Acoustic Control of Semiconductor Defect Spins

Acoustic control of semiconductor defect spins, a promising avenue in the realm of quantum technology. Acoustic driving, as demonstrated in this research, has the ability to manipulate the ground-state spin manifold of several defect systems with spins greater than spin-1/2. This capability holds great promise for applications in quantum information processing, where precise control over spins is essential. Furthermore, the integration of acoustic and magnetic control in hybrid systems offers an intriguing approach to transducing spin signals. Such hybrid systems bridge the gap between the quantum world and conventional technology, opening up new possibilities for seamless integration and improved functionality. Silicon carbide (SiC) is at the heart of this research for good reason. SiC has already proven itself as an ideal material platform for the development of hybrid quantum systems. It boasts a track record of success in creating high-performance optical, acoustic, and electronic devices, making it an excellent candidate for pushing the boundaries of semiconductor physics. SiC also hosts several strain-sensitive spin-active defects, making it an attractive platform for exploring the acoustic control of defect spins. This is particularly relevant in the context of microelectromechanical systems (MEMS), where SiC’s unique properties can be harnessed for advanced metrology and commercial applications.

One of the key areas where the acoustic control of defect spins in SiC shines is in the metrology of MEMS. While the metrology of diamond-based sensors has made significant strides, the utilization of defects in SiC remains a desirable advancement with far-reaching implications for commercial applications. In a new study published in the Journal Nature Electronics, a team of researchers led by Dr. Jonathan R. Dietz, Dr. Boyang Jiang, Dr. Aaron M. Day, Professor Sunil A. Bhave, and Professor Evelyn L. Hu from Purdue University discussed the acoustic control of defect spins in silicon carbide (SiC), demonstrating its potential to complement magnetic control in various applications, including sensing and quantum information processing.

Traditional techniques for analyzing the performance of MEMS resonators and filters, such as laser Doppler vibrometry and white-beam X-ray tomography, have limitations in probing the actual distribution of strain within the resonator material. This limitation hinders the optimization of resonator design, the enhancement of quality factors (Q), and power handling. Optically detected spin-acoustic resonance (ODSAR)-based MEMS characterization emerges as a promising solution. This depth-sensitive, room-temperature metrology approach offers insights into the spatial distribution of strain within MEMS resonators, enabling more precise optimization and performance enhancement.

A critical aspect of this research revolves around silicon monovacancies in SiC, which have long been studied as a spin-photon interface. Specifically, the study focuses on the singly negatively charged k-site silicon monovacancy (VSi−), which exhibits a bright, near-infrared optical transition and a spin-3/2 ground-state manifold. This defect system is particularly attractive due to its suitability for room-temperature ODSAR.

Monitoring VSi− within acoustic resonators is a key objective of the research, and this poses unique challenges and opportunities. Acoustic resonators, particularly bulk acoustic resonators, offer the advantage of storing mechanical strain energy in the bulk material rather than solely in the piezoelectric transducer. This characteristic enables the development of devices with locally addressable emitters in the bulk material, a significant advancement in the field.

Bulk acoustic resonators play a pivotal role in this research. Specifically, the study reports the acoustically mediated spin control of naturally occurring silicon monovacancies (VSi−) in high-Q lateral overtone bulk acoustic resonators (LOBARs) fabricated in high-purity semi-insulating 4H-SiC. LOBARs, designed to preserve strain throughout the entire resonator body rather than just the surface, have demonstrated impressive mechanical Q values ranging from 3,000 to 20,000 across a wide range of frequencies.

The new study scrutinizes the spatial characteristics of the acoustic coupling of LOBARs to an ensemble of silicon monovacancies. It demonstrates spatial, directional, and frequency strain sensitivity, showcasing the capability of LOBARs in achieving coherent acoustic control of silicon monovacancies within SiC. The authors measured ODSAR in LOBAR devices. VSi−, being a naturally occurring intrinsic point defect in these devices, provides a unique opportunity to study the coupling between its acoustic mode and its ground-state spin. To unequivocally establish the spin-acoustic coupling, the researchers employ a differential approach. They alternately apply strain to the ensemble using a differentially driven acoustic resonance via interdigital electrodes and magnetic driving via a nearby suspended RF antenna. This approach allows them to explore the intricate interaction between strain and spin in the VSi− system.

The authors introduced a spin–strain coupling Hamiltonian, emphasizing the critical role of strain-coupling tensors, Cartesian strain, and spin matrices in driving the spin-3/2 defects. The orientation of the magnetic field plays a pivotal role in manipulating the spin resonances, with a focus on Δms = ±1 and Δms = ±2 transitions. The measurement process involves the collection of differential fluorescence from the k-site VSi− over a specific wavelength range. This data enables the researchers to quantify the ODSAR and delve into the intricacies of spin-acoustic resonance in SiC.

It is noteworthy to mention that the authors reported the ability to perform high-spatial-resolution mapping of strain inside MEMS resonators. Traditional metrology techniques often fall short in providing in-depth insights into the distribution of strain within the resonator material. The advent of ODSAR-based MEMS characterization offers a compelling solution, enabling engineers and scientists to optimize resonator design, enhance quality factors (Q), and improve power handling with a more profound understanding of strain distribution. Two primary mode families, namely the low-frequency flexural (A0) and high-frequency extensional (S0) modes, come into focus. These modes exhibit distinct strain characteristics, with flexural modes featuring out-of-phase longitudinal strain modes and extensional modes displaying in-phase longitudinal strain. Understanding the nuances of these modes is essential for harnessing their potential in quantum technologies. In conclusion the new study narrows its focus on Δms = ±1 transitions due to their relevance in coupling both shear and longitudinal strain. The data obtained through these experiments offers valuable insights into the relationship between spin resonance intensity and