Quantum circuit mapping for universal and scalable computing in MZI-based integrated photonics

Area of Science:

• Quantum Information Science
• Integrated Photonics
• Quantum Computing

Background:

• Linear optical quantum computing (LOQC) leverages robust technology and flexible conditions, aligning with DiVincenzo's criteria.
• Integrated photonics enables gate-based quantum computing using path-encoded qubits and Mach-Zehnder interferometers (MZIs).
• Post-selected controlled-Z (CZ) gates are resource-efficient for universal two-qubit operations but lack regular structure and cascadability, hindering scalability.

Purpose of the Study:

• To develop a universal and scalable LOQC approach on integrated photonic platforms.
• To overcome limitations of existing post-selected CZ gates for large-scale quantum computation.
• To demonstrate the feasibility of generating entangled states using the proposed scalable architecture.

Main Methods:

• Extended path-encoded dual-rail qubits to a triplet of waveguides, including an auxiliary waveguide.
• Introduced a swap photonic network to map qubit structures for the post-selected CZ gate.
• Developed an optical swap gate for non-nearest neighbor qubit interactions and demonstrated cascading of CZ gates.

Main Results:

• A novel, regularly structured path-encoded qubit suitable for scalable integrated photonics.
• Demonstrated deterministic qubit location exchange and controlled quantum gates between arbitrary path-encoded qubits.
• Successfully implemented cascading of post-selected CZ gates by truncating auxiliary waveguides.
• Showcased Bell and Greenberger-Horne-Zeilinger (GHZ) state generation circuits utilizing the regular structure, cascading, and optical swap.

Conclusions:

• The proposed approach enables universal and scalable LOQC on integrated photonic platforms.
• The developed methods overcome the structural and cascading limitations of previous LOQC implementations.
• This work paves the way for building larger and more complex photonic quantum computers.