标题： 通过一个光子产生的三千个原子的负Wigner函数纠缠 显示英文标题

标题： Entanglement with Negative Wigner Function of Three Thousand Atoms Heralded by One Photon

摘要： 量子力学相关的（纠缠的）多粒子状态在量子信息、量子计算和量子计量学中受到关注。 在实验上已经实现了具有计量学价值的大原子集合的纠缠态，但这些态表现出高斯自旋分布函数，其Wigner函数为非负值。 在小离子集合中已经产生了非高斯纠缠态，并且最近在大原子集合中也实现了这一点。 在这里，我们通过与非常弱的激光脉冲相互作用，在一个大的原子集合中生成纠缠；值得注意的是，检测到一个光子可以将数千个原子制备成一种纠缠态。 我们重建了一个负值的Wigner函数，这是非经典性的重要特征，并验证了纠缠深度（相互纠缠原子的最小数量）为3100个原子中的2910(190)。 这是首次在一个包含多个粒子的集合中实现负Wigner函数或几乎所有原子的相互纠缠。 虽然所实现的状态纯度略低于由纠缠引起的计量增益阈值，但进一步的技术改进应该能够生成超过该阈值的状态，以及更复杂的薛定谔猫态，用于量子计量学和信息处理。 更一般地，我们的结果展示了预告方法在生成纠缠方面的强大能力，并说明单个光子中包含的信息可以显著改变大型系统的量子态。 显示英文摘要

摘要： Quantum-mechanically correlated (entangled) states of many particles are of interest in quantum information, quantum computing and quantum metrology. Metrologically useful entangled states of large atomic ensembles have been experimentally realized, but these states display Gaussian spin distribution functions with a non-negative Wigner function. Non-Gaussian entangled states have been produced in small ensembles of ions, and very recently in large atomic ensembles. Here, we generate entanglement in a large atomic ensemble via the interaction with a very weak laser pulse; remarkably, the detection of a single photon prepares several thousand atoms in an entangled state. We reconstruct a negative-valued Wigner function, an important hallmark of nonclassicality, and verify an entanglement depth (minimum number of mutually entangled atoms) of 2910(190) out of 3100 atoms. This is the first time a negative Wigner function or the mutual entanglement of virtually all atoms have been attained in an ensemble containing more than a few particles. While the achieved purity of the state is slightly below the threshold for entanglement-induced metrological gain, further technical improvement should allow the generation of states that surpass this threshold, and of more complex Schrodinger cat states for quantum metrology and information processing. More generally, our results demonstrate the power of heralded methods for entanglement generation, and illustrate how the information contained in a single photon can drastically alter the quantum state of a large system.