Ultrastable Optical Clock with Neutral Atoms in an Engineered Light Shift Trap

Abstract

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...

Absolute frequency measurement of the ${{}^{1}}{{\text{S}}_{0}}$ – ${{}^{3}}{{\text{P}}_{0}}$ transition of171Yb

“…In optical lattice clocks thousands of neutral atoms are trapped in an optical potential at the light induced Stark shift cancellation (magic) wavelength [22]. Optical lattice fre quency standards have now demonstrated systematic fractional uncertainties at the 10 −17 -10 −18 level [5] and also an unprec edented frequency stability [23] opening the path for frequency comparisons beyond the uncertainty of the realization of the SI units in hundreds of seconds [24].…”

Laser sources for precision spectroscopy on atomic strontium

“…The error signal has then S/N ∼ 200 on a bandwidth of 3 MHz. The error signal for locking the laser to the cavity is then sent to the laser via three channels: (1) to the PZT of the external cavity of the laser with a bandwidth up to 2 kHz; (2) to the laser current driver with a bandwidth up to 50 kHz; (3) directly to the diode with a bandwidth up to 3 MHz.…”

“…Strontium has become the object of recent study in atomic physics ranging from frequency metrology [1] to cold collisions [2] and multiple scattering [3].…”

Optical Lattice Polarization Effects on Hyperpolarizability of Atomic Clock Transitions

“…In recent years significant attention has been devoted to optical lattice atomic clocks [1,2], in part because the prospects for a fractional frequency uncertainty of such a clock could achieve of the level 10 −17 -10 −18 . Apart from obvious practical applications, such improved clocks will be critical for a variety of terrestrial and space-borne applications including improved tests of the basic laws of physics and searches for drifts in the fundamental constants [3].…”

“…Here apart from long-term stabilization of the laser radiation (power, transverse distribution of intensity) we need precision long-term stability of the whole optical system. A significant reduction of a lattice field intensity is not an effective solution of the problem, because in this case both the number and lifetime of the trapped atoms will be reduced also.Thus, the hyperpolarizability effect on atoms in optical lattices is an important physical problem, which needs to be carefully studied (the papers [1,6,8] have begun such investigations). In this context the search for alternative methods of minimization of the second-order shifts is especially relevant.…”