We propose an entanglement-creation scheme in a multi-atom ensemble trapped in an optical cavity, named entanglement amplification, converting unentangled states into entangled states and amplifying less-entangled ones to maximally entangled Greenberger-Horne-Zeilinger (GHZ) states whose fidelity is logarithmically dependent on the atom number and robust against common experimental noises. 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.

我们提出了一种在光腔中捕获的多原子集合中的纠缠-创建方案，称为纠缠放大，将未纠缠的状态转换为纠缠的状态，并将不纠缠的状态放大为保真度为最大的格林伯格-霍恩-泽林格（GHZ）状态对数依赖于原子数，并且对常见的实验噪声具有鲁棒性。该方案始于以相干自旋状态初始化的多原子集合。通过移动特定迪克态的能量，我们将集合体的希尔伯特空间分成两个独立的子空间，以将相干自旋态撕成两个分量，从而引入了纠缠。之后，我们利用隔离的子空间通过将两个分量相干分离来进一步增强纠缠。