Quantum state tomography of orbital angular momentum photonics qubits via a projection-based technique

TL;DR

This paper introduces a projective measurement technique for quantum state tomography of photonic qubits encoded in orbital angular momentum, enabling precise characterization at the single-photon level.

Contribution

It presents a novel setup using spatial mode projection with fork holograms and single-mode fibers for quantum state tomography of OAM photonic qubits.

Findings

Effective reconstruction of quantum states demonstrated

Detailed calibration and measurement procedures provided

Potential for extension to higher-dimensional OAM spaces

Abstract

While measuring the orbital angular momentum state of bright light beams can be performed using imaging techniques, a full characterization at the single-photon level is challenging. For applications to quantum optics and quantum information science, such characterization is an essential capability. Here, we present a setup to perform the quantum state tomography of photonic qubits encoded in this degree of freedom. The method is based on a projective technique using spatial mode projection via fork holograms and single-mode fibers inserted into an interferometer. The alignment and calibration of the device is detailed as well as the measurement sequence to reconstruct the associated density matrix. Possible extensions to higher-dimensional spaces are discussed.