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arXiv · 2605.03187

Operating a bistable qubit

Fabrizio Berritta·Jan A. Krzywda·Tom Dvir·Paul Buttles·Stanislav Eilhart·Jeroen Danon·Ferdinand Kuemmeth
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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 from 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.

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Fabrizio Berritta, Jan A. Krzywda, Tom Dvir, Paul Buttles, Stanislav Eilhart, Jeroen Danon, Ferdinand Kuemmeth. 2026-05-04. Operating a bistable qubit. https://arxiv.org/abs/2605.03187

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