Can Randomly Structured Metasurfaces Be Used for Quantum Tomography of High-Dimensional Spatial Qudits?

TL;DR

This study investigates whether randomly structured metasurfaces can effectively perform quantum tomography of high-dimensional spatial qudits, demonstrating promising results for up to about 10 states through extensive numerical simulations.

Contribution

The paper provides the first large-scale numerical analysis showing that random metasurfaces can be used for quantum tomography of spatial qudits, expanding their potential application scope.

Findings

Random metasurfaces perform well with sufficient detector redundancy.

Effective for up to approximately 10 spatial qudit states.

Insights into optimizing metasurfaces for multiphoton quantum measurements.

Abstract

Reconstructing the density matrix of the quantum state of photons through a tomographically complete set of measurements, known as quantum state tomography, is an essential task in nearly all applications of quantum science and technology, from quantum sensing to quantum communications. Recent advances in optical metasurfaces enable the design of ultrathin nanostructured optical elements performing such state tomography tasks, promising greater simplicity, miniaturization, and scalability. However, reported metasurfaces on this goal were limited to a small Hilbert dimension, e.g., polarization qubits or spatial qudits with only a few states. When scaling up to higher-dimensional qudit tomography problems, especially those involving spatial qudits, a natural question arises: whether a metasurface with randomized nanostructures is sufficient to perform such qudit tomography, achieving optimal conditions. In this work, we attempt to answer this question through a set of numerical experiments with random metasurfaces, utilizing large-scale simulations of over 16,000 distinct metasurfaces each exceeding 200 wavelengths in size. We show that with sufficient redundancy in the number of detectors, random metasurfaces perform reasonably well in quantum photonic spatial qudit tomography encoded in Hermite-Gaussian states for up to approximately 10 states. Furthermore, we discuss additional considerations for optimizing metasurfaces in multiphoton cases. Our work opens a pathway toward computationally efficient, miniaturized, and error-tolerant quantum measurement platforms.