Coherent Control of the Fine-Structure Qubit in a Single Alkaline-Earth Atom

TL;DR

This paper demonstrates the first coherent control of a novel qubit in a single strontium atom using metastable states, achieving millisecond coherence times and paving the way for advanced neutral atom quantum computing.

Contribution

It introduces a new qubit encoding in metastable states of $^{88}$Sr atoms, with demonstrated coherent control and potential for rapid quantum gate operations.

Findings

Achieved Rabi oscillations with 17 THz energy gap using phase-locked lasers.

Measured qubit coherence time of 1.2 ms under magic trapping conditions.

Identified noise sources limiting coherence and suggested future improvements.

Abstract

We report on the first realization of a novel neutral atom qubit encoded in the metastable fine-structure states ${^3\rm{P}_0}$ and ${^3\rm{P}_2}$ of single $^{88}$Sr atoms trapped in an optical tweezer. Raman coupling of the qubit states promises rapid single-qubit rotations on par with the fast Rydberg-mediated two-body gates. We demonstrate preparation, read-out, and coherent control of the qubit. In addition to driving Rabi oscillations bridging an energy gap of more than 17 THz using a pair of phase-locked clock lasers, we also carry out Ramsey spectroscopy to extract the transverse qubit coherence time $T_2$. When the tweezer is tuned into magic trapping conditions, which is achieved in our setup by tuning the tensor polarizability of the ${^3\rm{P}_2}$ state via an external control magnetic field, we measure $T_2 = 1.2$ ms. A microscopic quantum mechanical model is used to simulate our experiments including dominant noise sources. We identify the main constraints limiting the observed coherence time and project improvements to our system in the immediate future. Our work opens the door for a so far unexplored qubit encoding concept for neutral atom based quantum computing.