[Joint CQSE & NCTS Special Seminar] ​Hamiltonian Phase Error in Resonantly Driven CNOT Gate Above the Fault-Tolerant Threshold

Title: [Joint CQSE & NCTS Special Seminar] ​Hamiltonian Phase Error in Resonantly Driven CNOT Gate Above the Fault-Tolerant Threshold
Speaker: Mr. Yi-Hsien Wu (NTU & RIKEN)
Time: 2023/08/22 (Tue.) 14:30-15:30
Place: NCTS Physics Lecture Hall, 4F, Chee-Chun Leung Cosmology Hall, NTU
Online: https://nationaltaiwanuniversity-zbh.my.webex.com/nationaltaiwanuniversity-zbh.my/j.php?MTID=md21f554abf32352d0c95b8ae66b03572

Electron spin qubits are a promising platform for scalable quantum processors due to their
long coherence time and the compatibility with semiconductor industrial processes. To achieve
a large scale quantum processor, quantum error correction needs to be implemented and this
requires the quantum gate fidelities of the processor to be above a certain fault-tolerant
threshold. By obtaining a detailed understanding of our quantum gates we can use this
knowledge to improve the gate fidelity. In this work we demonstrate a simple yet reliable
calibration procedure for a high-fidelity controlled-rotation gate in an exchange-always-on
Silicon quantum processor, allowing operation above the fault-tolerance threshold of quantum
error correction. We find that the fidelity of our uncalibrated controlled-rotation gate is limited
by coherent errors in the form of controlled-phases due to an off-resonant driving. We present
a method to measure and compensate for the effect of these phase errors to improve our gate
fidelity. We then evaluate the improved gate fidelities by randomized benchmark and gate-set
tomography protocols. The experimental results are compared with gate-set-tomography
results with simulated data. The simulated data matches well with the experimental one,
indicating the error measured in experiment is the error we assumed in our simulation. Finally,
we use our phase compensation protocol to implement a virtual, high-fidelity controlled-phase

Reference: Wu, Y. H. et al., arXiv:2307.09031v1 [cond-mat.mes-hall]

Yi-Hsien Wu received his bachelor’s degree from Department of Physics, National Central
University. He is now a PhD. Student at the Department of Physics, National Taiwan University
under supervision of Prof. Hsi-Sheng Goan, and is also studying as an International Program
Associate at the Quantum Functional System Research Group, RIKEN, Japan. His research
interests include quantum dot experiments and Silicon spin qubits.