High-fidelity readout of trapped-ion qubits

TL;DR

This paper demonstrates high-fidelity, single-shot readout of trapped-ion qubits, achieving near-perfect fidelity in optical and hyperfine states, crucial for fault-tolerant quantum computing.

Contribution

It introduces a highly accurate readout method for trapped-ion qubits, including an adaptive measurement technique and a robust optical pumping scheme for hyperfine states.

Findings

Achieved 99.991% fidelity for optical qubit readout.

Implemented a transfer scheme with 99.77% fidelity for hyperfine qubits.

Demonstrated rapid, reliable qubit state detection within 145 microseconds.

Abstract

We demonstrate single-shot qubit readout with fidelity sufficient for fault-tolerant quantum computation, for two types of qubit stored in single trapped calcium ions. For an optical qubit stored in the (4S_1/2, 3D_5/2) levels of 40Ca+ we achieve 99.991(1)% average readout fidelity in one million trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in 145us average detection time. For a hyperfine qubit stored in the long-lived 4S_1/2 (F=3, F=4) sub-levels of 43Ca+ we propose and implement a simple and robust optical pumping scheme to transfer the hyperfine qubit to the optical qubit, capable of a theoretical fidelity 99.95% in 10us. Experimentally we achieve 99.77(3)% net readout fidelity, inferring at least 99.87(4)% fidelity for the transfer operation.