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arXiv:1201.3544 · Physical Review Letters

Neutral Atom Frequency Reference in the Deep Ultraviolet with Fractional Uncertainty=5.7×10−15

John J. McFerran, L. Yi, Sinda Mejri, Sylvain Di Manno, W. Zhang, Jocelyne Guéna, Yann Le Coq, S. Bize

Published May 4, 2012• 101 citations
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Abstract

We present an assessment of the ($6{s}^{2}$) $^{1}S_{0}\ensuremath{\leftrightarrow}(6s6p)^{3}P_{0}$ clock transition frequency in $^{199}\mathrm{Hg}$ with an uncertainty reduction of nearly 3 orders of magnitude and demonstrate an atomic quality factor $Q$ of $\ensuremath{\sim}{10}^{14}$. The $^{199}\mathrm{Hg}$ atoms are confined in a vertical lattice trap with light at the newly determined magic wavelength of $362.5697\ifmmode\pm\else\textpm\fi{}0.0011\text{ }\text{ }\mathrm{nm}$ and at a lattice depth of $20{E}_{R}$. The atoms are loaded from a single-stage magneto-optical trap with cooling light at 253.7 nm. The high $Q$ factor is obtained with an 80 ms Rabi pulse at 265.6 nm. We find the frequency of the clock transition to be $1\text{ }128\text{ }575\text{ }290\text{ }808\text{ }162.0\ifmmode\pm\else\textpm\fi{}6.4(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{stat})\text{ }\text{ }\mathrm{Hz}$ (i.e., with $\mathrm{\text{fractional uncertainty}}=5.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$). Neither an atom number nor second order Zeeman dependence has yet been detected. Only three laser wavelengths are used for the cooling, lattice trapping, probing, and detection.

