Operating a bistable qubit
Abstract
Parasitic two-level-system (TLS) defects limit the stability and performance of solid-state quantum processors. Their interaction with a qubit can cause discrete, stochastic shifts of the qubit frequency, making the qubit bistable. We experimentally demonstrate an adaptive protocol for operating a bistable qubit with high fidelity using a classical controller powered by a field-programmable gate array (FPGA). Our "1-bit feedback" protocol estimates the qubit's bistable frequency and corrects the control frame using only one single-shot measurement, reaching the information limit set by the qubit's intrinsic entropy. We validate the protocol in a superconducting qubit by suppressing TLS-induced Ramsey beating, and deploy it to stabilize gate fidelities over time with approximately 136 kHz estimation bandwidth and a 77% error reduction. Our approach provides a simple, yet fundamentally efficient strategy for mitigating dephasing errors induced by strongly coupled TLS defects, and may enable the operation of large future qubit arrays suffering from few remaining, discrete instabilities.
Versions
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BibTeX
@misc{berritta2026operating,
title = {{Operating a bistable qubit}},
author = {Fabrizio Berritta and Jan A. Krzywda and Tom Dvir and Paul Buttles and Stanislav Eilhart and Jeroen Danon and Ferdinand Kuemmeth},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2605.03187},
eprint = {2605.03187},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.03187},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Operating a bistable qubit
AU - Fabrizio Berritta
AU - Jan A. Krzywda
AU - Tom Dvir
AU - Paul Buttles
AU - Stanislav Eilhart
AU - Jeroen Danon
AU - Ferdinand Kuemmeth
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2605.03187
UR - https://arxiv.org/abs/2605.03187
AB - Parasitic two-level-system (TLS) defects limit the stability and performance of solid-state quantum processors. Their interaction with a qubit can cause discrete, stochastic shifts of the qubit frequency, making the qubit bistable. We experimentally demonstrate an adaptive protocol for operating a bistable qubit with high fidelity using a classical controller powered by a field-programmable gate array (FPGA). Our "1-bit feedback" protocol estimates the qubit's bistable frequency and corrects the control frame using only one single-shot measurement, reaching the information limit set by the qubit's intrinsic entropy. We validate the protocol in a superconducting qubit by suppressing TLS-induced Ramsey beating, and deploy it to stabilize gate fidelities over time with approximately 136 kHz estimation bandwidth and a 77% error reduction. Our approach provides a simple, yet fundamentally efficient strategy for mitigating dephasing errors induced by strongly coupled TLS defects, and may enable the operation of large future qubit arrays suffering from few remaining, discrete instabilities.
ER -