[Paper Review] Full characterization of spin-orbit coupled photons via spatial-Stokes measurement

Bing‐Shi Yu, Haijun Wu+5 more|arXiv (Cornell University)|Jul 9, 2019

Orbital Angular Momentum in Optics32 references4 citations

TL;DR

This paper presents a spatial-Stokes measurement technique to fully characterize spin-orbit coupled (SOC) photons by directly measuring two spatial complex probability amplitudes and their relative phase within SOC states. By avoiding wavefront-flattening operations, the method preserves the photons' true SOC structure, enabling more accurate and precise wavefunction reconstruction than standard quantum state tomography.

ABSTRACT

Characterization and analysis of spin-orbit coupled (SOC) states, as a measurement problem, play a vital role in research on the modern optics and photonics based on structured light. Here, we demonstrate determination of photonic SOC states via spatial-Stokes measurement, in which two spatial complex probability amplitudes of spin-dependent spatial modes within SOC states and their relative (intramode) phase can be measured directly. Compared with the standard quantum-state tomography, by avoiding wavefront-flattening operations, the apparatus can completely record photons' realistic SOC structure, leading to a more accurate and precise determination of wavefunction. This simple and general approach for SOC state determination can provide a powerful toolkit for in-situ measuring photonic SOC state, characterizing the quality of SOC light source and associated geometric-phase devices.

Motivation & Objective

• To develop a direct, accurate method for characterizing spin-orbit coupled (SOC) photonic states in structured light.
• To overcome limitations of standard quantum state tomography that require wavefront-flattening operations, which distort the true SOC structure.
• To enable in-situ measurement of photonic SOC states and assessment of SOC light source quality.
• To provide a general and simple toolkit for characterizing geometric-phase devices based on structured photons.

Proposed method

• The method employs spatial-Stokes measurement to extract two spatial complex probability amplitudes associated with spin-dependent spatial modes in SOC states.
• It directly measures the relative (intramode) phase between the two spatial components of the SOC state.
• The approach avoids wavefront-flattening operations, preserving the original spatial and spinorial structure of the photons.
• The measurement setup is designed to record the full wavefunction of the SOC state in a single, non-invasive configuration.
• The technique leverages the spatial-Stokes parameters to reconstruct the complete quantum state of the photon.
• The method is general and applicable to various structured light beams with spin-orbit coupling.

Experimental results

Research questions

• RQ1 Can spatial-Stokes measurement provide a complete and accurate characterization of spin-orbit coupled photonic states without wavefront-flattening?
• RQ2 How does the spatial-Stokes method compare to standard quantum state tomography in preserving the true structure of SOC photons?
• RQ3 To what extent can this method enable in-situ measurement and quality assessment of SOC light sources?
• RQ4 Can this approach be generalized to characterize geometric-phase devices based on structured light?

Key findings

• The spatial-Stokes measurement method successfully captures the full wavefunction of spin-orbit coupled photons by measuring two spatial complex amplitudes and their relative phase.
• By avoiding wavefront-flattening, the method preserves the intrinsic SOC structure, leading to more accurate and precise wavefunction determination.
• The technique enables direct, in-situ measurement of photonic SOC states without requiring prior state reconstruction or complex calibration.
• The approach provides a general and robust toolkit for characterizing the performance of SOC light sources and geometric-phase optical devices.