Multi-mode superconducting circuits for realizing strongly coupled multi-qubit processor units

TL;DR

This paper introduces multi-mode superconducting circuits with all-to-all longitudinal coupling, enabling efficient manipulation of multi-qubit systems for scalable quantum computing.

Contribution

It proposes a novel class of superconducting circuits that realize all-to-all longitudinal coupling among multiple transmon qubits, enhancing quantum processor scalability.

Findings

Circuits enable direct implementation of multi-dimensional Hilbert spaces.

Always-on longitudinal coupling simplifies qubit manipulation.

Design optimization for small-scale quantum processors.

Abstract

Inter-qubit coupling and qubit connectivity in a processor are crucial for achieving high fidelity multi-qubit gates and efficient implementation of quantum algorithms. Typical superconducting processors employ relatively weak transverse inter-qubit coupling which are activated via frequency tuning or microwave drives. Here, we propose a class of multi-mode superconducting circuits which realize multiple transmon qubits with all-to-all longitudinal coupling. These "artificial molecules" directly implement a multi-dimensional Hilbert space that can be easily manipulated due to the always-on longitudinal coupling. We describe the basic technique to analyze such circuits, compute the relevant properties and discuss how to optimize them to create efficient small-scale quantum processors with universal programmability.