Measuring multipole moments of the CPT density matrix during optical polarization modulation

Abstract

Chip-scale atomic clocks (CSACs) based on Coherent Population Trapping (CPT) are at the forefront of next-generation timekeeping for diverse applications, including global navigation satellite systems (GNSS), satellite communications, cell-phone networks, and hand-held GNSS receivers. Notwithstanding the potential ubiquity of this atomic device, a performance-limiting aspect of CSACs is the vapor-phase signal-to-noise ratio (SNR) of their ground-state (mF = 0 to mF = 0) atomic hyperfine resonance. Specifically, in commercially available devices angular-momentum optical pumping “pushes” atomic population towards high |mF| Zeeman sublevels at the expense of population in the 0-0 clock transition. Though mitigation strategies for this SNR limiting process have been proposed and demonstrated there has, to date, been little direct measurement of the population distribution among Zeeman sub-states for atoms undergoing CPT, and how that population distribution is altered by SNR improving mitigation strategies. Here, we describe our initial studies examining this question.