CAREER: Mechanical Control of Single Spins for Sensing and Quantum Information Processing

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This CAREER project is co-funded by the Electronic and Photonic Materials Program and the Condensed Matter Physics Program.Non-technical: With advances in materials processing at the nanoscale, it is now possible to form macroscopic mechanical devices that exhibit quantum mechanical effects, behavior typically observed only in atomic-scale systems. This CAREER project builds on these advances to probe the fundamental interactions between the macroscopic motion of billions of atoms moving in unison, a phonon, and a miniscule quantum object, a single electron spin. The single spin is a nitrogen-vacancy center in diamond: a model quantum system with atom-like properties that are uniquely accessible and controllable. With its exquisite sensitivity, the nitrogen-vacancy center can be used as nanoscale quantum probe of spin-mechanical coupling; furthermore, harnessing this coupling could enable advances in quantum metrology and quantum information processing. Finally this juxtaposition of two systems existing at vastly different size scales enables fundamental explorations of macroscopic quantum mechanics and decoherence at the interface of quantum and classical worlds. This research is tightly coupled with a strong educational plan focusing on cultivating a passion for science in students of varied backgrounds by preparing them to attack the nation's challenges through innovative thinking and dedication. The Principle Investigator (PI) actively involves undergraduates, especially women and community college students, in her laboratory and establishes herself as a formal mentor throughout the years in their higher education. The PI partners with the UCSB School for Scientific Thought, in which graduate students teach Saturday classes to high-school students from diverse backgrounds, disseminating research discoveries to a wider audience. Technical: This project investigates how a single highly coherent spin and a macroscopic mechanical degree of freedom interact, what implications the interaction has for the quantum behavior of the spin, and whether spins and phonons can be functionally integrated. Single-crystal diamond cantilevers with embedded nitrogen vacancy (NV) centers are a novel platform to study spin-mechanical coupling. Motion of the cantilever generates large-amplitude strain fields with precisely controlled magnitude and direction. Single NV centers are used as quantum nanoscale sensors to measure the strain coupling coefficients and the results will guide a more complete theoretical treatment of the relevant ground-state spin interactions. Enhanced NV magnetic sensitivity is explored through strain tuning. Novel quantum sensing techniques based on spin relaxation are investigated in order to measure fluctuating fields of various origins. High quality-factor nanomechanical resonators containing NVs with long spin coherence times (about 10 ms) are formed via engineered diamond growth with nanoscale depth control of NVs. With this combination of excellent mechanical and spin properties, the quantum regime of spin-phonon coupling and phonon-mediated spin-spin interactions are explored.