General Methods for Suppressing the Light Shift in Atomic Clocks Using Power Modulation

V.I Yudin,Z.L Newman,J Kitching,E.A Donley,M Shuker,J.W Pollock,R Boudot,A Hansen,M.T Hummon,A.V Taichenachev,M Yu Basalaev

doi:10.1103/physrevapplied.14.024001

Abstract

We show that the light shift in atomic clocks can be suppressed using time variation of the interrogation field intensity. By measuring the clock output at two intensity levels, error signals can be generated that simultaneously stabilize a local oscillator to an atomic transition and correct for the shift of this transition caused by the interrogating optical field. These methods are suitable for optical clocks using one- and two-photon transitions, as well as for microwave clocks based on coherent population trapping or direct interrogation. The proposed methods can be widely used both for high-precision scientific instruments and for a wide range of commercial clocks, including chip-scale atomic clocks.

Highlights

Atomic clocks have had broad impact in both fundamental physics and practical applications
While the two-loop power modulation (PM)-autocompensate the light shift (ACS) is more complicated to implement than the single-loop PM-combined error signal (CES), it requires fewer constraints, as outlined below. Both the PM-CES and the PM-ACS methods can be applied in optical clocks using one-photon and two-photon spectroscopy, as well as in rf clocks based on coherent population trapping (CPT) resonances and optical pumping clocks
We note that the PM-ACS method can be considered conceptually as a PM analog of one of the variants of generalized autobalanced Ramsey spectroscopy given in Refs. [18,21], in which an additional frequency shift was used as the concomitant parameter

Summary

INTRODUCTION

Atomic clocks have had broad impact in both fundamental physics and practical applications. Understanding, and suppressing, this light shift is important in improving the long-term frequency stability of these types of references Particular successes in this direction have been achieved over the past decade for atomic clocks based on Ramsey spectroscopy. A method has been proposed that can suppress the light shift for two-photon spectroscopy on the transition (5s2S1/2) ↔ (5d2D5/2) in 87Rb through the use of two interrogating laser fields at different frequencies [34]. We develop two methods for suppressing the light shift and its fluctuation in atomic clocks based on either cw or Ramsey spectroscopy Both methods use a power modulation (PM) with sequential alternating operations with two different laser powers P1 and P2. Both the PM-CES and the PM-ACS methods can be applied in optical clocks using one-photon and two-photon spectroscopy, as well as in rf clocks based on CPT resonances and optical pumping clocks

GENERAL DESCRIPTION OF THE LIGHT SHIFT IN ATOMIC CLOCKS

PM-ACS for stepwise modulation of power

PM-ACS for low frequency harmonic modulation of power

CONCLUSION