An ultrastable optical clock based on neutral atoms trapped in an optical lattice is proposed. Complete control over the light shift is achieved by employing the 5s 2 1 S0 → 5s5p 3 P0 transition of 87 Sr atoms as a "clock transition". Calculations of ac multipole polarizabilities and dipole hyperpolarizabilities for the clock transition indicate that the contribution of the higher-order light shifts can be reduced to less than 1 mHz, allowing for a projected accuracy of better than 10 −17 .PACS numbers: 32.80. Pj, 42.50.Vk, 31.10.+z, 31.15.Ar, 31.15.Md, 32.70.Cs Careful elimination of perturbations on electronic states and of motional effects has been considered as a prerequisite for realizing an atom frequency standard [1]. A single ion trapped in an RF quadrupole field is one of the ideal systems that satisfy these requirements [2], as the trap prepares a quantum absorber completely at rest in free space for an extended time and its electric field vanishes at the center of the trap. Employing this scheme, quantum projection noise (QPN) limited spectroscopy [3] has been performed with an expected accuracy of 10 −18 [1,4].Despite its anticipated high accuracy, the stability of the single-ion based optical clock is severely limited by QPN; long averaging times are required to meet its ultimate accuracy [5]. The measure of the fractional instability is provided by the Allan variance, σ y (τ ) = 1Assuming the transition line Q ≈ 1.6 × 10 14 [4] and a cycle time of τ m ≈ 0.1 s, 4 × 10 7 measurement cycles are required for a single quantum absorber (N = 1) to reach σ y (τ ) = 10 −18 , corresponding to a total averaging time τ of a few months. For further increase of the stability, the averaging time increases quadratically and will become inordinately long.One may think of increasing the number of quantum absorbers N as employed in neutral atom based optical standards [6,7,8]. In this case, however, the atom-laser interaction time sets an upper bound for the Q-factor since an atom cloud in free space expands with finite velocity and is strongly accelerated by the gravity during the measurement. Hence the highest line Q ≈ 10 12 [6] obtained for neutral atoms is 2 orders of magnitude smaller than that of a trapped ion. Furthermore, it has been pointed out that residual Doppler shifts arising from an imperfect wavefront of the probe beam and atom-atom collisions during the measurement affect its ultimate accuracy [7,8].In this Letter, we discuss the feasibility of an "optical lattice clock" [9], which utilizes millions of neutral atoms separately confined in an optical lattice [10] that is designed to adjust the dipole polarizabilities α E1 for the probed electronic states in order to cancel light field perturbations on the measured spectrum [11]. In striking contrast with conventional approaches toward frequency standards [1], the proposed scheme interrogates atoms while they are strongly perturbed by an external field. We will show that this perturbation can be canceled out to below 10 −17 by carefully designing th...
We report vapor-cell magneto-optical trapping of Hg isotopes on the (1)S(0)-(3)P(1) intercombination transition. Six abundant isotopes, including four bosons and two fermions, were trapped. Hg is the heaviest nonradioactive atom trapped so far, which enables sensitive atomic searches for "new physics" beyond the standard model. We propose an accurate optical lattice clock based on Hg and evaluate its systematic accuracy to be better than 10;{-18}. Highly accurate and stable Hg-based clocks will provide a new avenue for the research of optical lattice clocks and the time variation of the fine-structure constant.
Recent progress in optical lattice clocks requires unprecedented precision in controlling systematic uncertainties at $10^{-18}$ level. Tuning of nonlinear light shifts is shown to reduce lattice-induced clock shift for wide range of lattice intensity. Based on theoretical multipolar, nonlinear, anharmonic and higher-order light shifts, we numerically demonstrate possible strategies for Sr, Yb, and Hg clocks to achieve lattice-induced systematic uncertainty below $1\times 10^{-18}$.Comment: 5 pages, 4 figure
We report a hitherto undiscovered frequency shift for forbidden J = 0-->J = 0 clock transitions excited in atoms confined to an optical lattice. These shifts result from magnetic-dipole and electric-quadrupole transitions, which have a spatial dependence in an optical lattice that differs from that of the stronger electric-dipole transitions. In combination with the residual translational motion of atoms in an optical lattice, this spatial mismatch leads to a frequency shift via differential energy level spacing in the lattice wells for ground state and excited state atoms. We estimate that this effect could lead to fractional frequency shifts as large as 10(-16), which might prevent lattice-based optical clocks from reaching their predicted performance levels. Moreover, these effects could shift the magic wavelength in lattice clocks in three dimensions by as much as 100 MHz, depending on the lattice configuration.
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