Proposal of multi-mode couplers for all-to-all connectivity and long-distance couplings for superconducting qubits

Common designs of superconducting QPU only support local two-qubit gates. Multi-qubit operations and long distance gates have to be complied into a series of local one-qubit and two-qubit gates. The low connectivity in superconducting systems has become a crucial bottleneck for scaling up superconducting QPU and implementing error correction. Building on our previous theory of multi-mode couplers, we propose a coupler and QPU design with superconducting qubits that support native all-to-all connectivity and long distance couplings. In our design, each module consists of a central multi-mode coupler with qubits around it. The central coupler provides all-to-all coupling within the module. Between the modules, central couplers are coupled via a bus coupler. The central couplers and the bus coupler together provide long-distance coupling among qubits in different modules. We give theory analysis and numerical simulations for such a QPU design. We believe this gives a feasible path for scaling up superconducting qubits.