Professor Christopher Foot

Abstract:

The leading experimental determinations of the fine-structure constant 𝛼 currently rely on atomic photon-recoil measurements from Ramsey-Bordé atom interferometry with large-momentum transfer to provide an absolute mass measurement. We propose an experimental scheme for an intermediate-scale differential atom interferometer to measure the photon recoil of neutral atomic species with a single-photon optical clock transition. We calculate trajectories for our scheme that optimize the recoil phase while nullifying the undesired gravity-gradient phase by considering independently launching two clouds of ultracold atoms with the appropriate initial conditions. For Sr and Yb, we find an atom interferometer of height 3 m to be sufficient for an absolute mass measurement precision of 𝛥⁢𝑚/𝑚∼1×10−11 with current technology. Such a precise measurement would halve the current uncertainty in 𝛼 — an uncertainty that would no longer be limited by an absolute mass measurement. The removal of this limitation would allow the current uncertainty in 𝛼 to be reduced by a factor of 10 by corresponding improvements in relative mass measurements, thus paving the way for higher-precision tests of the standard model of particle physics.

Abstract:

We report on developments in the atomic fountain systems being built and operated at NPL. An improved generation of Cs fountains has been developed, with units being constructed for use by both NPL and commercial customers. These systems combine world-class stability and accuracy with increased reliability and can run for long periods of time without maintenance. Here we describe how the NPL fountains work, and present performance data for the latest systems. We describe some of the applications of these fountains, both in time scale implementation and fundamental science. We also present an overview of a miniature atomic fountain that is being developed, which will help make fountain technology accessible to a wider range of sectors.