CQIS: Coherent Spin-Phonon Interfaces with Diamond Color Centers

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Part 1: Quantum science and technology promise the realization of powerful computers and a secure internet, which together could lead to the development of unprecedented distributed quantum computational resources. To achieve this goal, the development of systems comprising many coupled quantum bits (qubits) with the ability to perform storage, communication and multi-qubit logic operations is essential. Atomic-scale luminescent defects - color centers - in diamond have recently emerged as a leading solid-state platform that has many of these characteristics. However, approaches to efficiently couple different color centers using light have been limited by a photon loss. This is largely due to the difficulties associated with confining light to a sub-micron volume on a diamond chip. The proposed program will explore an alternative approach to qubit coupling that relies on mechanical vibrations, and will thus enable a new generation of capabilities for the field of quantum science and technology, with applications in quantum information processing and quantum metrology. The program addresses topics related to quantum engineering, quantum information science, nanofabrication, material science, nanophotonics and nanomechanics and has strong theoretical and experimental component. Therefore, it represents a unique research and educational opportunity for students at all levels. Part 2: Atomic-scale luminescent defects in diamond have recently emerged as a leading solid-state platform for realization of on-chip quantum networks. Of particular importance are negatively charged nitrogen-vacancy (NV) and silicon-vacancy (SiV) color centers that possess all the essential elements for quantum technology: storage, control and read-out. While the NV remains the best solid state quantum memory, recent work has shown that SiV is superior quantum emitter with spectrally stable and atomic-like emission. Furthermore, it has been demonstrated that SiV properties can be engineered by applying strain, induced by mechanical motion. In this program, strong spin-strain coupling in SiV will be leveraged to realize quantum networks that utilize acoustic phonons as information carriers in on-chip quantum networks. For example, by embedding SiVs inside phononic cavities and waveguides, it will be possible to engineer spin-phonon interactions and achieve controlled phonon emission and absorption by SiVs, as well as phonon routing, storage, and phonon-phonon interactions (phonon switches). This will enable realization of two-qubit quantum gates based on SiVs embedded inside mechanical resonators, in which qubit entanglement is mediated by mechanical vibration. On the other hand, by surrounding SiV with a phononic bandgap structures, phonon emission process will be suppressed thus enhancing the SiV spin coherence time by several orders of magnitude. The proposed program will pave the way for a new field of quantum acousto dyanmics that uses phonons, and mechanical vibration in general, as on-chip information carriers. Importantly, since mechanical vibrations can be engineered to couple coherently to many different qubits (spin, charge, flux, photon), proposed efforts may enable transfer of quantum states between different degrees of freedom, and lead to realization of hybrid quantum networks.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.