DOI
10.1103/physrevlett.108.183004

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We present an assessment of the (6s26{s}^{2}6s2) 1S0\ensuremath↔(6s6p)3P0^{1}S_{0}\ensuremath{\leftrightarrow}(6s6p)^{3}P_{0}1S0​\ensuremath↔(6s6p)3P0​ clock transition frequency in 199Hg^{199}\mathrm{Hg}199Hg with an uncertainty reduction of nearly 3 orders of magnitude and demonstrate an atomic quality factor QQQ of \ensuremath∼1014\ensuremath{\sim}{10}^{14}\ensuremath∼1014. The 199Hg^{199}\mathrm{Hg}199Hg atoms are confined in a vertical lattice trap with light at the newly determined magic wavelength of 362.5697\ifmmode±\else\textpm\fi0.0011  nm362.5697\ifmmode\pm\else\textpm\fi{}0.0011\text{ }\text{ }\mathrm{nm}362.5697\ifmmode±\else\textpm\fi0.0011  nm and at a lattice depth of 20ER20{E}_{R}20ER​. The atoms are loaded from a single-stage magneto-optical trap with cooling light at 253.7 nm. The high QQQ factor is obtained with an 80 ms Rabi pulse at 265.6 nm. We find the frequency of the clock transition to be 1 128 575 290 808 162.0\ifmmode±\else\textpm\fi6.4(syst)\ifmmode±\else\textpm\fi0.3(stat)  Hz1\text{ }128\text{ }575\text{ }290\text{ }808\text{ }162.0\ifmmode\pm\else\textpm\fi{}6.4(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{stat})\text{ }\text{ }\mathrm{Hz}1 128 575 290 808 162.0\ifmmode±\else\textpm\fi6.4(syst)\ifmmode±\else\textpm\fi0.3(stat)  Hz (i.e., with fractional uncertainty=5.7\ifmmode×\else\texttimes\fi10\ensuremath−15\mathrm{\text{fractional uncertainty}}=5.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}fractional uncertainty=5.7\ifmmode×\else\texttimes\fi10\ensuremath−15). Neither an atom number nor second order Zeeman dependence has yet been detected. Only three laser wavelengths are used for the cooling, lattice trapping, probing, and detection.
We report on the Lamb-Dicke spectroscopy of the doubly forbidden (6s(2))(1)S(0)↔(6s6p)(3)P(0) transition in (199)Hg atoms confined to a vertical 1D optical lattice. With lattice trapping of ≲10(3) atoms and a 265.6 nm probe laser linked to the LNE-SYRTE primary frequency reference we have determined the center frequency of the transition for a range of lattice wavelengths and at two lattice trap depths. We find the Stark-free (magic) wavelength to be 362.53(0.21) nm-essential knowledge for future use of this line in a clock with anticipated 10(-18) range accuracy. We also present evidence of the laser excitation of a Wannier-Stark ladder of states in a lattice of well depth 10E(R).
We present details on the ultraviolet lattice spectroscopy of the (6sss2{}^{2}2) 1{}^{1}1SSS${}_{0}\ensuremath{\leftrightarrow}$ (6$s666p$) 3{}^{3}3PPP0{}_{0}0​ transition in neutral mercury, specifically 199{}^{199}199Hg. Mercury atoms are loaded into a one-dimensional vertically aligned optical lattice from a magneto-optical trap with an rms temperature of $\ensuremath{\sim}$60 $\ensuremath{\mu}$K. We describe aspects of the magneto-optical trapping, the lattice cavity design, and the techniques employed to trap and detect mercury in an optical lattice. The clock-line frequency dependence on lattice depth is measured at a range of lattice wavelengths. We confirm the magic wavelength to be 362.51(0.16) nm. Further observations to those reported by Yi et al. [Phys. Rev. Lett. 106, 073005 (2011)] are presented regarding the laser excitation of a Wannier-Stark ladder of states.
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 calculations assessing the ultimate precision of an atomic clock based on the 578 nm $6{}^{1}{S}_{0}\ensuremath{\rightarrow}6{}^{3}{P}_{0}$ transition in Yb atoms confined in an optical lattice trap. We find that this transition has a natural linewidth less than 10 mHz in the odd Yb isotopes, caused by hyperfine coupling. The shift in this transition due to the trapping light acting through the lowest order ac polarizability is found to become zero at the magic trap wavelength of about 752 nm. The effects of Rayleigh scattering, multipole polarizabilities, vector polarizability, and hyperfine induced electronic magnetic moments can all be held below 1 mHz (about one part in 1018).{10}^{18}).1018). In the case of the hyperpolarizability, however, larger shifts due to nearly resonant terms cannot be ruled out without an accurate measurement of the magic wavelength.
We report the experimental measurement of a magic wavelength at 476.823 62(8) nm for the ${}^{88}\mathrm{Sr}\phantom{\rule{0.2em}{0ex}}5{s}^{2}{\phantom{\rule{0.1em}{0ex}}}^{1}{\mathrm{S}}_{0}\ensuremath{\rightarrow}5s5p{\phantom{\rule{0.1em}{0ex}}}^{3}{\mathrm{P}}_{0}$ clock transition. The magic wavelength is determined through an ac Stark shift spectroscopy of atoms in an optical dipole trap. The value is in reasonable agreement with the theoretical prediction, differing by 0.061(54) nm. This magic wavelength, being shorter than the commonly used one at 813 nm, will be important for applications such as Bragg-pulse matter-wave interferometry involving both clock states. This work also paves the way for quantum simulation with a shorter lattice constant.
State-of-the-art optical clocks based on neutral atoms have already surpassed the world's best microwave atomic clocks in both accuracy and stability, paving the way to high-precision measurements of elementary aspects of nature, like the search for the drift of fundamental constants or the application of relativistic geodesy.These clocks operate with ensembles trapped in an optical lattice.Normally, high-power trapping laser fields induce a large AC Stark shift on the clock's transition frequency, as the clock states have different polarizabilities.A key feature of lattice clocks is the magic wavelength, for which the atomic polarizabilities of the clock states are equal, therefore compensating a differential frequency shift on the clock transition.In the periodic potential of the optical lattice, the energy spectrum of motional states features a band structure, analogous to electrons in a crystalline structure well-known from solid state physics.Within this band structure, atoms can tunnel between adjacent lattice sites.As a consequence from tunneling motion, the clock transition experiences a frequency shift and a broadening, which becomes pronounced in the shallow lattice regime.This work presents the first demonstration of a 24 Mg optical lattice clock including the precise determination of the frequency of the clock transition, its magic wavelength and its second-order Zeeman shift.Furthermore, the effect of tunneling in an optical lattice for magnesium has been extensively studied via optical spectroscopy of Bloch bands and substantiated with theoretical models, that were initially developed for a strontium optical lattice clock.Measuring lattice light induced frequency shifts of the clock transition for various lattice wavelengths and intensities, yielded a value of the magic wavelength of the 1 S 0 → 3 P 0 clock transition in 24 Mg of 468.463(207) nm.This value is in well agreement with a recent theoretical calculation of 468.45(23) nm, using a refined atomic structure model.The experimental value for the magic wavelength was independently verified with optical spectroscopy of Bloch bands carried out on the clock transition.Here, the AC Stark modified band structure is directly probed by a single frequency scan of the carrier resonance, featuring an asymmetric line shape, that is strongly dependent on the lattice wavelength.This technique demonstrates a novel method for the determination of the magic wavelength and could also be applied to other atomic species.In bosonic isotopes of alkaline earth(-like) elements, like 24 Mg, optical dipole excitation of the spin-forbidden 1 S 0 → 3 P 0 clock transition can be enhanced, e.g. by applying an external magnetic field.While these bosons are insensitive to first-order Zeeman shifts, the second-order Zeeman effect displays a dominant contribution to the clock's error budget.In this thesis, the magnetic polarizability β is measured to be -206.6(2.0)MHz/T 2 , consistent with a theoretical calculation, and the clock transition frequency was found to be 655 058 646 691(101) kHz.