On the Direct Generation of Ion-Photon Entanglement at Telecom Wavelengths in 171Yb+

Abstract

Trapped atomic ions are one of the leading quantum information platforms especially for quantum computing. A source of high-fidelity ion-entangled photons can be used to entangle remote quantum nodes. The strong coupling of an ion to an optical cavity mode also enables a range of quantum networking protocols. However, both paths are technically complex. This thesis investigates quantum networking based on trapped ytterbium ions in optical cavities for single photon generation. We first propose and evaluate a cavity-mediated scheme for ion-entangled photons using the $1345\text{ nm}$ and $1650\text{ nm}$ telecom-wavelength transitions in $\mathrm{Yb^{+}}$. We implement a $6\text{ K}$-cryogenic ion-trap-integrated optical Fabry-Pérot cavity with a 56,000 finesse. One cavity mirror, a meta-material lens and a single-mode fiber are assembled as a compact monolithic in-vacuum package. The package remains aligned to the cavity from $293\text{ K}$ to $6\text{ K}$. The cavity is actively length-stabilized to suppress vibration-induced linewidth broadening from the closed-cycle helium cryogenic system. We demonstrate spatial overlap and interaction between the cavity mode with a trapped ytterbium ion on the $1345\text{ nm}$ transition. To mitigate surface charging on dielectric surfaces, we investigate ZnO transparent conductive oxides on top of optical cavity coatings. At $1650\text{ nm}$ we observe a 20,000 finesse in a cavity coated with a $30\text{ nm}$ ZnO layer. This film exhibits $0.01\text{ \ensuremath{\Omega}\ensuremath{\cdot}cm}$ surface resistivity at DC. In support of this work I advanced state of the art in Pound-Drever-Hall locking by describing an error-budget type that accounts for PDH phase lag and documenting a little-known source of systematic error in PDH offset locks. Together, these developments advance the state of the art in ion-cavity systems and ion-based quantum networking.