Robust and bright polarization-entangled photon sources exploiting non-critical phase matching without periodic...

Area of Science:

• Quantum Information Science
• Photonics
• Quantum Optics

Background:

• Entangled photon sources are crucial for quantum computation, communication, and metrology.
• Periodically poled (PP) crystals are commonly used for bright photon generation via quasi-phase matching (QPM).
• Fabricating uniform micron-scale periodic structures in PP crystals presents significant technical challenges, limiting crystal thickness.

Purpose of the Study:

• To develop a robust and bright polarization-entangled photon source.
• To overcome the limitations of traditional periodically poled crystals.
• To enable scalable and practical photonic quantum information applications.

Main Methods:

• Utilized non-critical phase matching (NCPM) in a bulk KTP crystal.
• Integrated the crystal within a Sagnac interferometer setup.
• Avoided the need for periodic poling structures.

Main Results:

• Achieved a robust and bright polarization-entangled photon source.
• Demonstrated tolerance to variations in pump incidence angles and temperature.
• Experimentally generated the four Bell states with high brightness (25.1 kHz/mW at 1079 nm).
• Attained purity, concurrence, and fidelity values close to 0.99.

Conclusions:

• The NCPM approach offers a significant brightness enhancement (theoretically ~2.5-fold) over QPM.
• The absence of periodic poling allows for larger crystal cross-sections, improving practicality.
• This scheme serves as a key building block for scalable photonic quantum information applications.