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Proceedings of the ... annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting/Proceedings of a meeting - Precise Time and Time Interval (PTTI) Systems and Applications Meeting

Robust Optical Clocks Based on Alkaline-Earth Vapor Cells

Jordan L. Armstrong, N. Lemke, Kyle W. Martin, Christopher Erickson

Published Feb 26, 2016• 1 citation
Publisher

Abstract

Alkaline-earth atoms offer spectrally narrow transitions that are attractive for optical frequency standards. Thus far, experiments have been limited to laser-cooled and atomic beam geometries. We present compact vapor cell solutions for realizing high-performance single-laser alkaline-earth clocks that are simple in design.
DOI
10.33012/2016.13157

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A sharp resonance line that appears in three-photon transitions between the 1S0 and 3P0 states of alkaline earth and Yb atoms is proposed as an optical frequency standard. This proposal permits the use of the even isotopes, in which the clock transition is narrower than in proposed clocks using the odd isotopes and the energy interval is not affected by external magnetic fields or the polarization of trapping light. With this method, the width and the rate of the clock transition can, in principle, be continuously adjusted from the MHz level to sub-mHz without loss of signal amplitude by varying the intensities of the three optical beams. Doppler and recoil effects can be eliminated by proper alignment of the three optical beams or by point confinement in a lattice trap. Light-shift effects on the clock accuracy can be limited to below a part in 10(18).
Optical atomic clocks provide exceptionally accurate and precise signals for timekeeping and precision measurements, but they require high-power, free-space laser configurations that limit scalability. We introduce and explore a scalable infrastructure for strontium (Sr) optical-lattice clocks that incorporates co-design of atomic-beam slowing and a magneto-optical trap (MOT) from an effusion source, generation of complex, three-dimensional free-space laser configurations with a photonic integrated circuit (PIC) and metasurface (MS) optics, and laser stabilization to a frequency-comb supercontinuum generated with integrated nonlinear photonics. With these elements, we realize MOTs of all stable strontium isotopes (84^{84}84Sr, 86^{86}86Sr, 87^{87}87Sr, 88^{88}88Sr) with populations commensurate with natural abundances, demonstrating precise beam control and robustness. Access to laser-cooled alkaline-earth atoms with scalable integrated photonics enables system engineering for optical clocks, quantum sensing, and quantum information, and our experiments demonstrate extensible technologies that advance toward a Sr optical clock largely free of bulk optics.
We describe a high-performance, compact optical frequency standard based on a microfabricated Rb vapor cell and a low-noise, external cavity diode laser operating on the Rb two-photon transition at 778 nm. The optical standard achieves an instability of 1.8 × 10 − 13 τ − 1 / 2 for times less than 100 s and a flicker noise floor of 1 × 10 − 14 out to 6000 s. At long integration times, the instability is limited by variations in optical probe power and the ac Stark shift. The retrace was measured to 5.7 × 10 − 13 after 30 h of dormancy. Such a simple, yet high-performance optical standard could be suitable as an accurate realization of the meter or, if coupled with an optical frequency comb, as a compact atomic clock comparable to a hydrogen maser.