High Purity Single Photons Entangled with Barium Ions for Quantum Networking
[Thesis]
Crocker, Clayton
Monroe, Christopher
University of Maryland, College Park
2019
146 p.
Ph.D.
University of Maryland, College Park
2019
Increasing the number of qubits that can be controlled in a quantum system represents an essential challenge to the field of quantum computing. Quantum networks consisting of nodes for local information processing and photonic channels to distribute entanglement between different nodes represent a promising modular approach to achieve this scaling. Trapped atomic ions are an ideal candidate for quantum network nodes, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. In this work I will first discuss our established toolkit for using 171Yb+ and 138Ba+ ions individually or together within a quantum node. Next I will show how the 138Ba+ toolkit has been extended to allow for quantum operations in the 52D3/2 manifold. I will then demonstrate how we can generate ion-photon entanglement as a resource to connect separate nodes with a focus on some important improvements which will allow us to implement it as part of a larger network. These improvements include first the use of separate memory (171Yb+ ) and photon generating (138Ba+ ) ions. Additionally, the use of separate atomic lines within 138Ba+ for excitation and collection allows us to preserve integrity of this photonic interface by ensuring the purity of the single photons that are produced. To this end I demonstrate a single-photon source for quantum networking based on a trapped 138Ba+ ion with a single photon purity of g2(0) = (8.1 ± 2.3) × 10−5 without background subtraction. Trade-offs between the photonic generation rate and the memory-photon entanglement fidelity for the case of polarization photonic qubits are also examined and optimized by tailoring the spatial mode of the collected light. These techniques should be useful in constructing larger ion-photon networks.