Franson interferometer for characterizing highly non-degenerate correlated biphoton sources

Area of Science:

• Quantum optics
• Quantum information science
• Quantum communication

Background:

• Franson interferometers are crucial for Bell tests of time-energy entanglement.
• Verifying entanglement is key for quantum networks and secure quantum key distribution.
• Highly non-degenerate biphoton sources are needed for interfacing different quantum network types.

Purpose of the Study:

• To demonstrate a Franson interferometer with a highly non-degenerate time-energy entangled biphoton source.
• To achieve high visibility measurements for closing loopholes in Bell tests.
• To assess the potential of the source for quantum network applications.

Main Methods:

• Utilized a highly non-degenerate biphoton source with signal (810 nm) and idler (1550 nm) photons.
• Implemented a Franson interferometer setup to perform a Bell test.
• Measured single-channel and average visibilities across four output channels.

Main Results:

• Observed a single-channel visibility of V=0.992(6).
• Achieved an average visibility of V=0.984(3) over the four output channels.
• Demonstrated visibilities exceeding the threshold required to close the postselection loophole.

Conclusions:

• The demonstrated Franson interferometer successfully verifies time-energy entanglement.
• The high visibilities achieved overcome critical loopholes in Bell tests.
• The biphoton source's spectral characteristics enable potential interconnectivity between free-space and fiber optic quantum networks.