Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Nat Commun. 2012 Jun 6;3:882. doi: 10.1038/ncomms1872.
Topological phases exhibit some of the most striking phenomena in modern physics. Much of the rich behaviour of quantum Hall systems, topological insulators, and topological superconductors can be traced to the existence of robust bound states at interfaces between different topological phases. This robustness has applications in metrology and holds promise for future uses in quantum computing. Engineered quantum systems--notably in photonics, where wavefunctions can be observed directly--provide versatile platforms for creating and probing a variety of topological phases. Here we use photonic quantum walks to observe bound states between systems with different bulk topological properties and demonstrate their robustness to perturbations--a signature of topological protection. Although such bound states are usually discussed for static (time-independent) systems, here we demonstrate their existence in an explicitly time-dependent situation. Moreover, we discover a new phenomenon: a topologically protected pair of bound states unique to periodically driven systems.
拓扑相表现出现代物理学中一些最引人注目的现象。量子霍尔系统、拓扑绝缘体和拓扑超导体的许多丰富行为都可以追溯到不同拓扑相之间界面处存在稳定的束缚态。这种稳定性在计量学中有应用，并有望在未来的量子计算中得到应用。工程量子系统——特别是在光子学中，其中可以直接观察到波函数——为创建和探测各种拓扑相提供了多功能平台。在这里，我们使用光子量子漫步来观察具有不同体拓扑性质的系统之间的束缚态，并证明它们对微扰的鲁棒性——这是拓扑保护的一个特征。尽管通常在讨论静态（时不变）系统的束缚态，但在这里我们证明了它们在显式时变情况下的存在。此外，我们发现了一个新现象：一种独特的周期性驱动系统中的拓扑保护束缚态对。
