Mechanically Mediated Spin Entanglement in Diamond

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Diamonds consist of a regular arrangement, or lattice, of carbon atoms, which often contains defects at the atomic level. Common defects include impurities, such as nitrogen or silicon atoms, and vacancies - places in the lattice where atoms are missing. A special defect is a “silicon-vacancy” center, which consists of two vacancies that are adjacent to each other, with a silicon atom inserted in between. An electron can be trapped around such a defect, and used as a “qubit,” or “quantum bit”—a fundamental unit of quantum information. An outstanding challenge for using these qubits to develop solid-state quantum computers is the precise control of the interactions between them. This program will develop an experimental approach that uses mechanical vibrations in an ultrathin diamond film to mediate interactions between two silicon-vacancy qubits. Mechanical waves can be conveniently confined and guided in a suitably designed solid-state nanostructure with negligible loss, opening up a new frontier in the development of quantum information technologies. In addition, this program will also make contributions to education and human resources by providing excellent training to graduate and undergraduate students in areas of both scientific and technological importance.This experimental program focuses on mechanically mediated coupling between electron spins in a diamond nanomechanical resonator, with the long-term goal of establishing a trapped-ion-like solid-state platform for quantum computing. The primary building block of this platform is a diamond Lamb wave mechanical resonator, in which electron spins in silicon vacancy centers couple to a symmetric mechanical compression mode. The Lamb wave resonator is protected by a phononic crystal lattice, which can enable the achievement of mechanical Q-factors limited only by the intrinsic material loss of diamond. Two mechanisms that take advantage of the special energy level structure of silicon vacancy centers will be explored for the coupling between spins and mechanical vibrations. One exploits optically driven sideband spin transitions. The other uses mechanical vibrations to directly drive spin transitions. The sideband spin transitions will be used for spin entanglement through a Molmer-Sorensen two-qubit gate, which is widely used for trapped ions. The direct acoustic driving will be used for spin entanglement via a phononic cavity QED process.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.