Single-crystalline GaP waveguide-integrated resonators on diamond for future quantum information processing applications

Abstract

The nitrogen-vacancy (NV) defect center in diamond is considered a promising quantum bit system due its long spin coherence time, the possibility for optical manipulation and read-out and integration into solid-state photonic networks. Multi-qubit entanglement generation is essential for novel quantum information processing applications based on measurement-based quantum computing. Linear electro-optic materials such as gallium phosphide (GaP) may be crucial for the implementation of active optical device functionalities in these networks. Currently, the realization of coupled GaP photonic structures with diamond has been limited due to the lack of high-quality GaP layers on diamond. This dissertation explores different approaches toward the integration of GaP coupled optical device structures with near-surface NV centers in diamond. Initially, GaP layers grown directly on diamond using a molecular beam epitaxy system are evaluated for their optical loss properties, and found to be inadequate for the realization of high-quality GaP micro-cavity structures. Thereafter, different approaches for the transfer of single-crystalline, sub-micrometer thick GaP device layers onto diamond are investigated. Reliable transfer is achieved by an epitaxial lift-off process and subsequent van der Waals bonding of mm2-sized GaP sheets on the diamond substrate. GaP disk resonator structures integrated with bus waveguides are implemented, and their device properties are shown to be promising for the efficient collection and coupling of the relevant NV spectral line. Finally, coupling of the NV emission to a hybrid GaP\diamond optical network and on-chip photon routing is demonstrated. The work presented here is expected to open the path toward the realization of large-scale optical networks with active device functionalities, which may eventually enable high-fidelity entanglement generation between distant NV qubits in the diamond substrate.