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arXiv · 1909.11397

Low-frequency spin qubit detuning noise in highly purified $^{28}$Si/SiGe

Tom Struck·Arne Hollmann·Floyd Schauer·Olexiy Fedorets·Andreas Schmidbauer·Kentarou Sawano·Helge Riemann·Nikolay V. Abrosimov·Łukasz Cywiński·Dominique Bougeard·Lars R. Schreiber
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Abstract

The manipulation fidelity of a single electron qubit gate-confined in a $^{28}$Si/SiGe quantum dot has recently been drastically improved by nuclear isotope purification. Here, we identify the dominant source for low-frequency qubit detuning noise in a device with an embedded nanomagnet, a remaining $^{29}$Si concentration of only 60$\,$ppm in the strained $^{28}$Si quantum well layer and a spin echo decay time $T_2^{\text{echo}}=128\,\mu$s. The power spectral density (PSD) of the charge noise explains both the observed transition of a $1/f^2$- to a $1/f$-dependence of the detuning noise PSD as well as the observation of a decreasing time-ensemble spin dephasing time from $T_2^* \approx 20\,\mu$s with increasing measurement time over several hours. Despite their strong hyperfine contact interaction, the few $^{73}$Ge nuclei overlapping with the quantum dot in the barrier do not limit $T_2^*$, as their dynamics is frozen on a few hours measurement scale. We conclude that charge noise and the design of the gradient magnetic field is the key to further improve the qubit fidelity.

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Tom Struck, Arne Hollmann, Floyd Schauer, Olexiy Fedorets, Andreas Schmidbauer, Kentarou Sawano, Helge Riemann, Nikolay V. Abrosimov, Łukasz Cywiński, Dominique Bougeard, Lars R. Schreiber. 2019-09-25. Low-frequency spin qubit detuning noise in highly purified $^{28}$Si/SiGe. https://doi.org/10.1038/s41534-020-0276-2

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