High-fidelity qutrit entangling gates for superconducting circuits

Area of Science:

• Quantum Information Science
• Superconducting Circuits
• Quantum Computing

Background:

• Ternary quantum information processing (using qutrits) offers advantages over binary systems (qubits).
• Transmon devices, commonly used as qubits, possess accessible higher energy levels suitable for qutrit operation.
• High-fidelity single qutrit operations have been achieved, but two-qutrit entanglement remains a challenge.

Purpose of the Study:

• To engineer high-fidelity two-qutrit entanglement in fixed-frequency transmon devices.
• To develop a flexible, microwave-activated method for dynamic entanglement.
• To demonstrate the creation of essential quantum gates for ternary processing.

Main Methods:

• Utilized the differential AC Stark shift to induce cross-Kerr entanglement between two transmon qutrits.
• Employed microwave activation for dynamic control of the entanglement.
• Extended existing ZZ interaction techniques from transmon qubits to qutrits.

Main Results:

• Achieved flexible, microwave-activated, dynamic cross-Kerr entanglement between two transmon qutrits.
• Engineered high-fidelity qutrit CZ† and CZ gates with estimated process fidelities of 97.3(1)% and 95.2(3)%, respectively.
• Demonstrated a significant advancement in multi-transmon qutrit operation.

Conclusions:

• The differential AC Stark shift is an effective method for high-fidelity two-qutrit entanglement in transmon devices.
• This work overcomes a key challenge in realizing scalable ternary quantum information processing.
• The demonstrated qutrit gates pave the way for more complex ternary quantum computations and simulations.