Coupling silicon qubits via a high-impedance superconducting resonator

Spin qubits in semiconductors like silicon are widely perceived as an ideal technology platform to realize a quantum computer. Their advantages range from the high integration density and the mature manufacturing technology of classical computers, to their long lifetimes and low error rates. On the other hand, spins in semiconductors are not easy to couple over long distances. For this, optical or microwave photons are much better suited. Here, I will describe our experimental efforts to couple two spin qubits 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. The high impedance and kinetic inductance come with microwave engineering challenges (e.g. leakage through the gate fanout) and we discuss several approaches to overcome these. Finally, we demonstrate operation of a device with two silicon double quantum dots coupled to the same resonator. 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 charge sensors.