High-Fidelity Readout of Trapped-Ion Qubits

Abstract

We demonstrate single-shot qubit readout with a fidelity sufficient for fault-tolerant quantum computation. For an optical qubit stored in ${}^{40}\mathrm{Ca}^{+}$ we achieve 99.991(1)% average readout fidelity in ${10}^6$ trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in $145\mu \mathrm{s}$ average detection time. For ${}^{43}\mathrm{Ca}^{+}$, we propose and implement an optical pumping scheme to transfer a long-lived hyperfine qubit to the optical qubit, capable of a theoretical fidelity of 99.95% in $10\mu \mathrm{s}$. We achieve 99.87(4)% transfer fidelity and 99.77(3)% net readout fidelity.