Photonic phase gates using Rydberg dark states

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.