GreenbergerHorneZeilinger

The Greenberger-Horne-Zeilinger (GHZ) state is a specific type of entangled quantum state involving three or more particles. It is named after the physicists Daniel Greenberger, Michael Horne, and Anton Zeilinger, who first described it in 1989. GHZ states are crucial in quantum information theory and fundamental tests of quantum mechanics.

A key characteristic of GHZ states is their strong non-classical correlations. For a three-particle GHZ state, for example, the state is a superposition of all particles being in one state (e.g., spin up) and all particles being in the opposite state (e.g., spin down). Measuring the state of one particle instantaneously influences the state of the others, regardless of the distance separating them. This phenomenon is a direct consequence of quantum entanglement.

GHZ states provide a stark demonstration of the non-locality predicted by quantum mechanics, contrasting sharply with classical intuitions. They have been experimentally realized and are fundamental resources for quantum computation, quantum communication protocols like quantum key distribution, and for exploring the foundations of quantum mechanics, including tests of Bell's inequalities. The robustness and unique properties of GHZ states make them a cornerstone in the development of quantum technologies.