Quantum coherence of spatial photonic qudits: experimental measurement and path-marker analysis

TL;DR

This paper experimentally measures the quantum coherence of high-dimensional spatial photonic states using the l1 norm, validating a theoretical method and proposing an alternative approach for certain states.

Contribution

It provides the first experimental measurement of the l1 norm of spatial photonic qudits and discusses the use of interference patterns and path-markers for coherence assessment.

Findings

Successful experimental measurement of l1 norm for qutrit states.

Validation of the theoretical method for coherence measurement.

Proposal of an alternative method when assumptions are not met.

Abstract

Discussions about quantum interference, indistinguishability and superpostion between quantum states goes back to the beginning of quantum mechanics, but the theoretical problem concerning quantitative measures for quantum coherence was only recently solved by Baumgratz et al. [Phys. Rev. Lett. 113 140401 (2014)]. Since then many works have explored one of the possible coherence measures, the l1 norm, which has not yet been experimentally obtained for spatial photonic states in high dimensions. In this article we study states prepared with photons crossing multiple slits and implement the theoretical proposal of T. Paul and T. Qureshi [ Phys. Rev. A 95 042110 (2017)] to determine experimentally the l1 norm of qutrit states. We analyze the method validity and present an alternative for states in which one of their assumptions does not apply. We also discuss the requirements necessary for using an interference pattern for measuring quantum coherence of qudits by treating the measure-operator that describe the detection optical configuration as path-markers, relating them with the quantum coherence determination.