24 November 2023
Spin-based quantum technology in a 2D material
Researchers from the Technical University of Munich, the Walter Schottky Institute, and the Helmholtz-Zentrum Dresden-Rossendorf achieved a significant milestone by utilizing spin defects as optically active quantum bits (qubits) within hexagonal boron nitride (hBN), a well-known 2D material. The team extended the room-temperature coherence time of Boron-Vacancy (VB-) centers in hBN by two orders of magnitude, showcasing their potential as quantum sensors for radiofrequency signals. This breakthrough not only initiates spin sensing techniques for studying 2D materials and their heterostructures but also positions these systems as key contributors to the development of room-temperature ultra-miniaturized devices, driving advancements in quantum technology and spintronics. The results have been published in Nature Communications.
While extensive research has been conducted on NV centers in diamond, the exploration of optically active spin qubits within alternative solid-state lattices has been comparatively limited, despite the immense untapped potential this avenue offers for future quantum technologies.
In recent developments, defect centers within van-der-Waals materials, such as hexagonal boron nitride (hBN), have been both experimentally identified and theoretically examined. Notably, negatively-charged Boron Vacancy (VB-) centers in hBN have shown their promise as sensors for temperature, pressure, and magnetic fields, unlocking possibilities for ultra-miniaturized measurement devices. Nonetheless, their limited spin coherence time has posed a significant challenge in practical quantum technology applications.
Pioneering precision harnessing spin defects in hBN for future quantum technologies
The research team, led by Dr. Roberto Rizzato of the TUM Quantum Sensing Group of Prof. Dr. Dominik Bucher, tackled this challenge by employing spin control techniques known as dynamical decoupling to effectively isolate the spin defects from the environmental magnetic noise, thereby substantially extending their coherence time by two orders of magnitude. This breakthrough allowed the team to demonstrate advanced qubit control, enabling the implementation of quantum sensing protocols and showcasing their ability to detect radiofrequency signals with high spectral resolution and sensitivity. These results demonstrated the potential of the VB- in hBN as quantum sensors, similar to the well-established NV-centers in diamond.
However, hexagonal boron nitride (hBN) systems distinguish themselves from diamond as they consist of micrometer-sized ultra-thin flakes, with thickness ranging from nanometers to the ultimate monolayer limit. In their research, the team exfoliated these flakes from seed crystals and utilized helium ion implantation at the ion beam facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) to generate spin defects. Subsequently, they transferred the flakes onto a sapphire substrate equipped with gold microstriplines, enabling precise delivery of high-power microwaves (MW) for finely-tuned spin manipulation. As part of their work, the team engineered a specialized microscope tailored for spatially resolved Optically Detected Magnetic Resonance (ODMR) measurements, enabling examination and control of VB- spin ensembles within specific areas of the sample.
The implications of this research span various fields. In materials science, spin defects in hBN can find applications in nanoscale sensing, providing insights into the structure and properties of thin materials and 2D heterostructures across a broad range of experimental conditions. In chemistry, these defects may contribute to understanding catalytic processes within hBN at the nanoscale. In biomedicine, they could serve as wearable magnetometers for medical diagnostics and point-of-care technologies. In quantum simulation and communication, the intriguing nuclear spin networks surrounding the defects hold potential for enabling the arbitrary preparation of nuclear spin states and the realization of electro-nuclear spin entanglement.
Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing.
R. Rizzato, M. Schalk, S. Mohr, J. C. Hermann, J. P. Leibold, F. Bruckmaier, G. Salvitti, C. Qian, P. Ji, G. V. Astakhov, U. Kentsch, M. Helm, A. V. Stier, J. J. Finley and D. B. Bucher.
Nature Communications volume 14, Article number: 5089 (2023)
Roberto Rizzato & Dominik Bucher
Quantum Sensing Group
Technical University of Munich (TUM)
Department of Physical Chemistry
85748 Garching b. München
Emails: roberto.rizzato[at]tum.de, dominik.bucher[at]tum.de