Operating a bistable qubit

arXiv (Cornell University)

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.

Authors 7

1. Fabrizio Berritta

   University of Regensburg · Massachusetts Institute of Technology

   Affiliation as printed

   ) Institute of Experimental and Applied Physics , University of Regensburg , 93040 Regensburg , Germany

   ) Research Laboratory of Electronics , Massachusetts Institute of Technology , Cambridge , MA 02139 , USA

2. Jan A. Krzywda

   Center for Theoretical Physics · Instituto de Física Teórica

   Affiliation as printed

   ) Lorentz Institute for Theoretical Physics &

3. Tom Dvir
   Affiliation as printed

   ) Q.M Technologies Ltd. (Quantum Machines) 5) Qolab , Madison , Wisconsin 53706 , USA

4. Paul Buttles Aachen Leiden Institute of Advanced Computer Science

   Leiden University · University of Applied Sciences Leiden

   Affiliation as printed

   Leiden Institute of Advanced Computer Science , Universiteit Leiden , 2311 EZ Leiden , The Netherlands

5. Stanislav Eilhart Aachen Leiden Institute of Advanced Computer Science

   Leiden University · University of Applied Sciences Leiden

   Affiliation as printed

   Leiden Institute of Advanced Computer Science , Universiteit Leiden , 2311 EZ Leiden , The Netherlands

6. Jeroen Danon

   Norwegian University of Science and Technology

   Affiliation as printed

   ) Department of Physics , Norwegian University of Science and Technology , NO-7491 Trondheim , Norway

7. Ferdinand Kuemmeth