Demonstration of analyzers for multimode photonic time-bin qubits

TL;DR

This paper presents two robust unbalanced interferometer approaches for analyzing multimode photonic time-bin qubits, demonstrating high entanglement verification and system throughput despite mode distortions, suitable for free-space quantum communication.

Contribution

Introduces two novel interferometer-based analyzers that are resilient to mode and polarization distortions in multimode quantum communication channels.

Findings

Achieved entanglement verification with visibility up to 0.85.

Demonstrated robustness against wavefront deformations and pointing errors.

Attained high system throughput of 0.74 with multimode fiber coupling.

Abstract

We demonstrate two approaches for unbalanced interferometers as time-bin qubit analyzers for quantum communication, robust against mode distortions and polarization effects as expected from free-space quantum communication systems including wavefront deformations, path fluctuations, pointing errors, and optical elements. Despite strong spatial and temporal distortions of the optical mode of a time-bin qubit, entangled with a separate polarization qubit, we verify entanglement using the Negative Partial Transpose, with the measured visibility of up to 0.85$\pm$0.01. The robustness of the analyzers is further demonstrated for various angles of incidence up to 0.2$^{\circ}$. The output of the interferometers is coupled into multimode fiber yielding a high system throughput of 0.74. Therefore, these analyzers are suitable and efficient for quantum communication over multimode optical channels.