Robust, high brightness, degenerate entangled photon source at room temperature.

Area of Science:

• Quantum Optics
• Photonics
• Quantum Information Science

Background:

• Entangled photon sources are crucial for quantum communication and computation.
• Existing sources often require complex setups, cryogenic cooling, or are limited in brightness.
• Developing compact, robust, and high-brightness sources is a key research objective.

Purpose of the Study:

• To report a compact, simple, and robust high-brightness entangled photon source operating at room temperature.
• To characterize the spectral brightness and entanglement properties of the source.
• To demonstrate the suitability of the source for quantum communication applications.

Main Methods:

• Utilized a 30-mm-long periodically-poled potassium titanyl phosphate (PPKTP) crystal for spontaneous parametric down-conversion (SPDC).
• Employed a novel system architecture integrating a Sagnac interferometer and polarizing optical elements.
• Studied the dependence of pump focusing on photon brightness and fiber coupling efficiency.

Main Results:

• Achieved a spectral brightness of ~0.41 MHz/mW/nm for multi-mode fiber coupling, the highest reported for a CW laser-pumped bulk crystal source.
• Generated polarization-entangled photon states with a high Bell's parameter (S=2.63±0.02), violating Bell's inequality by 32 standard deviations.
• Demonstrated a high fidelity of 0.975 for entangled states detected in single-mode fiber, even without phase compensation.

Conclusions:

• The developed entangled photon source is compact, robust, and operates at room temperature.
• Its high spectral brightness and strong entanglement properties make it ideal for practical quantum communication experiments.
• This work represents a significant advancement in the development of practical quantum technologies.