Ion trap-integrated optical cavities for fast networked quantum computation

The QCS vision of quantum computing using distributed modular processors (networked 'nodes') depends upon the rapid production of remote entanglement between nodes. The current state-of-the-art rate is our NQIT result of 182 Hz [Phys. Rev.

Lett. 124, 110501 (2020)] and any further performance increases in similar systems will be modest, due to the limited photon collection efficiency achievable via refractive optics. Optical cavities provide an elegant route to photon collection with near-unit efficiency, and are likely to become crucial components as a useful networked processor will require much higher remote entanglement rates.

Critically, it will also need simpler and more reliable nodes, with a design amenable to large-scale fabrication and requiring minimal maintenance and calibration. Aims and Objectives:

The MICRON-QC project (ERC-selected/UKRI-funded; 5Y from Jun 2023) builds upon foundations laid during the NQIT and QCS Hubs and complements and extends their programmes of quantum networking research. The project aims to construct the first reconfigurable network of trapped ion processors linked by single photons, ultimately consisting of 5 nodes. We will demonstrate all elements needed for efficient large-scale networked computation including: a flying qubit suitable for high-fidelity long-range transmission; a reconfigurable network enabling any-to-any node connectivity; and the functionality in each node required to assemble arbitrary entangled network graph states.

We will construct cavity-based network interfaces at each node yielding near-deterministic ion-photon entanglement and allowing remote ion-ion entanglement creation at 100kHz rates, close to that of local gates. While the 5-node network constructed in this project will enable many fascinating experiments, the principal objective will be to prove that a network of hundreds or more nodes is within reach.

We will demonstrate all elements needed for efficient large-scale networked computation including: a flying qubit suitable for high-fidelity long-range transmission; a reconfigurable network enabling any-to-any node connectivity; and the functionality in each node required to assemble arbitrary entangled network graph states. We will construct cavity-based network interfaces at each node yielding near-deterministic ion-photon entanglement and allowing remote ion-ion entanglement creation at 100kHz rates, close to that of local gates

Novelty of the research methodology:

In recent years our team has pioneered a number of ground-breaking approaches to the design and construction of ion-trap network nodes, which will integrate passively aligned microcavities and other functional modules within the structure of the ion trap chip itself. Combined with novel approaches to packaging and optical delivery, this will yield nodes of simple, robust construction, enabling near-autonomous operation.

The student would join at an exciting stage, with the supporting infrastructure and experimental systems in place. The student would be able to make significant contributions to the project in characterising the performance of one or more ion trap designs, applying this experience in helping to construct the first integrated-cavity node, before using this system to produce high-rate ion-photon entanglement.

In their second and third years, they would help build at least one more node and use this to demonstrate remote ion-ion entanglement at rates comparable to those of local gates, a milestone result for networked quantum computing. The work involved will be varied, ranging from ion trap design and modelling, to theoretical quantum optics, UHV techniques and cutting-edge experimental control.

However, the variety of elements involved and the support of several PDRAs mean the emphasis of project can be tailored to suit the strengths and interests of the student in question. This project falls within the EPSRC quantum tech/physical sciences research area.