Coupling silicon spin qubits via a high-impedance superconducting resonator

Spin qubits in silicon quantum dots are widely perceived as an ideal technology platform to realize a quantum computer. However, spins in semiconductors are not easy to couple over long distances. In this work, I will describe our experimental efforts to couple two spin qubits in Si/SiGe through a superconducting microwave resonator. To enlarge the coupling to the qubit charge dipole, we use a high-kinetic-inductance NbTiN nanowire resonator and achieve a large impedance of about 3 kΩ, resulting in a charge-resonator coupling strength g_c/2π of 220 MHz and a resonator linewidth of about 2 MHz. I will demonstrate the operation of a device with two single spins, separated by 250 µm, that are resonantly coupled to the resonator simultaneously, with single-spin coupling strengths g_s/2π in excess of 12 MHz. Our work opens up opportunities to adapt very powerful and well-developed techniques from circuit quantum electrodynamics and superconducting qubits to the spin qubit world. These opportunities include long-range coupling of spin qubits, and fast spin readout without local charge sensor structures.