Laser Cooling of Ca to Bose Einstein condensation

由激光冷却和原子蒸发冷却制成的玻色-爱因斯坦凝聚体是已知最冷的物质，并开始找到广泛的应用，从理解流体到精确测量。迄今为止，大多数玻色斯坦凝聚物都是基于“单电子原子”，即原子结构是由带电核外的单个电子决定的。这通常会导致理想的激光冷却原子结构，但没有任何特别窄的谱线，这将是精确测量或光学时钟的理想选择。另一方面，双电子原子（如钙）提供与跃迁相关的窄线，其中电子自旋翻转，并且仍然相对容易激光冷却。原子钙的窄跃迁是本提议的关键。它将使我们能够用激光冷却原子，一直到玻色-爱因斯坦凝聚——由于散射在更宽的线上的光的重新吸收，这对其他原子是不可能做到的。其中一个重要的部分是将原子困在CO2激光器的强光场中，以防止它们在重力作用下下落，同时在窄线上缓慢冷却。激光直接冷却到凝结与依赖原子碰撞的传统方法有根本不同。因此，它将为凝析油的形成提供新的见解。CO2激光器为冷凝物提供了广泛的几何形状选择。我们可以在1、2和3维晶格中产生凝聚体，并研究许多独立产生的凝聚体在通过隔离屏障的量子力学隧道作用下被允许“看到”彼此时的相互作用。这项工作的最终愿景是在所谓的海森堡极限中使用窄原子跃迁进行精确测量（例如光学时钟）。这需要通过高度纠缠的多粒子态的玻色-爱因斯坦凝聚来准备，例如，处于基态和激发态叠加中的N原子，这样，如果发现一个处于基态，那么它们都处于基态，反之亦然。有了这样的状态，就有可能获得测量的精度，其尺度为1/N（海森堡极限），而不是泊松统计中的1/根号(N)。该项目将探索和开发一系列技术，以便在未来实现这些测量。

Bose-Einstein condensates made by laser cooling and evaporative cooling of atoms are the coldest known substance and are beginning to find a wide range of applications from understanding fluids to precision measurements. Most BoseEinstein condensate to date are based 'one-electron atoms', i.e. the atomic structure is determined by a single electron outside a charged core. This generally leads to an atomic structure ideal for laser cooling but without any particularly narrow spectral lines that would be ideal for precision measurement or optical clocks. On the other hand, the two-electron atoms (such a calcium) offer narrow lines associated with transitions, where an electron spin flips, and are still relatively easy to laser cool.The narrow transition in atomic calcium is key for the present proposal. It will enable us to laser cool the atoms all the way to Bose-Einstein condensation - something that has not been possible to do with other atoms due to the re-absorption of the light scattered on broader lines. An essential part of this is to trap the atoms in the strong light field of a CO2 laser in order to prevent them from falling under gravity while they are slowly cooled on the narrow line.The direct laser cooling to condensation is radically different from the traditional approach, which relies on atomic collisions. It will therefore provide new insight into the formation of condensates. The CO2 laser offers a wide choice of geometry for the condensate. We can generate condensates in 1, 2 and 3 dimensional lattices and study the interaction of many independently created condensates when they are allowed to 'see' each other due to quantum mechanical tunnelling through the separating barriers.The ultimate vision for this work is to use the narrow atomic transition for precision measurements (e.g. an optical clock) in what is known as the Heisenberg limit. That requires the preparation through Bose-Einstein condensation of highly entangled multi-particle states, e.g. N atoms in a superposition of ground and excited states such that if one is found in the ground state then they are all in the ground state or vice versa. With states like this it will be possible to obtain a precision on a measurement, that scales as 1/N (the Heisenberg limit) rather than the 1/sqrt(N) associated with Poissonian statistics. This project will explore and develop a range of technologies for the future realisation of such measurements.