Hybrid-integrated photonics platform for quantum networks based on defects in diamond

Abstract

Optically active defects in solid-state hosts such as diamond are a promising platform for quantum technologies. In such a platform, quantum information is encoded in the localized spin states of the defect system while photons are utilized to mediate the long-range transfer of information over the quantum network. The efficient interfacing of network photons and individual defects is consequently a fundamental requirement. This may be achieved by integrating defects into photonic circuits and leveraging the enhanced control afforded by cavity quantum electrodynamics (QED). At the same time, this approach also offers a straightforward means of scalability as these circuits can be densely packed with all the necessary functionalities onto a single chip. The development of a photonics platform capable of realizing such functionality and scalability, however, remains elusive. In this thesis we develop a scalable hybrid-integrated quantum photonics platform based on gallium phosphide (GaP)-on-diamond. We demonstrate the first integrated photonic devices in boron-doped GaP --- a scalable source of GaP grown commercially at 12-inch wafer scale --- defining a path forward for the development of large-scale GaP-on-diamond photonics. Leveraging the strong nonlinear properties of GaP, we describe novel nonlinear photonic devices which utilize resonant enhancement to achieve high-efficiency frequency conversion in compact and scalable integrated devices. We then develop a technique for enhancing the bandwidth of these devices, enabling them to be utilized in practical quantum networking applications. Finally, we develop a cavity-QED platform integrating single silicon-vacancy (SiV) centers with one-dimensional GaP-on-diamond photonic crystal (PhC) cavities. These cavities are integrated by stamp transfer and do not require any additional diamond substrate processing, enabling straightforward scalability. We then specialize PhC cavity design principles to hybrid-integrated devices, improving the PhC design metrics by nearly two orders of magnitude. We fabricate these devices and demonstrate spin-dependent scattering in the high-cooperativity regime: a requirement for cavity-QED-based devices. Altogether these results demonstrate the necessary components for realizing scalable photonic interfaces for defect qubit systems, establishing GaP-on-diamond as a promising platform for the development of quantum technologies.