Quantum Engineering of a Diamond Spin Qubit With Nanoelectromechanical Systems

Abstract

Quantum emitters are indispensable building blocks for quantum computers and networks. By entangling multiple individual quantum systems, it is possible to make overall system exponentially more powerful. Quantum emitters play a key role in this regard, since they offer an optical interface between a flying qubit (photon) and a stationary qubit (spin) for a long distance. Among those, solid-state emitters are an appealing candidate for its scalability. Among many kinds, we study color centers in diamond: nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers. Being trapped atom in a solid, a color center provides both unique opportunities and challenges. Using dynamic interaction between phonons and spin qubits, it is possible to build an on-chip universal quantum bus. On the other hand, the host material causes inhomogeneous distribution of emitters by its material strain and exposes color centers to thermal lattice vibrations. In this work, we use nanoelectromechanical systems (NEMS) to address both issues. First, we make nanocantilevers with embedded NV centers and use its flexural motion for parametric coupling. Both electron spin resonance and spin-echo measurements are performed. As a result, we deduce the single-phonon coupling rate of approximately 1.8 Hz, which is still many orders of magnitude smaller than the minimum requirement for a quantum node. Therefore, it is necessary to further scale down the device without deteriorating other parameters. In this context, we fabricate on-chip dynamic actuator that is compatible with cantilevers of small mode volume and high quality factor. We measure resonant frequencies of fundamental flexural modes on the order of tens of MHz, with mechanical quality factors on the order of thousands. Finally, we present electrostatically actuated diamond cantilever with implanted SiV centers. By deflecting beams, we control the electronic structure of SiV centers, which is revealed by taking optical spectra at different strain conditions. Furthermore, we probe the dynamics of the spin qubit while controlling strain. By applying strain on the order of ten-thousandths to SiV centers, we improve the spin coherence time by sixfold at 4K, until it is limited by a next dominant dephasing mechanism. We conclude with an outlook of phononic quantum nodes with SiV center.