Joint Quantum Institute, University of Maryland Department of Physics and National Institute of Standards and Technology, College Park, Maryland 20742, USA.
Nature. 2010 Jun 3;465(7298):590-3. doi: 10.1038/nature09071.
A network is frustrated when competing interactions between nodes prevent each bond from being satisfied. This compromise is central to the behaviour of many complex systems, from social and neural networks to protein folding and magnetism. Frustrated networks have highly degenerate ground states, with excess entropy and disorder even at zero temperature. In the case of quantum networks, frustration can lead to massively entangled ground states, underpinning exotic materials such as quantum spin liquids and spin glasses. Here we realize a quantum simulation of frustrated Ising spins in a system of three trapped atomic ions, whose interactions are precisely controlled using optical forces. We study the ground state of this system as it adiabatically evolves from a transverse polarized state, and observe that frustration induces extra degeneracy. We also measure the entanglement in the system, finding a link between frustration and ground-state entanglement. This experimental system can be scaled to simulate larger numbers of spins, the ground states of which (for frustrated interactions) cannot be simulated on a classical computer.
当节点之间的竞争相互作用阻止每个键被满足时，网络就会受阻。这种妥协是许多复杂系统行为的核心，从社交和神经网络到蛋白质折叠和磁性。受挫的网络具有高度简并的基态，即使在零温度下也存在过剩的熵和无序。在量子网络的情况下，受挫会导致大量纠缠的基态，从而支持奇异材料，如量子自旋液体和自旋玻璃。在这里，我们通过使用光学力精确控制三个被困原子离子系统中的受挫 Ising 自旋，实现了对其的量子模拟。我们研究了系统的基态，因为它从横向极化状态绝热演化，并且观察到受挫会引起额外的简并。我们还测量了系统中的纠缠，发现受挫与基态纠缠之间存在联系。这个实验系统可以扩展到模拟更多数量的自旋，其基态（对于受挫的相互作用）不能在经典计算机上进行模拟。
