Exploring Carrier Spin Injection, Transport, and Trapping in Diamond

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Methods to control interactions between individual atoms in solid state crystals are important for next generation technologies that will encode information in atomic spins. This project will pioneer a new approach for manipulating one atom's spin conditionally on the quantum mechanical spin of another. Individual atoms such as point defects in a diamond crystal lattice where a nitrogen atom is substituted for a carbon atom, known as NV centers, will be used. Individual NV centers will be controlled with optical and electronic pulses so they can send spin-dependent signals to each other. NV centers in diamond are already known to be valuable resources for storing and processing quantum information locally. But there are still fundamental questions about how to build a network that can shuttle quantum information back and forth between several NV centers. This project addresses that challenge by using laser light and electric fields to create a spin-dependent motion of an electric charge from one NV center to another NV center. The understanding to be gained from this effort will help with the effort to build components for new and more powerful types of computers called quantum computers. Furthermore, the approach used here will pioneer quantum computer components that use solid state devices operating at room temperature to process quantum information. Besides the technological and scientific advantages, the proposed research is expected to have a broad educational outcome because it offers students a unique inter-disciplinary scientific education and the ability to interact with a wide network of collaborating labs. These activities gain special meaning at City College, a minority serving institution with a uniquely diverse population of inner-city students. This research program explores the use of photo-generated charge carriers as a bus to communicate between separate, non-interacting NVs within a diamond crystal or nano-structure. Diamond is arguably an ideal platform for quantum spintronics because it has inversion symmetry, contains a low concentration of spin-active nuclei, and features one of the weakest spin-orbit couplings. However, virtually no investigation of the carrier spin dynamics in diamond has yet been carried out, because injection and detection of spin polarized carriers through known strategies (e.g., optical excitation or ferromagnetic interfaces) has proven difficult. This project circumvents prior complications via a flexible scheme where NV centers alternatively serve as a source or a probe of carrier spin polarization. Building on prior observations the initial goal is to gain a fuller understanding of the physics governing the dynamics of charge carriers, including photo-ionization, diffusion, and carrier trapping. With focus on the NV center and substitutional nitrogen centers, the research plan encompasses a broad set of experiments designed to explore deterministic injection, transport, and capture of spin-polarized carriers. Special attention will be devoted to the problem of coherent spin transport, particularly in its ability to generate entanglement between qubits not interacting directly. While the emphasis is on the phenomenology and physics, the research plan also calls for various proof-of-concept devices conceived to gain adequate control of the dynamics.