Mid-circuit ground-state cooling and ancilla readout in the $\textit{omg}$ architecture

Abstract

The trapped-ion optical-metastable-ground ($\textit{omg}$) architecture for quantum processors promises the full functionality of two-species experiments, including sympathetic cooling and non-destructive ancilla readout, without the corresponding hardware overhead. We confirm that we can cool a global motional mode of a mixed metastable-ground state Coulomb crystal to the motional ground state via dissipative operations on the ground ($\textit{g}$) qubit without disturbing coherence of the metastable ($\textit{m}$) qubit. This enables quantum logic spectroscopy to non-destructively readout the state of the $\textit{m}$ qubit using fluorescence detection of the $\textit{g}$ qubit. Extensions of these demonstrations to larger system sizes should enable the mitigation of motional heating after ion shuttling and syndrome extraction for quantum error correction, both crucial primitives for future fault-tolerant quantum computers based on trapped ions.