Single-particle steering and nonlocality: The consecutive Stern-Gerlach Experiments

TL;DR

This paper demonstrates that consecutive Stern-Gerlach experiments can generate quantum nonlocality and steering, revealing new quantum effects in a classical-appearing setup and impacting our understanding of quantum correlations and entanglement.

Contribution

It provides the first fully quantum analysis showing that consecutive Stern-Gerlach experiments produce nonlocality and steering, challenging classical assumptions.

Findings

Consecutive Stern-Gerlach experiments generate quantum nonlocality.

Quantum steering can be observed in this setup.

The results link these effects to entanglement and quantum correlations.

Abstract

Quantum nonlocality and quantum steering are fundamental correlations of quantum systems which can not be created using classical resources only. Nonlocality describes the ability to influence the possible results of measurements carried out in distant systems, in quantum steering Alice remotely steers Bob's state. Research in nonlocality and steering possess a fundamental interest for the development of quantum information and in many applications requiring nonlocal resources like quantum key distribution. On the other hand, the Stern-Gerlach experiment holds an important place in the history, development and teaching of quantum mechanics and quantum information. In particular, the thought experiment of consecutive Stern-Gerlach Experiments is commonly used to exemplify the concept of non-commutativity between quantum operators. However, to the best of our knowledge, the consecutive Stern-Gerlach Experiments have not been treated in a fully quantum manner yet, and it is a widely accepted idea that atoms crossing consecutive Stern-Gerlach Experiments follow classical paths. Here we demonstrate that two consecutive Stern-Gerach Experiment generate nonlocality and steering, these nonlocal effects strongly modify our usual understanding of this experiment. Also, we discuss the implications of this result and its relation with the entanglement. This suggests the use of quantum correlations, of particles possessing mass, to generate nonlocal taks using this venerable experiment.