Nanophotonic integration and engineering of defect qubits in diamond

Abstract

Solid-state defect qubits are emerging as a promising candidate for quantum information processing. A fundamental resource for quantum information is entanglement between distant qubit nodes. Several quantum platforms have demonstrated entanglement generation between two physically separated qubits. However, a scalable platform to efficiently entangle multiple qubits remains elusive. Optically addressable defect qubits in diamond such as the nitrogen-vacancy (NV) and the silicon-vacancy (SiV) centers serve as the foundation of this thesis. The crucial components of optically interfaced defect qubit platforms are high-fidelity initialization, manipulation and readout of the qubit spin state accomplished using photoluminescence on an optical cycling transition. Here, we demonstrate significant steps towards realizing these components with a gallium phosphide (GaP) on diamond hybrid photonic platform. Utilizing individual defect qubits created by targeted defect formation process, experimental results on various defect-photonic coupling geometries are presented. Enhanced photon collection efficiency is measured for implanted NV centers coupled to disk-resonators and inverse-designed photon extraction devices. One of the main challenges encountered with coupled NV devices is the significant spectral instability. By performing large-scale automated resonant spectroscopy on the implanted NV centers, we determine that defect-surface interaction are the dominant source of the observed spectral instability. This leads us to consider the SiV center in diamond, which exhibits inherent protection from electric field fluctuations arising by its inversion symmetry within the diamond lattice. We demonstrate coupling of SiV centers to 1-D photonic crystal cavities (PhC) fabricated in GaP. To avoid perturbation of the diamond surface, we fabricate the PhCs on a separate chip and integrate with SiV centers in diamond by a stamp-transfer technique. Ancillary components for a single chip architecture such as single photon detectors, coherent frequency-conversion and passive photonics utilizing GaP are also demonstrated. These results establish GaP-on-diamond as a suitable platform for efficiently interfacing defects qubits with nanophotonic devices for scalable entanglement generation.