Helicity-dependent quantum phases

光可以用两个特性来描述——它的传播方向和它的偏振。在日常生活中，后者通常影响不大，一个例外是，例如3D电影的两帧可以同时发送到每只眼睛，眼镜可以过滤掉给定的偏光，而保持另一只眼睛不变。这两幅图像的区别在于，一幅是左圆偏振的，这意味着光像左手开塞钻一样螺旋，而另一幅是右手偏振的，相反方向螺旋。这与称为螺旋度的光的特性密切相关，该特性将在本项目中用于设计称为光学晶格的技术工具的新示例。这使得仅使用光就可以捕获和悬浮原子网格。光学晶格通常有多种用途，包括制造人工分子和作为量子计算机的组成部分。这里设计的光学晶格将由在网格相邻点上具有相反螺旋度的光（就像棋盘一样）组成，因此放置在每个点上的螺旋度敏感原子将感受到来自晶格的不同影响。利用类似的想法，也可以设计出这样的晶格，在这种晶格中，构成光的电场和磁场以不同的方式与放置在晶格中的原子相互作用。这两种想法都可以用来影响原子相互作用的程度。在日常材料中，这种相互作用的强度在一定程度上决定了特定材料是固体、液体还是气体——这些都是物质相的例子。当相互作用强度达到某一临界值时，相发生变化（如熔融、沸腾），称为相变。利用螺旋度改变我们的光学晶格中的相互作用强度有望引起不同相之间的过渡，描述晶格中原子的集体行为。

Light is described by two characteristics - its direction of propagation and its polarisation. In everyday life the latter is usually of little consequence, an exception being for example the way the two frames of a 3D movie can be sent to each eye simultaneously glasses that filter out a given polarisation while leaving the other intact. The distinction between the two images is that one is left-circularly polarised, meaning that the light spirals like a left-handed corkscrew, while the other is right-handed, spiralling the other way. This is closely related to a property of light called the helicity, which will be used in this project to design a new example of a technological tool known as an optical lattice. These allow for the trapping and suspending a grid of atoms using only light. Optical lattices in general have a variety of uses, including making artificial molecules and acting as a component of a quantum computer.The optical lattices designed here will be made of light that has opposite helicity at neighbouring points in the grid (like a chessboard), so that helicity-sensitive atoms placed at each will feel a difference effect from the lattice. Using similar ideas it is also possible to design such lattices where the electric and magnetic fields that make up the light interact in different ways with the atoms placed in the lattice. Both of these ideas can be used to affect the degree to which the atoms interact with each other. In everyday materials, the strengths of such interactions are partly responsible for whether a particular material is a solid, liquid or gas - these are examples of phases of matter. When the interaction strength has some critical value, the phase changes (e.g. melting, boiling), this is known as a phase transition. Using helicity to vary the interaction strength in our optical lattice is expected to cause transitions between different phases describing the collective behaviour of the atoms in the lattice.