Characterizing d-dimensional quantum channels by means of quantum process tomography

Area of Science:

• Quantum Information Science
• Optical Physics
• Quantum Computing

Background:

• Characterizing quantum systems is crucial for quantum computing and information processing.
• Higher-dimensional Hilbert spaces (d>2) offer enhanced computational power but pose significant characterization challenges.
• Existing methods for quantum process tomography can be complex and resource-intensive.

Purpose of the Study:

• To propose and demonstrate a simple optical architecture for characterizing general quantum processes in photonic spatial quantum systems.
• To reconstruct various noise channels and simulated atmospheric turbulence in higher-dimensional Hilbert spaces.
• To validate the proposed architecture using quantum process tomography and state fidelity measurements.

Main Methods:

• Utilizing phase-only programmable spatial light modulators for optical architecture.
• Implementing quantum process tomography to reconstruct the quantum channel matrix (χ).
• Experimentally measuring state fidelities before and after the quantum channel.

Main Results:

• Successfully reconstructed amplitude shifts, phase shifts, and depolarizing channels in a 5-dimensional (d=5) Hilbert space.
• Reconstructed simulated atmospheric turbulence effects on qudits in a 4-dimensional (d=4) free-space transmission.
• Achieved experimental state fidelities exceeding 97% after the quantum channel.

Conclusions:

• The proposed simple optical architecture effectively characterizes general quantum processes in higher-dimensional photonic systems.
• This method provides a robust tool for understanding and mitigating noise in quantum computing and communication.
• The demonstrated high fidelities highlight the practical applicability of the technique for quantum information science.