Faraday rotation of a tightly focussed beam from a single trapped atom

TL;DR

This paper demonstrates Faraday rotation caused by a single trapped atom using a tightly focused laser beam, enabling high-fidelity state read-out and phase-shift measurements with implications for quantum sensing.

Contribution

It introduces a method to observe Faraday rotation from a single atom with high precision, advancing quantum measurement techniques.

Findings

Achieved polarization rotation detection from a single atom.

Measured phase-shift related to electromagnetically-induced transparency.

Demonstrated 98% fidelity in atomic state read-out.

Abstract

Faraday rotation of a laser field induced by a single atom is demonstrated by tightly focussing a linearly polarized laser beam onto a laser-cooled ion held in a harmonic Paul trap. The polarization rotation signal is further used to measure the phase-shift associated with electromagnetically-induced-transparency and to demonstrate read-out of the internal state on the qubit transition with a detection fidelity of 98 $\pm$ 1%. These results have direct implications for single atom magnetometery and dispersive read-out of atomic superpositions.