Researchers at the University of Tokyo have successfully organized quantum sensors on a nanoscale, enabling them to detect extremely minute variations in magnetic fields. The study of quantum materials and electronic devices may benefit from high-resolution quantum sensors. For instance, the sensors may be of assistance in the creation of hard disks that make use of nano-magnetic materials as storage components. Using a nanoscale arrangement of quantum sensors, this is the first successful high-resolution magnetic field imaging in history.
We are constantly surrounded by sensors, including atoms, smoke detectors, and garage lights. Using the characteristics of an atom, quantum sensors are able to detect the environment around them. In response to a magnetic field, for instance, an atom alters its spin, which has two values similar to the poles of a magnet. There are numerous applications for magnetic field sensors in quantum materials research and biomedical appliances, including superconductors.
“Using such an unprecedented sensor, we want to observe a microscopic world that no one has ever seen,” asserts Assistant Professor Kento Sasaki at the University of Tokyo.
“Although individual quantum sensors are small, the spatial resolution of the sensor is limited by the distance between the sensor and the measurement target,”
Kento Sasaki, an Assistant Professor at the University of Tokyo,
Stable quantum sensors for targets like wires and disks were the goal of the researchers. However, it has been difficult to precisely arrange atoms in order to sense even the smallest changes in the magnetic field up until this point.
According to Sasaki, “even though individual quantum sensors are small, their spatial resolution is limited by the distance between the sensor and the measurement target.” The researchers devised a method for fabricating nanoscale quantum sensors on the surface of the measurement target in order to resolve the issue.
As quantum sensors, the group utilized boron openings or cross-section surrenders in the two-layered hexagonal boron nitride, a slender glasslike material with nitrogen and boron iotas. Since its discovery in 2020 as a quantum spin sensor, the boron vacancy defect has emerged as the new kid on the block.
The team was able to remove a thin film made of hexagonal boron nitride from the crystal by removing the Scotch tape. The researchers adhered the thin film to the gold wire that was the target. After that, a high-speed helium ion beam was used to bombard the film, ejecting boron atoms and creating 100 nm2 of boron vacancy spots.
Each spot has a lot of vacancies the size of atoms that act like tiny magnetic needles. The sensors have better spatial resolution the closer the spots are to one another. Based on the intensity of light emitted from the spots when microwaves were present, the team measured the magnetic field at each spot as current passed through the wire. When the measured magnetic field values closely matched the simulated values, the researchers were amazed, demonstrating the effectiveness of the high-resolution quantum sensors.
The sensor’s spin state can be detected even at room temperature in the presence of a magnetic field, making it simple to identify the local magnetic field and currents. Additionally, the quantum sensors easily adhere to various materials due to the van der Waals force by which the boron nitride nanofilms attach to objects.
The researchers were able to construct a thin layer that could be attached to a target gold wire thanks to this.Credit: Sasaki et al., 2023.
Sasaki and his team intend to use this method in studies of quantum materials and condensed matter physics. “It will empower direct discovery of the attractive field from, for instance, unconventional states at the edges of graphene and minute quantum spots,” adds Sasaki.
Quantum sensors the size of atoms are beginning to change how we perceive microscopic environments and comprehend their macroscopic properties. They can be used for more than just basic science research. They are capable of assisting in the imaging of human brains, pinpointing precise locations, mapping underground environments, and detecting tectonic shifts and volcanic eruptions. The potential applications of their nanoscale quantum sensors in superconductors, magnetic materials, and semiconductors are awaited by Sasaki and his team.
The research has been published in the Applied Physics Letters journal.
More information: Kento Sasaki et al, Magnetic field imaging by hBN quantum sensor nanoarray, Applied Physics Letters (2023). DOI: 10.1063/5.0147072
