Multi-functional atomic-ensemble quantum memory*

We present a system that embeds multiple functionalities in what was originally designed as a multiplexed quantum repeater node.  Our quantum memory is based on a cold atomic ensemble that uses multiplexing of wavevectors.  

Originally, we have proposed to use memory as a quasi-deterministic source of single photons. Since the source harnesses more than 1000 transverse modes, it is equivalent to 1000 SPDC sources synchronized with quantum memories.

The phase of spin waves stored in the memory can be modified. We have devised a new scheme where the phase is modified via an ac-Stark shift protocol with arbitrary spatial patterns. 

Such simple yet universal operations inside the memory can serve for optimizing the performance of the memory in the context of quantum repeaters, by implementing error-correction schemes inside the memory. 

In my presentation, I will describe the concepts behind embedding multiple functionalities in our quantum memory device and how they come together to create a very versatile system. With this, I will present the protocols for processing and interfering spin waves and generating single photons and Bell states demonstrated recently, and envisage the near-term new capabilities.