Native two-qubit gates in fixed-coupling, fixed-frequency transmons beyond cross-resonance interaction

TL;DR

This paper demonstrates the implementation of native two-qubit gates beyond the traditional cross-resonance interaction in fixed-frequency transmon qubits, enhancing quantum gate versatility and efficiency.

Contribution

It introduces and benchmarks native ISWAP, SWAP, and BSWAP gates using microwave drives, surpassing cross-resonance gates in performance and enabling efficient construction of complex entangling gates.

Findings

Native two-qubit gates outperform cross-resonance-based gates.

Efficient construction of the B-gate as a perfect entangler.

Resonance conditions and a novel frame tracking technique are developed.

Abstract

Fixed-frequency superconducting qubits demonstrate remarkable success as platforms for stable and scalable quantum computing. Cross-resonance gates have been the workhorse of fixed-coupling, fixed-frequency superconducting processors, leveraging the entanglement generated by driving one qubit resonantly with a neighbor's frequency to achieve high-fidelity, universal CNOTs. Here, we use on-resonant and off-resonant microwave drives to go beyond cross-resonance, realizing natively interesting two-qubit gates that are not equivalent to CNOTs. In particular, we implement and benchmark native ISWAP, SWAP, $\sqrt{\text{ISWAP}}$, and BSWAP gates. Furthermore, we apply these techniques for an efficient construction of the B-gate: a perfect entangler from which any two-qubit gate can be reached in only two applications. We show these native two-qubit gates are better than their counterparts compiled from cross-resonance gates. We elucidate the resonance conditions required to drive each two-qubit gate and provide a novel frame tracking technique to implement them in Qiskit.