A universal gate for fixed-frequency qubits via a tunable bus

TL;DR

This paper presents a tunable bus method that enables high-fidelity coupling of fixed-frequency superconducting qubits separated by large detunings, facilitating scalable quantum computing and simulation.

Contribution

Introduction of a tunable bus technique that couples fixed-frequency qubits at large detunings via parametric oscillation, enabling efficient two-qubit gates.

Findings

Achieved a 183ns iSWAP gate with 98.23% fidelity.

Enabled coupling of qubits separated by 854MHz.

Demonstrated potential for scalable quantum circuits.

Abstract

A challenge for constructing large circuits of superconducting qubits is to balance addressability, coherence and coupling strength. High coherence can be attained by building circuits from fixed-frequency qubits, however, leading techniques cannot couple qubits that are far detuned. Here we introduce a method based on a tunable bus which allows for the coupling of two fixed-frequency qubits even at large detunings. By parametrically oscillating the bus at the qubit-qubit detuning we enable a resonant exchange (XX+YY) interaction. We use this interaction to implement a 183ns two-qubit iSWAP gate between qubits separated in frequency by 854MHz with a measured average fidelity of 0.9823(4) from interleaved randomized benchmarking. This gate may be an enabling technology for surface code circuits and for analog quantum simulation.