Creation of 2000-atom Greenberger-Horne-Zeilinger states by entanglement amplification

TL;DR

This paper introduces a new entanglement amplification method that converts unentangled or weakly entangled multi-atom states into highly entangled 2000-atom GHZ states with high fidelity, suitable for quantum metrology.

Contribution

The paper presents a novel scheme for creating large-scale GHZ states by entanglement amplification in multi-atom ensembles, achieving high fidelity in an experimentally feasible setup.

Findings

2000-atom GHZ states achieved with >80% fidelity

Scheme converts unentangled states into maximally entangled states

Method is feasible with current optical cavity technology

Abstract

We propose a novel entanglement-creation scheme in a multi-atom ensemble, named entanglement amplification, which converts unentangled states into entangled states and amplifies less-entangled ones to maximally-entangled Greenberger-Horne-Zeilinger (GHZ) states. The scheme starts with a multi-atom ensemble initialized in a coherent spin state. By shifting the energy of a particular Dicke state, we break the Hilbert space of the ensemble into two isolated subspaces to tear the coherent spin state into two components so that entanglement is introduced. After that, we utilize the isolated subspaces to further enhance the entanglement by coherently separating the two components. By single-particle Rabi drivings on atoms in a high-finesse optical cavity illuminated by a single-frequency light, 2000-atom GHZ states can be created with a fidelity above 80% in an experimentally achievable system, making resources of ensembles at Heisenberg limit practically available for quantum metrology.