Tunable coupler for realizing a controlled-phase gate with dynamically decoupled regime in a superconducting circuit

TL;DR

This paper demonstrates a flux-controlled tunable coupler for superconducting qubits that enables high-fidelity controlled-phase gates with dynamic decoupling, improving scalability and reducing unwanted interactions.

Contribution

It introduces a simple, flux-controlled tunable coupler with continuous adjustment, enabling a dynamically decoupled CZ gate with high fidelity in superconducting circuits.

Findings

Achieved 98.3% average CZ gate fidelity.

Demonstrated suppression of qubit-qubit coupling during tuning.

Enabled geometric two-qubit phase at the operating point.

Abstract

Controllable interaction between superconducting qubits is desirable for large-scale quantum computation and simulation. Here, based on a theoretical proposal by Yan et al. [Phys. Rev. Appl. 10, 054061 (2018)] we experimentally demonstrate a simply-designed and flux-controlled tunable coupler with a continuous tunability by adjusting the coupler frequency, which can completely turn off adjacent superconducting qubit coupling. Utilizing the tunable interaction between two qubits via the coupler, we implement a different type of controlled-phase (CZ) gate with 'dynamically decoupled regime', which allows the qubit-qubit coupling to be only 'on' at the usual operating point while dynamically 'off' during the tuning process of one qubit frequency into and out of the operating point. This scheme not only efficiently suppresses the leakage out of the computational subspace, but also allows for the acquired two-qubit phase being geometric at the operating point. We achieve an average CZ gate fidelity of 98.3(0.6), which is dominantly limited by qubit decoherence. The demonstrated tunable coupler provides a desirable tool to suppress adjacent qubit coupling and is suitable for large scale quantum computation and simulation.