Quantum Spin-Mechanics with Color Centers in Diamond

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

Diamond consists of a regular array or a lattice of carbon atoms as well as an extremely small number of defects in the carbon lattice, including impurities, such as nitrogen or silicon atoms, and vacancies - places in the lattice where atoms are missing. Suitable combinations of impurities and vacancies can lead to the formation of color centers, which interact with light and give color to an otherwise transparent diamond. A special color center is a “silicon-vacancy”, which consists of two adjacent vacancies with a silicon atom inserted in between. An electron trapped in such a color center can serve as a “quantum bit” or a qubit - fundamental unit of quantum information. An outstanding challenge for using these qubits to develop solid-state quantum computers is to mediate and precisely control the interactions between the qubits. This experimental program couples silicon vacancy qubits to the compressional mechanical vibrations of a micrometer-sized thin rectangular diamond plate, which is embedded in a specially designed square lattice fabricated on the diamond film. The vibrational energy level structure of the square lattice isolates and protects the compressional vibrations. Interactions between the qubit and the compressional vibrations will be investigated at the level of single quanta of the mechanical vibrations, with the goal of mediating and controlling interactions between two silicon-vacancy qubits through their coupling to the mechanical vibrations. In addition, this program will also make contributions to education and human resources by providing excellent training to graduate and undergraduate students in quantum information science and technology. This program focuses on experimental studies of diamond spin-mechanical systems, in which spin qubits are coupled to vibrations of a nanomechanical resonator. The primary experimental platform is a GHz diamond Lamb wave resonator, essentially a thin rectangular elastic plate with free boundaries, embedded in a phononic crystal lattice. Owing to the protection by the suitably designed phononic band gap, the compressional mechanical modes of the Lamb wave resonator can feature ultrasmall mechanical loss with a mechanical linewidth less than a few hundred Hz. Spin qubits such as silicon vacancy centers will be implanted in diamond Lamb wave resonators. These resonators will be employed for the exploration of the quantum regime of spin-mechanics through a phononic cavity QED process, for which a silicon vacancy spin qubit is coupled to the fundamental compression mode via a direct acoustic transition. The ultrasmall mechanical loss and the robust spin coherence of a silicon vacancy spin qubit at low temperature can in principle lead to cooperativity, a dimensionless parameter that characterizes the spin-mechanical coupling, as large as 1 million. The successful completion of these studies will pave the way for entangling two distant spin qubits via their coupling to a mechanical normal mode of coupled mechanical resonators. 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.