Universal quantum gate with hybrid qubits in circuit quantum electrodynamics.

Area of Science:

• Quantum Computing
• Quantum Information Science
• Superconducting Circuits

Background:

• Hybrid qubits are crucial for advancing quantum computing.
• Implementing controlled quantum gates is essential for building quantum computers.
• Superconducting circuits offer a promising platform for quantum information processing.

Purpose of the Study:

• To propose a novel method for implementing a universal controlled-phase gate between two hybrid qubits.
• To utilize microwave cavities and a superconducting flux qutrit for gate implementation.
• To explore the potential for high-fidelity quantum operations in a simplified gate scheme.

Main Methods:

• Utilizing two 3D microwave cavities coupled to a superconducting flux qutrit.
• Encoding control qubit states in cavity photon numbers (vacuum and single-photon states).
• Encoding target qubit states in orthogonal cat states within another cavity.

Main Results:

• Demonstrated a method for a universal controlled-phase gate with suppressed qutrit decoherence by keeping it in the ground state.
• Numerical simulations indicate high fidelity achievable with current circuit quantum electrodynamics technology.
• The proposed gate requires only a single basic operation, without classical pulses or measurement.

Conclusions:

• The proposed method offers a simple and high-fidelity approach to implementing a controlled-phase gate for hybrid qubits.
• The generality of the proposal allows for its application in various physical systems, including optical cavities coupled to three-level atoms.
• This work paves the way for creating novel entangled states between particle-like photonic and wave-like cat qubits.