Postselection-Free Cavity-Enhanced Narrow-Band Orbital Angular Momentum Entangled Photon Source

Area of Science:

• Quantum Optics
• Quantum Information Science

Background:

• Cavity-enhanced spontaneous parametric down-conversion (SPDC) generates narrow-band photon pairs suitable for quantum memory.
• Existing methods require postselection to achieve entanglement, limiting efficiency and direct generation.

Purpose of the Study:

• To realize the first postselection-free cavity-enhanced narrow-band entangled photon pairs.
• To achieve entanglement in the orbital angular momentum (OAM) degree of freedom.

Main Methods:

• Utilized an OAM-conservation SPDC process within a precisely controlled cavity supporting high-order OAM modes.
• Demonstrated deterministic entanglement transfer from OAM to polarization.
• Generated OAM-polarization hyperentangled photon pairs via interference on a polarizing beam splitter (PBS).

Main Results:

• Achieved direct generation of OAM entangled photon pairs with a measured linewidth of 13.8 MHz and fidelity of 0.969(3).
• Transferred OAM entanglement to polarization entanglement with a fidelity of 0.948(2).
• Produced narrow-band OAM-polarization hyperentangled photon pairs with a fidelity of 0.850(2).

Conclusions:

• The proposed method provides an efficient and promising approach for creating narrow-band entangled photon sources.
• This advancement is crucial for memory-based long-distance quantum communication and quantum networks.
• The novel cavity may also find applications in cavity-based light-matter interactions.