Generation of entangled photon pairs using small-coherence-time continuous wave pump lasers

Area of Science:

• Quantum optics
• Solid-state physics
• Photonics

Background:

• Entangled photon pair generation is vital for quantum information processing.
• Parametric downconversion (PDC) is a key source, but challenges exist with continuous-wave (cw) lasers of small coherence time.

Purpose of the Study:

• To investigate entangled photon pair generation using a compact, low-cost, two-crystal scheme with type-I phase matching.
• To analyze entanglement properties as a function of crystal length and pump coherence time.
• To explore a purification protocol for enhancing entanglement visibility.

Main Methods:

• Utilized a two-crystal scheme with type-I phase matching for PDC.
• Employed quantum state tomography to reconstruct the full density matrix.
• Varied crystal length and pump coherence time to study their effects.
• Implemented a purification protocol using a compensation crystal.

Main Results:

• Successfully generated entangled photon pairs from solid-state cw lasers with small coherence time.
• Characterized entanglement properties, showing dependence on crystal length and pump coherence time.
• Demonstrated improved entanglement visibility through the purification protocol.

Conclusions:

• The compact, low-cost setup is effective for generating entangled photons.
• Entanglement quality can be optimized by controlling experimental parameters.
• Purification protocols offer a viable route to enhance entanglement for practical applications.