Multiparticle entanglement of neutral atoms by Rydberg excitation in an optical lattice

量子世界的一个基本性质是纠缠。如果两个物体之间没有明显的联系，但对其中一个物体的测量会对另一个物体产生影响，那么这两个物体就被称为纠缠。这种幽灵般的远距离行为可以用来实现量子密码学、量子隐形传态和量子计算等新技术。然而，为了利用纠缠态，我们需要能够以可控和灵活的方式产生和操纵纠缠。要克服的最大障碍之一是，纠缠态很快就会被与外部世界的相互作用所破坏。该项目的目的是在一个孤立的环境中产生纠缠态，使它们能够存活至少10秒。这将使我们有足够的时间来操纵纠缠态，并建立新一代利用量子纠缠的强大计算机的基石。我们将使用的方法是使用激光将原子冷却到绝对零度的百万分之一。在这些非常低的温度下，有可能使用激光束捕获原子，并形成由光束缚的超冷原子晶体。这些晶体被称为光学晶格，为研究量子物理提供了非常稳定的环境。为了产生纠缠，我们需要晶格中的原子相互作用。我们可以通过使用激光脉冲将原子激发到高激发态（称为里德堡态）来产生这种相互作用。在里德伯态中，原子产生一个电场，与任何相邻的里德伯原子相互作用。这种相互作用使原子纠缠在一起。我们可以使用额外的激光脉冲来检测纠缠的存在。一旦我们证明了纠缠，我们将使用纠缠态进行量子计算。除了计算进步的潜在令人兴奋的前景外，我们还将进一步加深对量子世界基本性质的理解。

A fundamental property of the quantum world is entanglement. Two objects are said to be entangled if a measurement on one has an effect on the other, even though there is no apparent connection between them. This spooky action at a distance can be employed to realise new technologies such as quantum cryptography, quantum teleportation and quantum computing. However, to exploit entangled states we need to be able to produce and manipulate entanglement in a controlled and flexible way. One of the biggest hurdles to overcome is that entangled states are very quickly destroyed by interactions with the external world. The aim of this project is to produce entangled states in an isolated environment where they will survive for at least 10 seconds. This will allow us plenty of time to manipulate the entangled states and establish the building blocks of a new generation of powerful computers exploiting on quantum entanglement.The method we will use is to use lasers to cool atoms to within a millionth of a degree of absolute zero. At these very low temperatures it is possible to trap atoms using laser beams and form crystals of ultra-cold atoms bound by light. These crystals are known as optical lattices and provide a very stable environment for studying quantum physics. To create entanglement we need the atoms in the lattice to interact with one another. We can create this interaction by exciting an atom using a laser pulse to a highly excited state, known as Rydberg state. In the Rydberg state, the atom creates an electric field with interacts with any neighbouring Rydberg atoms. This interaction allows the atoms to become entangled. We can detect the presence of entanglement using additional laser pulses. Once we have demonstrated entanglement, we will use entangled states to perform quantum computation. As well as the potentially exciting prospects for the advancement of computing, we will further enhance our understanding of the fundamental nature of the quantum world.