Universal quantum gate with hybrid qubits in circuit quantum electrodynamics

TL;DR

This paper proposes a simple, high-fidelity universal controlled-phase gate for hybrid qubits in circuit QED, utilizing a superconducting flux qutrit and two 3D microwave cavities, with potential for broad physical implementation.

Contribution

It introduces a novel method for implementing a universal controlled-phase gate between hybrid qubits using a single operation without classical pulses or measurements.

Findings

High fidelity gate achievable with current technology

Gate operates with the qutrit remaining in the ground state

Applicable to various physical systems with cavities and three-level atoms

Abstract

Hybrid qubits have recently drawn intensive attention in quantum computing. We here propose a method to implement a universal controlled-phase gate of two hybrid qubits via two three-dimensional (3D) microwave cavities coupled to a superconducting flux qutrit. For the gate considered here, the control qubit is a microwave photonic qubit (particle-like qubit), whose two logic states are encoded by the vacuum state and the single-photon state of a cavity, while the target qubit is a cat-state qubit (wave-like qubit), whose two logic states are encoded by the two orthogonal cat states of the other cavity. During the gate operation, the qutrit remains in the ground state; therefore decoherence from the qutrit is greatly suppressed. The gate realization is quite simple, because only a single basic operation is employed and neither classical pulse nor measurement is used. Our numerical simulations demonstrate that with current circuit QED technology, this gate can be realized with a high fidelity. The generality of this proposal allows to implement the proposed gate in a wide range of physical systems, such as two 1D or 3D microwave or optical cavities coupled to a natural or artificial three-level atom. Finally, this proposal can be applied to create a novel entangled state between a particle-like photonic qubit and a wave-like cat-state qubit.