Spectral correlation and interference in continuous-wave non-degenerate photon pairs at telecom wavelengths

Area of Science:

• Quantum Optics
• Nonlinear Optics
• Materials Science

Background:

• Entangled photon pairs are fundamental resources for quantum information processing and quantum communication.
• Periodically poled lithium niobate (PPLN) is a key material for nonlinear optical applications, including spontaneous parametric down-conversion (SPDC).
• Achieving high-quality entangled photon sources requires precise control over the down-conversion process and photon properties.

Purpose of the Study:

• To develop and characterize a novel entangled photon pair source utilizing a domain-engineered type-II PPLN crystal.
• To investigate the spectral correlations of the generated entangled photons.
• To assess the indistinguishability of the down-converted photons for high entanglement visibility.

Main Methods:

• Fabrication of a domain-engineered, type-II PPLN crystal.
• Generation of entangled photon pairs via SPDC at telecom wavelengths (1533 nm and 1567 nm).
• Characterization of spectral correlations using fiber-assisted signal-photon spectroscopy.
• Observation of Hong-Ou-Mandel interference after erasing polarization distinguishability.

Main Results:

• Successful generation of entangled photon pairs at 1533 nm and 1567 nm from the custom PPLN crystal.
• Demonstrated spectral correlations between the signal and idler photons.
• Observed clear Hong-Ou-Mandel interference, indicating high indistinguishability between the down-conversion paths.
• The interference signature directly correlates with spectral correlations, a key parameter for entanglement fidelity.

Conclusions:

• The developed domain-engineered PPLN crystal provides a robust platform for generating high-quality entangled photon pairs.
• The characterization confirms the suitability of the source for applications requiring high entanglement visibility.
• The observed interference phenomena validate the theoretical understanding of spectral correlations in entangled photon interferometry.