Longitudinal coupling to hole spin qubits demonstrated in a silicon fin field-effect transistor

Quantum computers promise exponential speed-up for certain problems. Silicon quantum dot holes spin qubits are prime candidates for scalable quantum computing owing to their small footprint and compatibility with current semiconductor foundry fabrication techniques. The devices used here are silicon fin field-effect transistors (FinFETs) [1] which allow for spin qubit operation above 4K [2].



In this work, we investigate the longitudinal coupling of spin qubits to a MW electric field, i.e. an interaction of the form $propto sigma_z V_{MW} cos(omega t)$. This type of interaction has been proposed for efficient spin-resonator coupling for spin readout or long-range two-qubit gates [3,4], due to its many advantages, such as no resonator back-action or temperature resilience. However, since a longitudinally coupled MW field does not induce Rabi oscillations, it is not straightforward to extract the coupling strength. Here, we use a new technique: in a multi-tone experiment the longitudinal coupling renormalizes the Rabi oscillations induced by a transversally coupled electric field. Surprisingly, this effect becomes stronger when detuning the longitudinal driving field from the qubit Larmor frequency. Using the right parameters, the Rabi oscillations originating from the transversal drive can be switched off by the longitudinal driving field. In this condition we can quantify the coupling strength of the spin qubit to a longitudinal field and observe higher harmonics of the Rabi oscillations.



[1] Geyer et al., Appl. Phys. Lett. 118, 104004 (2021)

[2] Camenzind et al., Nat Electron 5, 178 (2022)

[3] Bosco et al., Phys. Rev. Lett. 129, 066801 (2022)

[4] Bøttcher et al., Nat Commun 13, 4773 (2022)