Postselection-Loophole-Free Bell Test Over an Installed Optical Fiber Network

Area of Science:

• Quantum Information Science
• Quantum Communication
• Experimental Quantum Physics

Background:

• Device-independent quantum communication necessitates loophole-free Bell inequality violations.
• Energy-time entangled photons are suitable for optical fiber communication due to their robustness.
• Previous in-field long-distance experiments with energy-time entanglement were affected by the postselection loophole.

Purpose of the Study:

• To demonstrate a loophole-free violation of the Clauser-Horne-Shimony-Holt Bell inequality.
• To utilize energy-time entangled photons for secure quantum communication over deployed optical fiber infrastructure.
• To overcome the postselection loophole in long-distance, in-field Bell tests.

Main Methods:

• Utilized energy-time entangled photons for quantum communication.
• Transmitted entangled photons over a 3.7 km deployed optical fiber network.
• Performed measurements to test the Clauser-Horne-Shimony-Holt Bell inequality.

Main Results:

• Achieved a violation of the Clauser-Horne-Shimony-Holt Bell inequality.
• Demonstrated the first spatially separated Bell violation free of the postselection loophole in an in-field, long-distance energy-time experiment.
• Successfully transmitted entangled photons over a 3.7 km optical fiber link.

Conclusions:

• The experiment represents a significant advancement towards fiber-based loophole-free Bell tests.
• The findings pave the way for secure quantum communication leveraging existing telecommunication infrastructure.
• This work addresses key challenges in implementing robust, long-distance quantum communication protocols.