Photonic phase gates using Rydberg dark states

在自由空间中，两束光相互穿过，没有任何相互作用。这种特性使得光子（光的组成部分）成为非常强大的信息载体，并为光通信和其他光子技术提供了基础。然而，如果人们能找到一种方法使光子相互作用，这将创造一个全新的光子设备和行业。该项目的目标是制造一种称为光子相位门的设备，其中一个光子引起另一个光子的延迟。使光子相互作用的第一步是使用原子作为吸收体来捕获它们。如果原子相互作用，那么人们可以将这些原子相互作用映射到光子上，然而，原子之间的相互作用也非常弱。为了解决这个问题，我们计划将原子激发到所谓的里德伯态，在这种状态下，电子远离原子核。在这些里德伯态中，原子具有非常大的相互作用。在我们的提议中，我们计划使用一系列激光脉冲，首先将入射光子存储为原子激发，然后通过将它们激发到里德伯态来使原子相互作用，最后读出初始光子。通过这种方式，我们可以将里德伯原子之间的强相互作用映射到光子上，从而实现光子相位门。

In free space, two light beams pass through one another without any interaction. This property makes photons (the constituents of light) very robust carriers of information and provides the basis for optical communications and other photonic technologies. However, if one could find a way to make photons interact this would create a whole new class of photonic devices and industries. The goal of this project is to make a device called a photonic phase gate, where one photon induces a delay in another. The first step towards making photons interact is to trap them using atoms as an absorber. If the atoms interact then one could map these atomic interactions onto the photons, however, the interaction between atoms is also very weak. To get around this problem we plan to excite the atoms to a so called Rydberg state where the electron is moved far away from the nucleus. In these Rydberg states atoms have very large interactions. In our proposal we plan to use a sequence of laser pulses to first store the incident photons as atomic excitations, then make the atoms interact by exciting them to the Rydberg state and finally to read out the initial photons. In this way we can map the strong interaction between Rydberg atoms onto the photons and thereby realise a photonic phase gate.