Subnatural-linewidth polarization-entangled photon pairs with controllable temporal length

Area of Science:

• Quantum optics
• Atomic physics
• Quantum information science

Background:

• Spontaneous four-wave mixing (SFWM) is a key process for generating entangled photons.
• Narrow-bandwidth entangled photon sources are crucial for interfacing with atomic quantum memories.
• Previous methods often produced broader bandwidths, limiting their application in quantum networks.

Purpose of the Study:

• To develop an efficient experimental scheme for producing narrow-bandwidth, polarization-entangled photon pairs.
• To demonstrate the generation of all four Bell states using this scheme.
• To establish a foundation for robust quantum communication links.

Main Methods:

• Utilizing laser-cooled Rubidium-85 (85Rb) atomic ensemble for SFWM.
• Implementing a Mach-Zehnder interferometer to stabilize relative phase between SFWM paths.
• Achieving subnatural-linewidth bandwidth (as low as 0.8 MHz).

Main Results:

• Generation of polarization-entangled photon pairs with a bandwidth significantly narrower than the natural linewidth.
• Successful production of all four fundamental quantum states of entanglement (Bell states).
• Demonstration of an efficient experimental setup for high-fidelity entanglement generation.

Conclusions:

• The developed scheme provides ideal quantum information carriers for quantum networks.
• Narrow-bandwidth entangled photons facilitate efficient light-matter interaction for remote quantum node connection.
• This work advances the development of practical quantum communication and networking technologies.