New Design of three-qubit system with three transmons and a single fixed-frequency resonator coupler

TL;DR

This paper proposes a new three-qubit transmon system with a single fixed-frequency resonator coupler, achieving high-fidelity CNOT gates and potentially enabling more connected and scalable superconducting quantum computers.

Contribution

The paper introduces a novel three-transmon system with a single resonator coupler that improves qubit connectivity while maintaining high gate fidelity.

Findings

CNOT gate fidelity exceeds 0.98 in the proposed structure

The structure allows increased qubit connections without compromising performance

Potential for scalable, high-connectivity transmon-based quantum computers

Abstract

The transmon, which has a short gate time and remarkable scalability, is the most commonly utilized superconducting qubit, based on the Cooper pair box as a qubit or coupler in superconducting quantum computers. Lattice and heavy-hexagon structures are well-known large-scale configurations for transmon-based quantum computers that classical computers cannot simulate. These structures share a common feature: a resonator coupler that connects two transmon qubits. Although significant progress has been made in implementing quantum error correction and quantum computing using quantum error mitigation, fault-tolerant quantum computing remains unachieved due to the inherent vulnerability of these structures. This raises the question of whether the transmon-resonator-transmon structure is the best option for constructing a transmon-based quantum computer. To address this, we demonstrate that the average fidelity of CNOT gates can exceed 0.98 in a structure where a resonator coupler mediates the coupling of three transmon qubits. This result suggests that our novel structure could be a key method for increasing the number of connections among qubits while preserving gate performance in a transmon-based quantum computer.