Kavli Affiliate: Giordano Scappucci
| First 5 Authors: Florian K. Unseld, Brennan Undseth, Eline Raymenants, Yuta Matsumoto, Saurabh Karwal
| Summary:
Micromagnet-enabled electric-dipole spin resonance (EDSR) is an established
method of high-fidelity single-spin control in silicon. However, the resulting
architectural limitations have restrained silicon quantum processors to
one-dimensional arrays, and heating effects from the associated microwave
dissipation exacerbates crosstalk during multi-qubit operations. In contrast,
qubit control based on hopping spins has recently emerged as a compelling
primitive for high-fidelity baseband control in sparse two-dimensional hole
arrays in germanium. In this work, we commission a $^{28}$Si/SiGe 2×2 quantum
dot array both as a four-qubit device with pairwise exchange interactions using
established EDSR techniques and as a two-qubit device using baseband hopping
control. In this manner, we can evaluate the two modes of operation in terms of
fidelity, coherence, and crosstalk. We establish a lower bound on the fidelity
of the hopping gate of 99.50(6)%, which is similar to the average fidelity of
the resonant gate of 99.54(4)%. Lowering the external field to reach the
hopping regime nearly doubles the measured $T_2^{mathrm{H}}$, suggesting a
reduced coupling to charge noise. Finally, the hopping gate circumvents the
transient pulse-induced resonance shift. To further motivate the hopping gate
approach as an attractive means of scaling silicon spin-qubit arrays, we
propose an extensible nanomagnet design that enables engineered baseband
control of large spin arrays.
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