Toward Long-coherence-time Si Spin Qubit: The Origin of Low-frequency Noise in Cryo-CMOS

We have experimentally clarified the origin of low-frequency noise, which limits the coherence-time in Si quantum bit (qubit), utilizing cryo-CMOS. At cryogenic temperature (2.5 K), significantly enhanced $1/f$ noise is observed in Si MOSFETs, while it is not seen at room temperature. Interface trap density dependence of noise in Si MOSFETs, changing the surface orientation, revealed that the cryogenic $1/f$ noise is governed by carrier number fluctuation and we identified that the origin of the $1/f\mathrm{noise}$ is interface trap at cryogenic temperature, for the first time. The present study demonstrates that the experiments using well-investigated MOSFETs can provide new knowledge on Si qubits, which it is hardly possible to investigate using Si qubit as itself.