High-fidelity indirect readout of trapped-ion hyperfine qubits

TL;DR

This paper introduces a high-fidelity indirect readout protocol for trapped-ion hyperfine qubits, mapping qubit states to a different ion species using laser Raman transitions, achieving low error rates and avoiding decoherence.

Contribution

The work presents a novel indirect readout method that enhances fidelity and robustness in trapped-ion qubits by using Raman transitions and state partitioning.

Findings

Readout errors as low as 1.2e-4 and below 1e-5

Robustness to spontaneous photon scattering

Avoids decoherence of spectator qubits

Abstract

We propose and demonstrate a protocol for high-fidelity indirect readout of trapped ion hyperfine qubits, where the state of a $^9\text{Be}^+$ qubit ion is mapped to a $^{25}\text{Mg}^+$ readout ion using laser-driven Raman transitions. By partitioning the $^9\text{Be}^+$ 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 $1.2^{+1.1}_{-0.6} \times 10^{-4}$ and $0^{+1.9}_{-0} \times 10^{-5}$ with 68% confidence while avoiding decoherence of spectator qubits due to stray resonant light that is inherent to direct fluorescence detection.