# Experimental minimum-error quantum-state discrimination in high dimensions

## TL;DR

This paper demonstrates the first experimental implementation of minimum-error quantum-state discrimination in high dimensions, achieving high accuracy for nonorthogonal state identification using optical transverse modes.

## Contribution

It provides the first experimental realization of minimum-error measurement for high-dimensional nonorthogonal states, advancing quantum communication techniques.

## Key findings

- Achieved high fidelity in discriminating states up to 21 dimensions
- Tested nearly 14,000 states with deviations below 3.6%
- Validated the scheme's suitability for quantum communication protocols

## Abstract

Quantum mechanics forbids perfect discrimination among nonorthogonal states through a single shot measurement. To optimize this task, many strategies were devised that later became fundamental tools for quantum information processing. Here, we address the pioneering minimum-error (ME) measurement and give the first experimental demonstration of its application for discriminating nonorthogonal states in high dimensions. Our scheme is designed to distinguish symmetric pure states encoded in the transverse spatial modes of an optical field; the optimal measurement is performed by a projection onto the Fourier transform basis of these modes. For dimensions ranging from D = 2 to D = 21 and nearly 14000 states tested, the deviations of the experimental results from the theoretical values range from 0.3% to 3.6% (getting below 2% for the vast majority), thus showing the excellent performance of our scheme. This ME measurement is a building block for high-dimensional implementations of many quantum communication protocols, including probabilistic state discrimination, dense coding with nonmaximal entanglement, and cryptographic schemes.