Single Rare-Earth Ions in Solid-State Hosts: A Platform for Quantum Networks

Citation

Ruskuc, Andrei (2024) Single Rare-Earth Ions in Solid-State Hosts: A Platform for Quantum Networks. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ecn2-pp53. https://resolver.caltech.edu/CaltechTHESIS:10202023-123922325

Abstract

Solid-state defects have emerged as leading candidates for quantum network nodes due to their compatibility with scalable device engineering and local nuclear spins for quantum processing. Rare-earth ions in crystalline hosts are particularly attractive due to their long optical and spin coherence times at cryogenic temperatures. However, until recently, detection and utilization of single rare-earth ions in quantum technologies has been hindered by their inherently weak optical transitions. In this thesis I present progress towards realizing a novel quantum network node architecture using single ¹7¹Yb³⁺ ions in YVO₄, coupled to a nanophotonic cavity.

First, we demonstrate coherent operation of single ¹7¹Yb³⁺ ions as optically addressed qubits. To do this, we leverage first order insensitivity of optical and spin transitions to electric and magnetic fields, thereby protecting the qubits from environmental noise. We demonstrate initialization, high fidelity control and readout of a hyperfine spin qubit with long quantum storage times. We also characterize the optical transitions and find a lifetime-limited echo coherence, thereby enabling a coherent spin-photon interface.

Next, we focus on realizing an auxiliary quantum register. The high-fidelity spin control of our ¹7¹Yb³⁺ qubit is leveraged to access local nuclear spins. These spins comprise a dense ensemble which serves as a deterministic quantum resource. We utilize Hamiltonian engineering to generate tailored interactions, enabling polarization, coherent control and preparation of many-body nuclear spin states. Finally, we implement a spin-wave based memory protocol and demonstrate storage and retrieval of quantum states.

Moving beyond a single quantum node, in the final section of this thesis we will realize a small-scale quantum network using this platform. As a first step we demonstrate time-resolved quantum interference between photons emitted by ions in two separate devices. Then, we demonstrate a novel heralded entanglement protocol which incorporates optical dynamical decoupling and frequency erasure via precise photon detection. This protocol counteracts both static and dynamic inhomogeneity in the ions’ optical transition frequencies, thereby enabling entanglement generation between any pair of qubits in a scalable fashion.

These results showcase single rare-earth ions as a promising platform for the future quantum internet.

Thesis Files