The MICRON project focuses on the development of fast, scalable quantum networks by using miniature optical cavities to efficiently collect single photons from strontium ions.

SEM image of prototype cavity mirror substrate

Prototype 80 μm diameter cavity mirror substrate fabricated via Focused Ion Beam milling (in collaboration with Oxford HighQ)

One approach to producing large-scale ion trap quantum computers is to use a distributed architecture, connecting many simple ion trap 'nodes' in a quantum network. Entanglement between qubits in these physically separated traps is mediated by single photons collected from an ion in each node. We recently demonstrated a remote entanglement protocol of this sort in the Optical Networking experiment, generating Bell pairs between remote nodes at record-breaking rates and fidelities. However, despite this progress, the remote entanglement rate achievable using lens-based photon collection remains far lower than that of local gate operations, due to the ~10% photon collection efficiency.

To produce a truly scalable quantum network will require a step change in remote entanglement rate and thus photon collection efficiency. One of the most promising routes to achieving this is to place the network ion at the centre of an optical cavity. The Purcell enhancement of the emission that occurs into the cavity mode makes near unit-collection efficiencies possible in theory, but achieving this in practice is extremely technically challenging. By taking a new approach to microcavity fabrication and integrating this within the trap structure itself, we hope to demonstrate a robust approach to cavity-based networking and demonstrate remote entanglement at rates comparable to those of laser based entangling gates.