Researchers create direction-independent magnetic field-sensing nanotube spin qubits

Researchers at Purdue University have developed patent-pending one-dimensional boron nitride nanotubes (BNNTs) containing spin qubits, or spin defects. BNNTs are more sensitive in detecting off-axis magnetic fields with high resolution than traditional diamond tips used in scanning probe magnetic field microscopy.

Professor Tongcang Li is a professor of physics and of electrical and computer engineering and leads the team that developed BNNTs with optically active spin qubits. He is also a faculty member at the Purdue Institute for Quantum Science and Engineering. The team includes Purdue graduate students Xingyu Gao, Sumukh Vaidya, and Saakshi Dikshit, who are co-authors of the paper published in Nature Communications.

“BNNT spin qubits are more sensitive to detecting off-axis magnetic fields than diamond nitrogen vacancy centers, which are primarily sensitive to magnetic fields parallel but not perpendicular to their axis,” Li said. “BNNTs are also cost-effective and have higher elasticity than brittle diamond chips.”

BNNT applications include quantum sensing technologies that measure changes in magnetic fields and collect and analyze data at the atomic level.

“It also has applications in the semiconductor industry and nanoscale MRI, or magnetic resonance imaging,” Gao said.

BNNT spin qubit testing and development

The system was tested in a custom-built laboratory system that includes a laser, detector, and signal generator to control the quantum state of the nanotube spin qubit.

“These BNNT spin qubits are sensitive to magnetic fields and exhibit magnetic resonances that are detected optically,” Vaidya said. “When exposed to a magnetic field, the energy level of the spin qubits within the BNNTs changes, which can be measured using light.”

In initial demonstrations, BNNTs performed as well as diamond chips.

“Boron nitride nanotubes are spatially much smaller than diamond tips, so we expect to achieve superior numbers with this system,” Dixit said.

Li said the Purdue researchers aim to improve the spatial resolution and magnetic field sensitivity of the BNNT spin qubit system. These improvements could enable quantum sensing of phenomena at the atomic scale.

“This will enable very high-resolution scans of surface magnetic properties,” Vaidya said. “Improving sensitivity allows us to obtain more accurate information or achieve faster readout of external magnetic fields, both of which have applications in quantum science, memory storage, medicine, and the semiconductor industry. ”