Maximizing the nondemolition nature of a quantum measurement via an adaptive readout protocol

TL;DR

This paper introduces an adaptive readout protocol for high-dimensional quantum systems that enhances measurement fidelity and reduces disturbance, crucial for fault-tolerant quantum computing.

Contribution

The authors develop a novel adaptive switching measurement protocol that minimizes measurement-induced errors in high-dimensional quantum systems, demonstrated on nuclear qudits in silicon.

Findings

Increased readout fidelity from 98.93% to 99.61%.

Reduced overall readout time by a factor of three.

Revealed nuclear spin flips due to hyperfine and quadrupole interactions.

Abstract

Quantum error correction (QEC) requires non-invasive measurements for fault tolerant quantum computing. Deviations from ideal quantum non-demolition (QND) measurements can disturb the encoded information. To address this challenge, we develop a readout protocol for a $D-$dimensional system that, after a single positive outcome, switches to probing only the $D{-}1$ remaining subspace. This adaptive switching strategy minimizes measurement-induced errors by relying on negative-result measurement results that do not perturb the Hamiltonian. We apply the protocol on an 8-dimensional $^{123}{\rm Sb}$ nuclear qudit in silicon, and achieve an increase in the readout fidelity from $(98.93\pm0.07)\%$ to $(99.61\pm0.04)\%$, while reducing threefold the overall readout time. To highlight the broader relevance of measurement-induced errors, we study a 10-dimensional $^{73}{\rm Ge}$ nuclear spin read out through Pauli spin blockade, revealing nuclear spin flips arising from hyperfine and quadrupole interactions. These results unveil the effect of non-ideal QND readout across diverse platforms, and introduce an efficient readout protocol that can be implemented with minimal FPGA logic on existing hardware.