Stability enhancement of atomic timekeeping using Raman adiabatic rapid passage

Abstract

Current state-of-the-art atomic clocks span the range from large accurate fountain clocks such as the NIST-F2 to relatively small inaccurate chip scale clocks. Small clocks with higher accuracy could greatly expand the range of applications for precision timekeeping, and enable cheaper implementation of existing applications. This type of clock may be realized by use of optical Raman interferometry based on pulsed interrogation of cold atoms. However, this method suffers from serious systematic error sources, e.g., AC Stark shift and Zeeman shift, which alter the atomic resonance frequency. A new method based on adiabatic rapid passage (ARP) has been recently demonstrated at Draper which has significantly reduced phase sensitivity to differential AC Stark shift. It is found that compared to standard Raman, use of ARP enhances timekeeping stability by a factor of three with stability of 2 x 10⁻¹² at 100 seconds. Increasing data rate may also improve short term stability. With all of the above improvements, ARP enhances short term fractional stability to 7 x 10⁻¹² at one second.