Entanglement swapping with autonomous polarization-entangled photon pairs from a warm atomic ensemble

Area of Science:

• Quantum Information Science
• Quantum Communication
• Atomic Physics

Background:

• Entanglement swapping is vital for scalable quantum networks and communication.
• Practical implementation requires autonomous entanglement sources and joint Bell-state measurements (BSM).

Purpose of the Study:

• To experimentally demonstrate entanglement swapping between two independent photon sources.
• To confirm the violation of Bell's inequality using the generated entanglement.

Main Methods:

• Utilized spontaneous four-wave mixing (SFWM) in a Doppler-broadened atomic ensemble of Rubidium-87 (${^{87}}{\rm Rb}$) to generate photon pairs.
• Performed a joint Bell-state measurement (BSM) on photons from two independent sources.
• Estimated the S parameter of the Clauser-Horne-Shimony-Holt (CHSH) form of Bell's inequality.

Main Results:

• Successfully demonstrated entanglement swapping between two independent polarization-entangled photon-pair sources.
• Confirmed the violation of the Bell-CHSH inequality with an estimated S parameter of ${2.32} \pm {0.07}$.
• Achieved statistical significance of 4.5 standard deviations for the Bell inequality violation.

Conclusions:

• The experimental demonstration of entanglement swapping is a significant advancement for quantum networks.
• This work paves the way for practical, scalable quantum communication systems.
• The successful violation of Bell's inequality validates the entanglement swapping protocol in this setup.