JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309, USA.
Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
Nature. 2015 Nov 12;527(7577):208-11. doi: 10.1038/nature16073. Epub 2015 Nov 2.
To advance quantum information science, physical systems are sought that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of either Coulomb interactions between ions or dipolar interactions between Rydberg atoms. Although such interactions allow fast quantum gates, the interacting atoms must overcome the associated coupling to the environment and cross-talk among qubits. Local interactions, such as those requiring substantial wavefunction overlap, can alleviate these detrimental effects; however, such interactions present a new challenge: to distribute entanglement, qubits must be transported, merged for interaction, and then isolated for storage and subsequent operations. Here we show how, using a mobile optical tweezer, it is possible to prepare and locally entangle two ultracold neutral atoms, and then separate them while preserving their entanglement. Ground-state neutral atom experiments have measured dynamics consistent with spin entanglement, and have detected entanglement with macroscopic observables; we are now able to demonstrate position-resolved two-particle coherence via application of a local gradient and parity measurements. This new entanglement-verification protocol could be applied to arbitrary spin-entangled states of spatially separated atoms. The local entangling operation is achieved via spin-exchange interactions, and quantum tunnelling is used to combine and separate atoms. These techniques provide a framework for dynamically entangling remote qubits via local operations within a large-scale quantum register.
为了推动量子信息科学的发展，人们一直在寻找满足创建和保存量子纠缠严格要求的物理系统。在原子物理学中，通过离子间的强、长程库仑相互作用或里德堡原子间的偶极相互作用，通常可以实现稳健的双qubit 纠缠。尽管这种相互作用允许快速量子门操作，但相互作用的原子必须克服与环境的耦合以及量子比特之间的串扰。局部相互作用，如需要大量波函数重叠的相互作用，可以缓解这些不利影响；然而，这种相互作用带来了一个新的挑战：为了分配纠缠，量子比特必须被传输、合并进行相互作用，然后隔离进行存储和后续操作。在这里，我们展示了如何使用移动光学镊子来制备和局部纠缠两个超冷中性原子，然后在分离它们的同时保持它们的纠缠。基态中性原子实验已经测量了与自旋纠缠一致的动力学，并检测到了与宏观可观测量的纠缠；我们现在能够通过施加局部梯度和奇偶测量来证明两粒子的位置分辨相干性。这个新的纠缠验证协议可以应用于任意空间分离原子的自旋纠缠态。局部纠缠操作是通过自旋交换相互作用实现的，而量子隧穿则用于组合和分离原子。这些技术为通过大规模量子寄存器中的局部操作动态纠缠远程量子比特提供了一个框架。
