Researchers from the Technical University of Munich and MCQST have demonstrated a new class of quantum sensors based on spin defects hosted in boron nitride nanotubes (BNNTs), representing an important step toward chemical and magnetic sensing at room temperature. By exploiting the unique geometry of BNNTs together with the optical and spin properties of their defects, the team established a high-surface-area quantum sensing platform suitable for operation in liquid environments. The results have been published in Nature Communications.

Optically active spin defects in solid-state materials are atomic-scale imperfections that host electronic spins acting as localized and controllable qubits, while simultaneously providing a convenient spin photon interface that enables optical readout of the spin state. These systems have emerged as a promising platform for quantum sensing operating at room temperature, and nitrogen vacancy centers in diamond have long served as a benchmark system.

Extending spin-based quantum sensing to alternative material platforms is essential to enable new sensing geometries, improved analyte access, and scalable architectures.

In recent years, van der Waals materials such as hexagonal boron nitride have attracted growing attention as hosts for optically active spin defects. However, planar two-dimensional systems inherently limit surface accessibility and interaction volume, thereby constraining their applicability in chemical and biological environments.

A nanotube-based quantum sensing platform

In the new study, the research team led by Dr. Roberto Rizzato, in the Quantum Sensing Group of Prof. Dominik Bucher at TUM, introduces boron nitride nanotubes as a fundamentally different quantum sensing architecture. BNNTs combine the favorable optical and spin properties of boron nitride with a hollow cylindrical geometry that provides a large and accessible surface area. Crucially, the spin defects in BNNTs exhibit an isotropic spin-½ magnetic response, enabling quantum control independent of the nanotube's orientation with respect to an external magnetic field. This enables the use of randomly oriented nanotube ensembles, forming mesh-like sensor structures that are well suited for interaction with liquids and complex chemical environments.

Extending coherence and enabling sensing

To unlock the sensing potential of these spin defects, the team applied advanced spin-control techniques, including dynamical decoupling sequences, to extend the spin coherence times by more than two orders of magnitude and to enable the detection of radiofrequency signals with high spectral resolution. In addition, the researchers demonstrated sensitive detection of paramagnetic ions in solution at micromolar concentrations, achieving levels of detection nearly three orders of magnitude better than in previously reported boron nitride platforms.

Outlook and future applications

Spin defects in boron nitride nanotubes enable applications that are difficult to realize with existing solid-state quantum sensors. BNNTs could serve as nanoscale quantum sensors in liquids, or dynamic and disordered environments, with relevance for chemistry, biology, and energy technologies. They can combine quantum sensing with nanofluidic and nanopore technologies. At larger scales, BNNT mesh sensors may enable real-time monitoring of contaminants in water. Finally, their large accessible surface area makes BNNTs promising candidates for room-temperature nuclear spin hyperpolarization, opening a path toward compact and scalable quantum-enhanced NMR technologies. Dr. Roberto Rizzato recently received an ERC Consolidator Grant to further develop this technology for hyperpolarization and nanoscale magnetic resonance.

Publication

R.Rizzato, A. A. Hidalgo, L. Nie, E. Blundo, N.R. von Grafenstein, J. J. Finley & D.B. Bucher. Quantum sensing with spin defects in boron nitride nanotubes. Nature Communications.
DOI: 10.1038/s41467-025-67538-2

Original article: https://www.mcqst.de/news-and-events/news/spin-based-quantum-technology-in-a-1d-material.html