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Nanometric quantum sensors to study 'invisible' physics

Physicists from the University of California in Santa Barbara (USA) have designed a sensor technology based on quantum mechanics, with nanometric resolution, and that operate from room temperature to the lowest temperatures, where physical phenomena are observed more hidden, and more interesting.

Using a single atom to capture high-resolution images of material at the nanoscale may sound like science fiction, but that is exactly what the Quantum Detection and Imaging Group at the University of California, Santa Barbara, has achieved.

Members of the physics lab Ania Jayich have worked for two years to develop radically new sensor technology with nanoscale spatial resolution and exquisite sensitivity. Their findings appear in the journal Nature Nanotechnology.

"This is the first tool of its kind , " says Jayich on information from the university. “It operates from room temperature to low temperatures, where a lot of the most interesting physics happens. When the thermal energy is low enough, the effects of electron interactions, for example, become observable, leading to new phases of matter. And now we can investigate them with unprecedented spatial resolution."

Under the microscope, the unique quantum sensor resembles a toothbrush. Each "bristle" contains a single solid nanofabricated diamond crystal, with a special defect, a nitrogen-vacancy (NV) center, located at the tip. It consists in that, instead of two adjacent carbon atoms, there is a nitrogen atom, which allows the detection of specific properties of materials, in particular magnetism. These sensors were manufactured in the cleanroom of the Service Nanofabrication UCSB.

The team chose to obtain an image of a relatively well-studied superconducting material that contains magnetic structures called vortices - localized regions of magnetic flux. With their instrument, the researchers were able to image individual vortices.

"Our tool is a quantum sensor because it is based on the weirdness of quantum mechanics," explains Jayich. “We put the NV defect in a quantum superposition, in which it can be in one state or another - which we do not know - and then we let the system evolve in the presence of a field and we measured it. It is this uncertainty of the overlap that allows the measurement to occur."

Such quantum behavior is often associated with low-temperature environments. However, the group's specialized quantum instrument operates at room temperature, and up to 6º Kelvin (-267º Celsius, close to 0 absolute), making it very versatile, unique and capable of studying various phases of matter and transitions. associated phase.

"A lot of other microscopy tools don't have that temperature range," explains Jayich. "Other highlights of our tool are its excellent spatial resolution, thanks to the fact that the sensor comprises a single atom. Furthermore, its size makes it non-invasive, which means it minimally affects the underlying physics in the system."

The team is currently imaging magnetic skyrmions - quasi-particles with vortex-like magnetic configurations - with immense appeal for future data storage and spintronics technologies.

Taking advantage of the nanoscale spatial resolution of his instrument, his goal is to determine the relative strength of competing interactions in matter that give rise to the skyrmions. "There are a lot of different interactions between atoms and you have to understand all of them before you can predict how the material will behave," says Jayich.

"If you get a picture of the size of the magnetic domains of the material and how they evolve on small scales of length, that gives information about the value and strength of these interactions," he adds. “In the future, this tool will help to understand the nature and strength of interactions in materials that then give rise to new interesting states and phases of matter, which are interesting from the point of view of fundamental physics, but also from that of technology. " Bibliographic reference:

Matthew Pelliccione, Alec Jenkins, Preeti Ovartchaiyapong, Christopher Reetz, Eve Emmanouilidou, Ni Ni, Ania C. Bleszynski Jayich: Scanned probe imaging of nanoscale magnetism at cryogenic temperatures with a single-spin quantum sensor . Nature Nanotechnology (2016). DOI: 10.1038 / nnano.2016.68.

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