Engineering and quantum control of single spins in semiconductors

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troduction The past two decades have seen extensive research aiming to understand the extent to which the electron’s spin degree of freedom can be controlled to add functionality to conventional semiconductor devices. 1 A central effort in this fi eld of “semiconductor spintronics” has been to identify single spin systems that can be measured and manipulated, inspired by the potential use of single spins as elementary units of quantum technologies that perform tasks inaccessible to classical electronics. Indeed, many groundbreaking experiments demonstrated that such single spin control is possible in solidstate systems such as quantum dots, donors in silicon, and defect spins in diamond.2 In turn, these demonstrations have led to new challenges: developing applications that benefit from the quantum nature of single spins and engineering large-scale systems in which both single spins and their mutual interactions can be controlled for quantum information processing. A paramagnetic impurity in diamond known as the nitrogenvacancy (NV) center has gained increasing attention because its remarkable properties make it a promising candidate for addressing these challenges. The NV center combines long-lived spin coherence, optical spin initialization and measurement, and proximal coupling to individual nuclear spins, enabling the execution of quantum algorithms on coupled spin systems

(see the Introductory and Childress and Hanson articles in this issue). Moreover, the ability to perform these operations at room temperature or higher3 presents the intriguing prospect of utilizing these spins to sense weak electromagnetic fields on nanometer length scales in ambient conditions (see the articles by Hong et al. and Hall et al. in this issue). However, realizing the NV center’s potential requires engineering increasingly sophisticated devices in diamond that integrate technologies from fields such as microwave electronics, photonics, single dopant fabrication, and materials synthesis. We review recent advances in this area, in particular focusing on interfacing NV centers with solid-state electronic devices that enable highfidelity control over the defect’s quantum degrees of freedom, the controllable fabrication of single defects on technologically relevant length scales, and recently discovered defects in technologically mature materials that enable functionalities beyond those accessible to the diamond NV center.

Interfacing NV centers with solid-state electronics A primary motivation for pursuing quantum technologies based on solid-state platforms is their inherent flexibility with regard to engineering scalable device geometries. Photolithographic patterning of metal electrodes on diamond surfaces has enabled

David M. Toyli, Center for Spintronics and Quantum Computation, University of California, Santa Barbara; [email protected] Lee C. Bassett, Center for Spintronics and Quantum Computation, University of California, Santa Barbara; [email protected] Bob B. Buckley, Center for Spintronics and Quantum Computation,