Scientists from the Institute of Physics of Kazan Federal University (KFU), together with staff from the A.F. Ioffe Institute of Physics and Technology of the Russian Academy of Sciences and the A.M. Prokhorov Institute of General Physics of the Russian Academy of Sciences, participated in an international study dedicated to expanding understanding of the spin interactions of a VB defect with remote nuclear magnetic moments.
The research belongs to the rapidly developing field of quantum technologies, which are based on optically polarizable spin states of defects in solid-state crystals. These defects behave like isolated atoms and can be used as quantum bits (qubits). They can be used to create highly sensitive quantum sensors, computing devices, and quantum communication systems.
Previously, the main attention in this field was focused on three-dimensional crystals such as diamond or silicon carbide, where spin centers, in particular nitrogen vacancy (NV), demonstrated outstanding properties: long coherence time, optical readability, and high sensitivity to external fields. However, in recent years, two—dimensional materials have come to the fore, the uniqueness of which lies in the fact that the atoms in them are bound by strong covalent bonds, while the layers themselves are bound by weak Van der Waals forces.
"By breaking this weak interaction, it is possible to obtain materials that are the ultimate condensed state of matter — a two-dimensional layer one atom thick. One of the most promising representatives of this group is hexagonal boron nitride (hBN), also called "white graphene" due to its crystallographic similarity to classical graphene," said Fadis Murzakhanov, one of the study participants and a researcher at the Advanced Platforms for Spin Quantum Manipulation Research Institute of the KFU Institute of Physics.
According to the scientist, a unique opportunity for quantum technologies turned out to be the discovery of such a defect in this material as a negatively charged boron vacancy (VB-) — a missing boron atom in the two-dimensional plane of hybridized nitrogen and boron atoms.
"This defect has a triplet electronic spin state, demonstrates a record high degree of optically induced spin polarization close to 100 percent at room temperature, and outstanding spin coherence times of a polarized spin system in the range of tens of microseconds. These properties of the VB-defect—based qubit formed the basis for the development of nanoscale quantum sensors for magnetic fields, temperature, pressure and other physical parameters," said Fadis Murzakhanov.
The aim of the work was to expand the understanding of the spin interactions of the VB defect with remote nuclear magnetic moments. The scientists demonstrated the possibility of detecting and spectroscopically analyzing nuclear spins located at a considerable distance from the center of the defect, and characterized the nature of their interactions with the electron spin of the vacancy. The study was carried out using a complex of modern methods, including photoinduced pulsed spectroscopy of electron paramagnetic resonance and double electron-nuclear resonance in the high-frequency range of the installation (94 GHz), supplemented by quantum chemical calculations within the framework of the density functional theory.
"For the first time for the VB-defect: Nuclear Lattice Spins hBN system, we were able to demonstrate the registration of long-range magnetic moments of atoms by measuring nuclear magnetic resonance signals. To identify these magnetic moments as distant nuclear spins of nitrogen atoms located approximately 0.4 nanometers away from the boron vacancy in a two-dimensional layer of hexagonal boron nitride. The analysis of the orientation dependence of the spectra made it possible to accurately localize these atoms in the third coordination shell and quantify their hyperfine and quadrupole interactions with the electron spin of the defect," shared the results of the laboratory design engineer who also participated in the study. ekaterina dmitrieva.
The authors note that the results obtained lay the foundation for the creation of various next—generation quantum devices, from miniature sensors capable of detecting single centers/spins to complex computing platforms and spin-photon interfaces, which will find their application in biomedical diagnostics, research of new materials and the development of quantum computers. In addition, the work done provides an understanding of long-range spin interactions in atomically thin systems, which is important from a fundamental and practical point of view.
The work was carried out with the support of the Russian Science Foundation.
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