Time-optimal robust quantum control for partially known errors
Abstract
Robust quantum control usually assumes one of two extremes: the error is of a known form and only its strength is unknown, or nothing at all is known about it. In practice one often sits in between. The size of a static error is unknown, but its class is known, for example, it only shifts energy levels, or it acts on each subsystem separately. We ask how fast a control can cancel, to first order, every error in such a class. A time-independent Hamiltonian can do this if and only if all errors in the class have zero diagonal in a common basis. In that case an equally spaced energy ladder in this basis does it after one period. A lower bound that holds for any time-dependent control with bounded drive power shows that this simple constant control is optimal for several natural classes, including unknown level shifts and unknown local errors on two subsystems. Completely unknown errors need a time-dependent control, and there, knowing the error class shortens the minimum time by a factor √ d 2 + 1. So partial knowledge of the error changes not only how long an optimal robust control takes, but also its form.
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BibTeX
@misc{gaggioli2026timeoptimal,
title = {{Time-optimal robust quantum control for partially known errors}},
author = {Llorenç Balada Gaggioli},
howpublished = {HAL},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.21596},
eprint = {2610.21596},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05804137v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Time-optimal robust quantum control for partially known errors
AU - Llorenç Balada Gaggioli
PY - 2026
DA - 2026/10/15
PB - HAL
DO - 10.48550/arxiv.2610.21596
UR - https://hal.science/hal-05804137v1
AB - Robust quantum control usually assumes one of two extremes: the error is of a known form and only its strength is unknown, or nothing at all is known about it. In practice one often sits in between. The size of a static error is unknown, but its class is known, for example, it only shifts energy levels, or it acts on each subsystem separately. We ask how fast a control can cancel, to first order, every error in such a class. A time-independent Hamiltonian can do this if and only if all errors in the class have zero diagonal in a common basis. In that case an equally spaced energy ladder in this basis does it after one period. A lower bound that holds for any time-dependent control with bounded drive power shows that this simple constant control is optimal for several natural classes, including unknown level shifts and unknown local errors on two subsystems. Completely unknown errors need a time-dependent control, and there, knowing the error class shortens the minimum time by a factor √ d 2 + 1. So partial knowledge of the error changes not only how long an optimal robust control takes, but also its form.
ER -