CPM Seminar

Hybrid Systems for Quantum Networks

Chris Wilson

IQC
University of Waterloo

In recent years, quantum information science has advanced rapidly, with quantum cryptography systems already commercially available. These systems are an example of quantum channels, serving mainly to distribute quantum information. There is a significant effort underway to combine these quantum channels with quantum nodes that would offer basic memory, processing and routing capability. The combination of these channels and nodes would create a fully quantum network. An obvious requirement of a quantum channel is the ability to distribute quantum information over large distances. This typically implies the use of optical photons as information carriers. This presents a problem when trying to implement a quantum node, as the interaction of photons with themselves is vanishingly small. Without interactions, photons cannot be controlled. This problem can be overcome by using matter as an intermediary, exploiting the strong interactions of electrons for instance.This suggests a hybrid architecture for quantum networks: using optical photons for long distance communication (quantum channels) and superconducting circuits operating in the microwave regime for processing and routing (quantum nodes). I will present experimental work aimed at enabling a future hybrid quantum network. First, I will present work developing quantum nodes, where our basic system is a single artificial atom (qubit) strongly coupled to a coplanar waveguide. In this model system for 1D quantum electrodynamics, we have demonstrated a single-photon router and the generation on nonclassical microwave states. I will then discuss work towards a hybrid quantum interface, with the goal of coherently converting between optical and microwave photons. Such an interface is needed to connect our quantum nodes to optical quantum channels. We are pursuing an approach based on ensembles of atoms spins doped into crystals. In particular, I will present preliminary results on crystals doped with rare-earth ions (REI), such as Er and Nd, coupled to superconducting cavities.