Ellipsometry with polarisation-entangled photons

Area of Science:

• Quantum optics
• Solid-state physics
• Materials science

Background:

• Ellipsometry is a standard technique for measuring optical properties of thin films and surfaces.
• Traditional ellipsometry can be limited by systematic errors and sample properties.
• Quantum entanglement offers potential for enhanced precision in optical measurements.

Purpose of the Study:

• To develop and demonstrate a novel quantum-enhanced ellipsometry technique.
• To accurately measure ellipsometric angles of silicon dioxide films and BK7 glass.
• To validate the quantum approach by comparing results with expected values.

Main Methods:

• Utilized polarization-entangled photon pairs from a two-crystal, type-I spontaneous parametric down-conversion source.
• Developed a quantum tomography technique to estimate the density matrix of entangled photons before and after sample interaction.
• Calculated ellipsometric angles from the reconstructed density matrix components.

Main Results:

• Successfully measured ellipsometric angles for a silicon dioxide film on silicon.
• Accurately determined internal and external reflection properties of BK7 glass.
• Experimental measurements showed good agreement with expected optical values.

Conclusions:

• Polarization-entangled photons combined with quantum tomography provide a powerful tool for precise ellipsometric measurements.
• This quantum approach offers a viable alternative to conventional ellipsometry, especially for challenging samples.
• The technique demonstrates the practical application of quantum phenomena in optical metrology.