Implementation of pairwise longitudinal coupling in a three-qubit superconducting circuit

TL;DR

This paper introduces the 'trimon', a superconducting circuit with three qubits that are all-to-all longitudinally coupled, enabling efficient quantum operations and enhanced qubit protection, advancing multi-qubit quantum computing architectures.

Contribution

The paper presents a novel three-qubit superconducting circuit with all-to-all longitudinal coupling and qubit protection, facilitating universal quantum gates and improved qubit coherence.

Findings

High-fidelity state swapping demonstrated

All three qubits coupled to a transmon characterized

Two qubits protected against Purcell decay

Abstract

We present the "trimon", a multi-mode superconducting circuit implementing three qubits with all-to-all longitudinal coupling. This always-on interaction enables simple implementation of generalized controlled-NOT gates which form a universal set. Further, two of the three qubits are protected against Purcell decay while retaining measurability. We demonstrate high-fidelity state swapping operations between two qubits and characterize the coupling of all three qubits to a neighbouring transmon qubit. Our results offer a new paradigm for multi-qubit architecture with applications in quantum error correction, quantum simulations and quantum annealing.