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arXiv:2105.10401

Measurement of the probe Stark shift of the 87Sr optical lattice clock using the frequency modulation spectroscopy

Qinfang Xu, Xiaotong Lu, Jingjing Xia, Yebing Wang, Hong Chang

Published May 21, 2021• 0 citations
arXivHTMLPDF

Abstract

With the uncertainty of the optical clocks improving to the order of 10-18, the probe light used to detect the clock transition has demonstrated nonnegligible Stark shift, provoking to precisely evaluate this shift. Here, we demonstrate a frequency modulation technique to realize a large measurement lever arm of the probe Stark shift with no cost of the measurement accuracy of the interleaved stabilization method. This frequency-modulated spectrum is theoretical described and experimental verified. The probe Stark shift coefficient of the 87Sr optical lattice clock is experimentally determined as -(45.97+/-3.51) Hz/(W/cm2) using this frequency modulation spectroscopy.

DOI
10.48550/arxiv.2105.10401

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With the uncertainty of the optical clocks improving to the order of 10-18, the probe light used to detect the clock transition has demonstrated nonnegligible Stark shift, provoking to precisely evaluate this shift. Here, we demonstrate a frequency modulation technique to realize a large measurement lever arm of the probe Stark shift with no cost of the measurement accuracy of the interleaved stabilization method. This frequency-modulated spectrum is theoretical described and experimental verified. The probe Stark shift coefficient of the 87Sr optical lattice clock is experimentally determined as -(45.97+/-3.51) Hz/(W/cm2) using this frequency modulation spectroscopy.
In this paper, we demonstrate a frequency modulation technique to accurately measure the probe Stark shift of optical clocks. The effective coupling strength of the probe laser to the clock transition is precisely controlled by this frequency modulation technique, which is different from the traditional method by controlling the effective coupling strength via changing the probe light power. In an 87Sr optical lattice clock, the probe Stark shifts are measured as a function of the square of the bare state coupling strength. The probe Stark shift coefficient of 87Sr is experimentally determined as −6.0(5)×10−7/Hz using this frequency modulation technique. With the help of frequency modulation, the probe light power can be as large as possible without decreasing the measurement precision and the achieved measurement lever arm is improved by more than one order of magnitude compared with previous results.
Abstract We investigate Floquet modulation for measuring the probe-induced AC Stark shift coefficient in optical lattice clocks. Periodic frequency modulation allows a high probe intensity to enlarge the measured frequency difference between the settings at low and high probe power while Bessel function dressing maintains a narrow excitation spectrum. This combination improves sensitivity to the coefficient without sacrificing frequency discrimination. We identify modulation conditions that suppress additional frequency shifts while avoiding strong motional resonances. At the same probe intensities and total measurement time, numerical simulations including preparation time show a lower coefficient uncertainty than conventional Rabi inter-rogation with a single π pulse. At high probe intensities, the Floquet coefficient uncertainty approaches a plateau dominated by Rabi frequency calibration.
We describe our experiment which evaluates frequency shifts due to collisions in a 1-D optical lattice clock with88Sr. The atoms in the lattice are probed on the1S0-3P0transition which is highly forbidden but becomes weakly allowed by applying a static homogeneous magnetic field which mixes3P1to the3P0state. Using the method of interleaved stabilization, we have quantified the density dependent shift of the88Sr clock transition. By knowing the coefficient of the shift we can determine optimum conditions under which a 1-D lattice clock with88Sr can be operated with a fractional accuracy of 10-16.
In this paper, the magic wavelength of the 87Sr optical lattice clock is determined by a method that bypasses the need for lattice trap depth modulation. Instead, it relies on an additional AC Stark shift generated by a dipole beam operating near the frequency of the lattice light and oriented perpendicular to the optical lattice. The magic wavelength is inferred by measuring the AC Stark shift induced by the dipole beam as a function of its power under various frequency detunings. The effect of the dipole beam on the external states of the cold ensemble is evaluated through comparative analysis of the radial and axial sideband spectra, both with and without the dipole beam. Variations in density shift resulting from changes in external states are evaluated using comprehensive numerical calculations. By avoiding trap depth modulation, this method effectively suppresses the influence of the density shift, thereby offering a promising avenue for accurately determining the magic wavelength.
A major obstacle for optical clocks is the frequency shift due to black body radiation. We discuss how one can tackle this problem in an optical lattice clock; in our case 87-Sr: firstly, by a measurement of the dc Stark shift of the clock transition and, secondly, by interrogating the atoms in a cryogenic environment. Both approaches rely on transporting ultracold atoms over several cm within a probe cycle. We evaluate this approach of mechanically moving the optical lattice and conclude that it is feasible to transport the atoms over 50 mm within 300 ms. With this transport a dc Stark shift measurement will allow to reduce the contribution of the blackbody radiation to the fractional uncertainty below 2 * 10^-17 at room temperature by improving the shift coefficient known only from atomic structure calculations up to now. We propose a cryogenic environment at 77 K that will reduce this contribution to few parts in 10^-18.
We experimentally investigate an optical clock based on ;{171}Yb (I = 1/2) atoms confined in an optical lattice. We have evaluated all known frequency shifts to the clock transition, including a density-dependent collision shift, with a fractional uncertainty of 3.4 x 10;{-16}, limited principally by uncertainty in the blackbody radiation Stark shift. We measured the absolute clock transition frequency relative to the NIST-F1 Cs fountain clock and find the frequency to be 518 295 836 590 865.2(0.7) Hz.