Fast parametric two-qubit gate for highly detuned fixed-frequency superconducting qubits using a double-transmon coupler

TL;DR

This paper demonstrates a fast, high-fidelity two-qubit gate for highly detuned fixed-frequency superconducting qubits using a double-transmon coupler, enabling efficient quantum operations with minimal crosstalk.

Contribution

The study introduces a novel application of the double-transmon coupler for high-fidelity, fast entangling gates on highly detuned fixed-frequency qubits, overcoming previous limitations.

Findings

Achieved a $ oot i ext{SWAP}$ gate with over 99.99% fidelity in 24 ns.

Realized a CZ gate with over 99.99% fidelity in 18 ns.

Demonstrated the feasibility of high-performance gates for highly detuned qubits using DTC.

Abstract

High-performance two-qubit gates have been reported with superconducting qubits coupled via a single-transmon coupler (STC). Most of them are implemented for qubits with a small detuning since reducing residual $ZZ$ coupling for highly detuned qubits by an STC is challenging. In terms of the frequency crowding and crosstalk, however, highly detuned qubits are desirable. Here, we numerically demonstrate a high-performance parametric gate for highly detuned fixed-frequency qubits using a recently proposed tunable coupler called a double-transmon coupler (DTC). Applying an ac flux pulse, we can perform a maximally entangling universal gate ($\sqrt{\rm iSWAP}$) with an average fidelity over 99.99$\%$ and a short gate time of about 24 ns. This speed is comparable to resonance-based gates for slightly detuned tunable qubits. Moreover, using a dc flux pulse alternatively, we can achieve another kind of entangling gate called a CZ gate with an average fidelity over 99.99$\%$ and a gate time of about 18 ns. Given the frexibility and feasible settings, we can expect that the DTC will contribute to realizing a high-performance quantum computer in the near future.