Two-qubit logic between distant spins in silicon*

Semiconductor spin qubits hold promise for quantum computation due to their long coherence times and potential for scaling. So far, interactions between spin qubits are limited to spins a few hundreds of nanometers apart. A distributed architecture with local registers and long-range couplers will be needed to scale up to millions of qubits. Circuit quantum electrodynamics can provide a pathway to realize interactions between distant spins. Here, we report long-range two-qubit logic using an on-chip superconducting resonator.

We first show universal single-qubit control over two distant spin qubits separated by 250 µm and characterize their coherence times. Next, we couple the two spins via virtual photons in a superconducting resonator, and show two-qubit iSWAP logic between the distant qubits with an interaction strength of 21 MHz. This frequency is consistent with spectroscopic measurements. Furthermore, we demonstrate that the coupling strength as well as the coherence times of the qubits can be tuned by the inter-dot tunnel coupling and the spin-cavity detuning. In future work we intend to implement single-shot readout and improve the spin lifetimes while dispersively coupled to the resonator. These results pave the way for scalable networks of spin qubits on a chip.