Anneal-path correction in flux qubits

Quantum annealers require accurate control and optimized operation schemes to reduce noise levels, in order to eventually demonstrate a computational advantage over classical algorithms. We study a high coherence four-junction capacitively shunted flux qubit (CSFQ), using dispersive measurements to...

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Bibliographic Details
Published in:npj quantum information 2021-02, Vol.7 (1), p.1-8, Article 36
Main Authors: Khezri, Mostafa, Grover, Jeffrey A., Basham, James I., Disseler, Steven M., Chen, Huo, Novikov, Sergey, Zick, Kenneth M., Lidar, Daniel A.
Format: Article
Language:English
Subjects:
639/766/1130/1064
639/766/483/2802
639/766/483/481
Annealing
Asymmetry
Classical and Quantum Gravitation
Computer applications
Noise reduction
Physics
Physics and Astronomy
Quantum Computing
Quantum Field Theories
Quantum Information Technology
Quantum Physics
Relativity Theory
Spintronics
String Theory
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Summary:Quantum annealers require accurate control and optimized operation schemes to reduce noise levels, in order to eventually demonstrate a computational advantage over classical algorithms. We study a high coherence four-junction capacitively shunted flux qubit (CSFQ), using dispersive measurements to extract system parameters and model the device. Josephson junction asymmetry inherent to the device causes a deleterious nonlinear cross-talk when annealing the qubit. We implement a nonlinear annealing path to correct the asymmetry in situ, resulting in a substantial increase in the probability of the qubit being in the correct state given an applied flux bias. We also confirm the multi-level structure of our CSFQ circuit model by annealing it through small spectral gaps and observing quantum signatures of energy level crossings. Our results demonstrate an anneal-path correction scheme designed and implemented to improve control accuracy for high-coherence and high-control quantum annealers, which leads to an enhancement of success probability in annealing protocols.
ISSN:2056-6387
2056-6387
DOI:10.1038/s41534-021-00371-9