EAGER: Enabling Quantum Leap: Electrically tunable, long-distance coherent coupling between room temperature qubits mediated by magnons in low-dimensional magnets

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Nontechnical description: The counterintuitive laws of quantum mechanics (not observable in a classical world) offer the possibility to build next generation of information processing, communication and sensing technologies capable of far outperforming present-day devices. Quantum phenomena are extremely susceptible to interactions with the environment and are generally limited to ultralow temperatures, where interactions are minimal. In stark contrast, atomic-scale defects in diamond, being sufficiently isolated from the environment, exhibit quantum properties even at ambient conditions. Consequently, such systems are ideal building blocks for creating room temperature quantum devices. However, in order to realize scalable room temperature quantum devices, it is imperative to increase the range of interaction between individual defects, while also having the control to turn the interaction on and off. This project addresses these outstanding challenges by developing a novel hybrid material platform of diamond defects interfaced with thin magnetic films, where the required long-distance and controllable quantum interaction between individual defects is mediated magnetically. The project also aims to enhance the United States' quantum engineering workforce by providing interdisciplinary training to undergraduate and graduate students at the interface of quantum physics, engineering and materials science. Technical description: Nitrogen vacancy centers in diamond have emerged as the dominant room temperature quantum bit for building quantum technologies. However, scaling coherent coupling beyond Nitrogen Vacancy centers separated by few tens of nanometers has proven challenging. This research project aims to provide a solution to this materials challenge by demonstrating electrically tunable coherent coupling between Nitrogen vacancy qubit spins at room temperature, which are separated by near micrometer distances. For this purpose, a novel platform is proposed, where the coherent coupling between Nitrogen vacancy centers is mediated by magnons confined in electrically controlled low-dimensional magnets. The proposed platform takes advantage of two recent experimental advances, namely: (a) strong resonant enhancement of magnon-Nitrogen vacancy spin coupling, and (b) enhanced electric-field tunability of low-dimensional magnets. The resonant enhancement, in combination with the long-distance transport of magnons, allows for the possibility of mediating long range coherent coupling; while the electrical tunability of these resonances offers exciting possibility to turn the coherent coupling on and off. In particular, the project takes advantage of these previously unavailable opportunities to extend the range of coherent coupling beyond the state-of-the-art demonstrations for room temperature quantum bits, as well as, demonstrate an on-demand quantum gate functionality. The proposed research provides opportunities for technological applications, while it also offers unique educational opportunities for training the next generation of quantum technologists and scientists. Specifically, successful completion of the project provides the missing link towards building a scalable platform for quantum technologies working at ambient conditions. On the other hand, the intersection of quantum information processing and spintronics also offers new opportunities for interdisciplinary training of students and postdocs, development of new courses, and outreach to the public. For this purpose, the team proposes to leverage existing undergraduate research experience programs at Purdue, along with posting of online seminars on nanoHub (the largest online resource of nanotechnology) for dissemination to a broader community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.