arXiv subjects

William McGehee

Publications and source records attributed to William McGehee.

4 recordsLinked to original sources

arXiv2026

Controlling light shifts in chip-scale atomic beam clocks

Chip-scale atomic beam clocks are being investigated to extend the range of clock stability achievable in low-power timing applications. Here, we demonstrate a centimeter-scale, Ramsey coherent population trapping (CPT) clock based on a microfabricated Cs atomic beam device and investigate the interplay between light shifts and Doppler shifts that determines its leading clock systematics. We show that these shifts exhibit competing dependencies on CPT light parameters, leading to ``doubly-insensitive" operating points where the clock frequency is simultaneously insensitive to laser frequency and power. We further demonstrate a method for controlling key clock shifts using spectroscopic signatures from the atomic beam that is compatible with fully-integrated operation. The clock achieves a fractional frequency stability of $2 \times 10^{-10}$ at $1~\textrm{s}$ and sub-$\mu$s drift over nearly $17~\textrm{hours}$, with leading CPT light systematics controlled below the $10^{-12}$ level.

physics.atom-ph↗

arXiv2025

Doppler Shift Mitigation in a Chip-Scale Atomic Beam Clock

Chip-scale microwave atomic systems based on thermal atomic beams offer a promising approach to realize low-power and low-drift clocks for timing holdover applications. Miniature beam clocks are expected to suppress many of the shifts that commonly limit existing chip-scale atomic clocks based on coherent population trapping, including collisional shifts and some light shifts. However, the beam geometry can amplify some challenges such as Doppler shifts, which generate a strong sensitivity to laser frequency variation. Using a cm-scale 87Rb atom beam clock, we identify a surprisingly strong competition between Doppler shifts and resonant light shifts arising from asymmetric decay in the clock spectroscopy {\Lambda}-system. Leveraging this competition between Doppler and resonant light shifts, we demonstrate clock operation at specific, convenient experimental parameters consistent with zero sensitivity to laser frequency variation and white-noise-limited clock frequency averaging for 1000 s of integration.

physics.atom-ph↗

arXiv2025

Wavefront Mapping for Absolute Atom Interferometry

Wavefront distortions are a leading source of systematic uncertainty in light-pulse atom interferometry, limiting absolute measurements of gravitational acceleration at the 30 nm/s$^2$ level. Here, we demonstrate in situ spatially resolved measurement of the interferometer phase in a Mach-Zehnder atom interferometer as a tool to characterize and correct wavefront bias. By introducing controllable curvature of the Raman light using an adjustable collimation retro-reflector, we show that the bias due to parabolic wavefront curvature can be measured with 1 mrad uncertainty and that finite-size corrections impact the measured phase curvature. This measurement process could be adopted in optimized atom interferometer gravimeters to reduce wavefront bias uncertainty below the nm/s$^2$ level.

physics.atom-ph↗

arXiv2018

Bad-Metal Relaxation Dynamics in a Fermi Lattice Gas

We report the discovery of phenomena consistent with bad-metal relaxation dynamics in the metallic regime of an optical-lattice Hubbard model. The transport lifetime induced by inter-particle scattering for a mass current of atoms excited by stimulated Raman transitions is measured, and the corresponding analog of resistivity is inferred. By exploring a range of temperature, we demonstrate incompatibility with weak-scattering theory and a key characteristic of bad metals: anomalous resistivity scaling consistent with $T$-linear behavior. We also observe the onset of two behaviors---incoherent transport and the approach to the Mott-Ioffe-Regel limit---associated with bad metals. The interaction and temperature scaling of resistivity are verified to be consistent with dynamic mean-field theory (DMFT) predictions of a bad metal, which is associated with the reduction of quasiparticle weight by strong interactions.

cond-mat.quant-gas↗