We propose and demonstrate a protocol for high-fidelity indirect readout of trapped ion hyperfine qubits, where the state of a 9Be+ qubit ion is mapped to a 25Mg+ readout ion using laser-driven Raman transitions. By partitioning the 9Be+ ground state hyperfine manifold into two subspaces representing the two qubit states and choosing appropriate laser parameters, the protocol can be made robust to spontaneous photon scattering errors on the Raman transitions, enabling repetition for increased readout fidelity. We demonstrate combined readout and back-action errors for the two subspaces of 1.2−0.6+1.1×10−4 and 0−0+1.9×10−5 with 68% confidence while avoiding decoherence of spectator qubits due to stray resonant light that is inherent to direct fluorescence detection.
@article{arxiv.2112.06341,
title = {High-fidelity indirect readout of trapped-ion hyperfine qubits},
author = {Stephen D. Erickson and Jenny J. Wu and Pan-Yu Hou and Daniel C. Cole and Shawn Geller and Alex Kwiatkowski and Scott Glancy and Emanuel Knill and Daniel H. Slichter and Andrew C. Wilson and Dietrich Leibfried},
journal= {arXiv preprint arXiv:2112.06341},
year = {2022}
}