Experimental investigation of a four-qubit linear-optical quantum logic circuit

Area of Science:

• Quantum Information Science
• Quantum Computing
• Linear Optics Quantum Computing

Background:

• Quantum logic circuits are fundamental for quantum computation.
• Implementing multi-qubit gates and entanglement is crucial for scalable quantum systems.

Purpose of the Study:

• To experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit.
• To implement and verify a genuine four-qubit controlled-controlled-controlled-Z (C(3)Z) gate.

Main Methods:

• Encoding two qubits into polarization and path degrees of freedom of single photons.
• Utilizing two crossed, inherently stable interferometers.
• Employing Hofmann bounds and Monte Carlo sampling for fidelity verification.

Main Results:

• Successfully demonstrated a robust four-qubit linear-optical quantum logic circuit.
• Verified high-fidelity performance of the C(3)Z gate.
• Experimentally generated and certified genuine multipartite entanglement.

Conclusions:

• The developed scheme is versatile for complex quantum logic operations.
• This work advances the development of scalable photonic quantum computers.
• The circuit's ability to generate entanglement is a key step towards quantum networking.