Microwave-activated two-qubit gates for fixed-coupling and fixed-frequency transmon qubits

TL;DR

This paper presents a microwave-activated controlled-Z gate scheme for fixed-frequency transmon qubits, achieving high fidelity and suppressing leakage, which simplifies control and aids scalability in superconducting quantum computing.

Contribution

It introduces a microwave-only control protocol for fixed-frequency transmons that enhances fidelity and reduces complexity compared to traditional tunable approaches.

Findings

Gate fidelity exceeds 0.999 within 150 ns

Leakage to non-computational states is effectively suppressed

The protocol simplifies control in fixed-frequency superconducting qubits

Abstract

All-microwave control of fixed-frequency superconducting quantum systems offers the potential to reduce control circuit complexity and increase system coherence. Nevertheless, due to the limited control flexibility in qubit parameters, one has to address several issues, such as quantum crosstalk and frequency crowding, for scaling up qubit architecture with non-tunable elements. This study proposes a microwave-activated two-qubit gate scheme for two fixed-frequency transmon qubits coupled via a fixed-frequency transmon coupler. The protocol relies on applying a microwave pulse exclusively to the coupler, enabling the implementation of a controlled-Z (CZ) gate. We show that the gate fidelity exceeding 0.999 can be achieved within 150 ns, excluding decoherence effects. Moreover, we also show that leakage from the computational subspace to non-computational states can also be effectively suppressed.