A two-qubit entangling gate based on a two-spin gadget

TL;DR

This paper proposes a fast, high-fidelity two-qubit entangling gate for flux qubits using a two-spin gadget, enabling efficient quantum operations suitable for large-scale quantum computing.

Contribution

It introduces a novel two-spin gadget-based CNOT-equivalent gate with over 99.9% fidelity in 40ns, and translates spin model parameters to circuit flux bias schedules for practical implementation.

Findings

Achieves >99.9% fidelity within 40ns

Suitable for large-scale flux qubit systems with inductive couplings

Resolves speed-coherence conflict in quantum gate design

Abstract

The faster speed and operational convenience of two-qubit gate with flux bias control makes it an important candidate for future large-scale quantum computers based on high coherence flux qubits. Based on a properly designed two-spin gadget which has small gaps during the evolution of energy levels, we build a CNOT-equivalent gate which can reach a fidelity larger than 99.9% within 40ns. Moreover, we also use the Schrieffer-Wolff Transformation to translate the spin model Ising coefficients schedule to circuit model flux bias schedule for realistic flux qubit circuits coupled by a tunable rf-squid. The two-qubit entangling gate scheme introduced here is suitable for realizing efficient two-qubit gates in the large scale flux qubit systems dominated by inductive couplings. Comparing with the current gate-based quantum computation systems dominated by capacitive couplings, it can resolve the conflict between the speed and a high coherence.