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

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 ${}^{123}\mathrm{Sb}$ nuclear qudit in silicon, and achieve an increase in the readout fidelity from $(98.93\pm 0.07)\%$ to $(99.61\pm 0.04)\%$, while reducing threefold the overall readout time. To highlight the broader relevance of measurement-induced errors, we study a 10-dimensional ${}^{73}\mathrm{Ge}$ 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.

Main text: 10 pages, 5 figures. Supplementary Material: 7 pages, 5 figures

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