High-Fidelity Controlled-Phase Gate for Binomial Codes via Geometric Phase Engineering

TL;DR

This paper introduces a geometric phase engineering method to implement high-fidelity controlled-phase gates for binomially encoded logical qubits, achieving a process fidelity of 97.4% and surpassing previous results.

Contribution

It presents a novel geometric phase engineering approach that simplifies control and incorporates system nonlinearities for fast, high-fidelity bosonic logical gates.

Findings

Achieved a 97.4% process fidelity for a controlled-Z gate.

Demonstrated the method's superiority over previous bosonic gate fidelities.

Validated the approach experimentally with high fidelity.

Abstract

High-fidelity two-logical-qubit gates are essential for realizing fault-tolerant quantum computation with bosonic codes, yet experimentally reported fidelities have rarely exceeded 90\%. Here, we propose a geometric phase engineering approach for implementing controlled-phase gates for binomially encoded logical qubits. This method leverages the structural simplicity of geometric drives to reduce the numerical optimization dimensionality while fully incorporating system nonlinearities, enabling fast and high-fidelity logical operations. As an example, we experimentally demonstrate a process fidelity of 97.4$\pm$0.8\% for a controlled-Z gate between two binomial codes, surpassing all previously reported two-logical-qubit gates in bosonic codes. This work demonstrates that geometric phase engineering provides an effective and experimentally feasible route to fast, high-fidelity logical operations in bosonic quantum processors.