Measurement of the Rydberg constant with cold Rydberg atoms

Andira Ramos, Kaitlin Moore, Georg A. Raithel

Andira Ramos, Kaitlin Moore, Georg A. Raithel

Georg A. Raithel, Ryan Cardman, Alisher Duspayev

Rydberg atoms are highly excited atoms that have large sensitivities to external fields, lending these atoms extraordinary characteristics for fundamental high-precision spectroscopy as well as for electromagnetic-field sensing applications. Recent results on high-precision spectroscopy with cold Rydberg atoms in modulated optical lattices are presented. The discussed approach can serve as a platform for fundamental-physics studies, which include a model-insensitive measurement of the Rydberg constant and a search for wave-like dark matter. As an example for the utility of Rydberg atoms in field sensing applications, an experiment is presented in which the linear Stark effect of cold Rydberg atoms is employed to measure electric fields in cold ion clouds, demonstrating that Rydberg laser spectroscopy allows electrode-free, non-invasive plasma diagnostics.

Georg A. Raithel

Georg A. Raithel, Andira Ramos, Kaitlin Moore +1 more

A measurement of the Rydberg constant using cold circular Rydberg atoms is proposed. Since these atoms have long lifetimes, negligible quantum electrodynamics and no nuclear-overlap corrections, the measurement can shed new light on the “proton radius puzzle”. The atoms are trapped in an optical lattice. Transitions are driven using a lattice-modulation technique to perform Doppler-free sub-THz spectroscopy; the transition frequencies yield the Rydberg constant. The selected transitions are free of first-order Zeeman and Stark shifts. Systematic uncertainties due to lattice-induced shifts, core-polarization, second-order Zeeman and Stark shifts, etc are estimated.

Kaitlin Moore

Using cold atoms, I probe the energy-level intervals between Rydberg states to high spectroscopic precision. The focus of this work is to lay the groundwork for an updated, highly-controlled measurement of the Rydberg constant using circular-state Rydberg atoms, needed to resolve a recent conflict in proton-radius values that arose in 2010 (the so-called 'proton radius puzzle'). Toward this end, I have demonstrated a fundamentally-new mechanism with which to drive atomic (Rydberg-Rydberg) transitions, utilizing an inelastic (state-changing) ponderomotive interaction. Until now, the multipole-field interaction has been the sole mechanism on which spectroscopy of atomic transitions has been based. In this work, the state-changing ponderomotive interaction ('ponderomotive spectroscopy') is demonstrated by amplitude-modulating an optical standing wave at a transition resonance of a Rydberg atom. At the core of this new spectroscopic technique is the requirement that the light intensity must be modulated in space within the atomic volume, and in time at the desired atomic transition frequency. A Rydberg atom in a modulated optical lattice is very well-suited for a demonstration of this novel type of spectroscopy. Magic-wavelength conditions of this interaction are also identified, as well as a method to drive transitions at harmonics of the modulation. Both of these features of ponderomotive spectroscopy will be utilized to simultaneously trap and probe Rydberg atoms to perform the Rydberg constant measurement. I also present a high-precision measurement of the quantum defect of a high-angular-momentum state of rubidium, the atomic species that will be used in the Rydberg constant measurement. The quantum defects of high-angular-momentum states are needed to determine the effect of the rubidium core polarizability on the Rydberg constant measurement, which is anticipated to be a leading uncertainty. Finally, I present the background and design work for a measurement of the Rydberg constant specifically tailored to help resolve the proton radius puzzle, thereby completing the major preliminary work needed for the performance of that high-precision measurement.