Nonlinear response and crosstalk of strongly driven spin qubits*

Spin qubits in gate-defined quantum dots in silicon are one of the most promising platforms for large-scale quantum computers. To implement deep-circuit quantum algorithms such as quantum error correction, long coherence times and fast operations are needed. In electric dipole spin resonance (EDSR), where electric signals are converted to magnetic signals, the anharmonicity of confinement potential becomes crucial in strong driving regime [1]. Utilizing two spin qubits in a Si/SiGe heterostructure, we have found a crosstalk effect which behaves as an amplitude modulation and a frequency modulation in the Rabi oscillation experiments. This effect is observed routinely but not well understood [2, 3]. Supported by a theoretical model, we provide evidence that the crosstalk is induced by the nonlinear confinement when both qubits are being strongly driven simultaneously. Furthermore, we study the impact of crosstalk on the control fidelities andcrosstalk mitigation by Hamiltonian engineering.
[1] P. Scarlino, et al. PRL, 115, 106802 (2015).
[2] T. F. Watson, et al. Nature, 555, 633–637 (2018).
[3] K. Takeda, et al. npj Quantum Information 4(1), 1-6 (2018).