelength of 253.7 nm) by sub-Doppler frequency modulation spectroscopy. By the modification with feed-forward method, the UV laser becomes faster tunable and more stable. A folded beam configuration was used to realize the magneto-optical trap (MOT) because of the shortage of cooling laser power, and the ultracold mercury atoms were observed by fluorescence detection. All of six rich abundant isotopes have been observed, and the atom number is about 1.5×106 with density of 3.5×109 /cm3 for 202Hg. With optical shutter and the programmable system to control the time sequence, the temperature of ultracold atoms can be measured by time of flight method. To enhance the laser power, a 1014.8 nm fiber laser amplifier was developed, which can work at room temperature. After two stages of frequency doubling, about 75 mW of 253.7 nm UV laser were generated, and the saturated absorption spectroscopy of mercury atom was also observed. More power of UV laser could help to trap more atoms in the future. These works laid a good foundation to realize the mercury lattice clock.