Fast quantum measurement of a hopping Ge-hole spin qubit via dynamical longitudinal coupling to a superconducting resonator

We consider a possibility for a fast quantum readout of a Ge-hole quantum dot (QD) spin qubit based on recently proposed semiconductor hopping spins [1]. The single-QD spin state is mapped to an intermediary singlet-triplet qubit whose state is measured via the dynamical longitudinal coupling in a dispersive regime [2]. While using similar on-chip superconducting resonator for the measurement (compare to Ref. [3]) the corresponding quantum measurement rate can be made much faster, by one-two orders of magnitude, than the usual dispersive rate, allowing to overcome typical dephasing mechanisms such as a charge noise, phonon relaxation, and coupling to TLS fluctuators. We further discuss readout optimization at various quantum dots’ detunings bearing in mind the strong spin-orbit effects.

[1] Chien-An Wang et al., Operating semiconductor quantum processors with hopping spins, Science 385, 447-452 (2024)

[2] R. Ruskov, C. Tahan, Longitudinal (curvature) couplings of an N-level qudit to a superconducting resonator at the adiabatic limit and beyond, Phys. Rev. B 109, 245303 (2024)

[3] Guoji Zheng et al., Rapid gate-based spin readout in silicon using an on-chip resonator, Nature Nanotechnology 14, 742-746 (2019)