High-fidelity, adaptive qubit measurements through repetitive information transfer

TL;DR

This paper demonstrates high-fidelity, adaptive qubit measurements using repetitive information transfer and quantum nondemolition detection with trapped ions, achieving 99.94% fidelity and enabling efficient multi-qubit spectroscopy.

Contribution

It introduces a novel adaptive measurement protocol based on repetitive information transfer, significantly reducing error rates in qubit detection.

Findings

Achieved 99.94% measurement fidelity for a single qubit.

Developed a technique for adaptive multi-qubit measurement with a single ancilla.

Applied the method to spectroscopy of an optical clock transition.

Abstract

Using two trapped ion species ($\rm{^{27}Al^+}$ and $\rm{^9Be^+}$) as primary and ancillary systems, we implement qubit measurements based on the repetitive transfer of information and quantum nondemolition detection. The repetition provides a natural mechanism for an adaptive measurement strategy, which leads to exponentially lower error rates compared to using a fixed number of detection cycles. For a single qubit we demonstrate 99.94 % measurement fidelity. We also demonstrate a technique for adaptively measuring multiple qubit states using a single ancilla, and apply the technique to spectroscopy of an optical clock transition.