State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China.
Collaborative Innovation Center of Quantum Matter, Beijing, China.
Science. 2017 Feb 10;355(6325):620-623. doi: 10.1126/science.aag1106.
Many-body entanglement is often created through the system evolution, aided by nonlinear interactions between the constituting particles. These very dynamics, however, can also lead to fluctuations and degradation of the entanglement if the interactions cannot be controlled. Here, we demonstrate near-deterministic generation of an entangled twin-Fock condensate of ~11,000 atoms by driving a arubidium-87 Bose-Einstein condensate undergoing spin mixing through two consecutive quantum phase transitions (QPTs). We directly observe number squeezing of 10.7 ± 0.6 decibels and normalized collective spin length of 0.99 ± 0.01. Together, these observations allow us to infer an entanglement-enhanced phase sensitivity of ~6 decibels beyond the standard quantum limit and an entanglement breadth of ~910 atoms. Our work highlights the power of generating large-scale useful entanglement by taking advantage of the different entanglement landscapes separated by QPTs.
多体纠缠态通常通过系统演化来产生，这得益于构成粒子之间的非线性相互作用。然而，如果无法控制相互作用，这些动力学过程也可能导致纠缠的涨落和退相干。在这里，我们通过两次连续的量子相变（QPT）驱动自旋混合，展示了近确定性地产生约 11000 个原子的纠缠双费米子凝聚体。我们直接观察到了 10.7 ± 0.6 分贝的数压缩和 0.99 ± 0.01 的归一化集体自旋长度。这些观测结果表明，我们可以推断出纠缠增强的相位灵敏度约为 6 分贝，超过了标准量子极限，并且纠缠宽度约为 910 个原子。我们的工作强调了通过利用 QPT 分隔的不同纠缠景观来产生大规模有用纠缠态的优势。
