Converting leakage errors to erasure errors and coherence preserving cooling in alkaline-earth neutral atoms*

Neutral atoms are a prominent platform for quantum computation, as they are easily scalable, have reconfigurable geometry and can perform parallel high-fidelity entangling gates. A major source of errors in neutral atom systems is leakage out of computational subspace, either due to atom-loss, or decay to other metastable states. This noise is detrimental for fault-tolerant computation as they are not Pauli errors and need special error correction protocols. In this work, we develop a scheme to convert leakage errors into erasure errors for information encoded in nuclear spin of  ⁸⁷Sr. Another problem with neutral atom quantum computation is that cooling protocols do not preserve information stored in atoms. This prevents us from implementing large depth circuits, as qubit operations heat up atoms. In this work, we also developed a scheme to cool ⁸⁷Sr atoms while preserving qubit coherence. The excited ¹P₁ manifold can be used for both imaging and sideband cooling of these atoms. The hyperfine interaction in this manifold leads to optical pumping between nuclear spin levels, which destroys the quantum information stored in the ground-state. We use the AC Stark shift to decouple the electronic and nuclear degrees of freedom in this manifold. This takes out the “which way information” about the nuclear spin state in the scattered photons, letting us image the atoms and cool them, without disturbing the encoded information. These advances could significantly improve the prospects of neutral atoms for fault tolerant computation.