Bang-bang protocol for nondispersive qubit readout
Abstract
Fast, precise, and quantum-non-demolition (QND) readout of superconducting qubits is a fundamental component of high-fidelity quantum sensing and computation. Conventional approaches typically operate in the dispersive regime, where the qubit-resonator coupling g is weak compared to the detuning Δ. While exhibiting good QND properties, the readout rate is limited to ∼ g2√N/Δ≪ g, where N is the number of photons in the resonator. QND readout in the nondispersive regime, where the readout rate reaches its full potential ∼ g, relies on parameter sweeps that may encounter resonances, leading to measurement-induced state transitions (MIST). In this work, we study a nondispersive readout protocol that replaces these sweeps by sudden quenches of the coupling constant, using a resonator that is preloaded with photons. We call this protocol bang-bang readout, and show that it realizes single-shot projective measurements. The fidelity and QNDness of the qubit post-measurement are remarkably high, with an error that decreases like 1/N. We show that the protocol can also be implemented without preloading the resonator by instead strongly driving the qubit, e.g., with a classical flux drive.
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BibTeX
@misc{ser2026bangbang,
title = {{Bang-bang protocol for nondispersive qubit readout}},
author = {Nina del Ser and Yinan Chen and Jacob Steiner and Gil Refael},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.23681},
eprint = {2608.23681},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.23681},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Bang-bang protocol for nondispersive qubit readout
AU - Nina del Ser
AU - Yinan Chen
AU - Jacob Steiner
AU - Gil Refael
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2608.23681
UR - https://arxiv.org/abs/2608.23681
AB - Fast, precise, and quantum-non-demolition (QND) readout of superconducting qubits is a fundamental component of high-fidelity quantum sensing and computation. Conventional approaches typically operate in the dispersive regime, where the qubit-resonator coupling g is weak compared to the detuning Δ. While exhibiting good QND properties, the readout rate is limited to ∼ g^2√N/Δ≪ g, where N is the number of photons in the resonator. QND readout in the nondispersive regime, where the readout rate reaches its full potential ∼ g, relies on parameter sweeps that may encounter resonances, leading to measurement-induced state transitions (MIST). In this work, we study a nondispersive readout protocol that replaces these sweeps by sudden quenches of the coupling constant, using a resonator that is preloaded with photons. We call this protocol bang-bang readout, and show that it realizes single-shot projective measurements. The fidelity and QNDness of the qubit post-measurement are remarkably high, with an error that decreases like 1/N. We show that the protocol can also be implemented without preloading the resonator by instead strongly driving the qubit, e.g., with a classical flux drive.
ER -