Upper Limit on the Magnetic Dipole Contribution to the 5p-8p Transition in Rb by Use of Ultracold Atom Spectroscopy

TL;DR

This study uses ultracold atom spectroscopy to set a new, more stringent upper limit on the magnetic dipole contribution to a specific forbidden transition in rubidium, refining previous measurements and theoretical expectations.

Contribution

The paper provides the first hyperfine-resolved measurement that constrains the magnetic dipole contribution to the 5p-8p transition in rubidium, improving the upper limit by a factor of about 50.

Findings

Upper limit on M1 transition strength is 50 times smaller than previous estimate.

Calculated M1 matrix element is below the experimental upper limit.

Spectroscopy distinguishes M1 from electric-quadrupole contributions in ultracold rubidium.

Abstract

We report on hyperfine-resolved spectroscopic measurements of the electric-dipole forbidden 5$p_{3/2} \to 8p_{1/2}$ transition in a sample of ultracold $^{87}$Rb atoms. The hyperfine selection rules enable the weak magnetic-dipole (M1) contribution to the transition strength to be distinguished from the much stronger electric-quadrupole (E2) contribution. An upper limit on the M1 transition strength is determined that is about 50 times smaller than an earlier experimental determination. We also calculate the expected value of the M1 matrix element and find that it is less than the upper limit extracted from the experiment.