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The quantum measurement method measures minuscule magnetic fields

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A new method of measuring magnetic fields with magnetic atomic waves with great precision, not only up and down but also laterally, has been developed by researchers at MIT. The new tool can be useful in applications that are as diverse as mapping the electrical impulses inside a firing neuron, which characterizes new magnetic materials and probes exotic quantum physical phenomena.

The new approach is described today in the journal Physical Review Letters in a paper by doctoral student Yi-Xiang Liu, former doctoral student Ashok Ajoy, and professor of nuclear science and technology Paola Cappellaro. [1

9659005] The technology is based on a platform that has already been developed to distinguish magnetic fields with high precision, with small defects in diamonds called nitrogen-free (NV) centers. These defects consist of two adjacent sites in the diamond ordered grid of carbon atoms lacking carbon atoms; one of them is replaced by a nitrogen atom, and the other is left empty. This leaves missing bonds in the structure, with electrons that are extremely sensitive to small variations in their environment, whether they are electric, magnetic or light based. Previous uses of individual NV centers for detecting magnetic fields have been extremely accurate but only capable of measuring these variations along a single dimension, aligned with the sensor's axis. However, for some applications, such as mapping the relationships between neurons by accurately measuring the direction of each firing pulse, it would be useful to measure the lateral portion of the magnetic field as well. Essentially, the novel method solves that problem by using a secondary oscillator provided by the nuclear atom core spin. The side component of the field to be measured attenuates the orientation of the secondary oscillator. By tapping it slightly off the axis, the side component produces a kind of cradle that appears as a periodic fluctuation of the field aligned with the sensor, which twists the perpendicular component of a wave pattern superimposed on the primary, static magnetic field measurement. This can then be mathematically converted back to determine the size of the side member.

The method gives so much precision in the second dimension as in the first dimension, Liu explains, while still using a single sensor, retaining its nanoscale spatial resolution. To read the results, the researchers use an optical confocal microscope that utilizes a particular feature of NV centers: when exposed to green light, they emit a red glow or fluorescence, the intensity of which depends on their exact spin state. These NV centers can act as qubits, the quantum compensation equivalent of the bits used in ordinary data processing.

"We can tell the spin state of the fluorescence," explains Liu. "If it's dark," produces less fluorescence ", it's a" one "state, and if it's bright, it's a" zero "state, she says." If the fluorescence is a number in between, the spin state is somewhere. between "zero" and "one." "

The needle with a single magnetic compass tells the direction of a magnetic field, but not its strength. Some existing magnetic field measuring units can do the opposite, measuring the field strength exactly along one direction, but They tell nothing about the overall orientation of the field. The real information is what the new detector system can provide.

In this new type of "compass", Liu says "we can say where it points to the brightness of fluorescence" and the variations in brightness. The primary field is indicated by the overall, stable brightness level, while the wave introduced by striking the magnetic field outside the axis appears as a common, wave-like variation of brightness which can then be measured.

An interesting application for this technique would be to put diamond NV centers in contact with a neuron, Liu says. When the cell burns its action potential to trigger another cell, the system should be able to detect not only the intensity of its signal but also its direction, which helps to map the connections and see which cells trigger which others. Similarly, when testing new magnetic materials that may be suitable for data storage or other applications, the new system should allow for a detailed measurement of the magnet and the orientation of magnetic fields in the material.

Unlike some other systems that require extremely low temperatures to work, this new magnetic sensor system can work well at normal room temperature, says Liu, which makes it possible to test biological samples without damaging them.

The technology of this new method is already available. "You can do it now, but you must first take the time to calibrate the system," Liu says. [1965] Currently, the system only provides a measurement of the total perpendicular portion of the magnetic field, not the exact orientation. "Now we just extract the total transverse component, we can't specify the direction," says Liu. But adding the third dimensional component can be done by inserting an added static magnetic field as the reference point. "As long as we can calibrate this reference field," she says, it would be possible to get the full three-dimensional information about the field orientation and "there are many ways to do it."

Amit Finkler, a senior chemical physics researcher at the Weizmann Institute of Israel, who was not involved in this work, says "This is high-quality research. They have a cross-magnetic field sensitivity similar to the DC field sensitivity , which is impressive and encouraging for practical applications. "

Finkler adds," As the authors humbly write in the manuscript, this is really the first step toward vector nanoscale magnetometry. such as molecules or condensed matter systems. "But he says:" It is like a potential user / implementer of this technology, I am very impressed and further encouraged to adopt and apply this scheme in my experimental settings. "

Explore further:
At the same time, new tools feel magnetic fields in different directions

More information:
Yi-Xiang Liu et al., Nanoscale Vector dc Magnetometry via Ancilla-Assisted Frequency Up Conversion, Physical Review Letters (2019). DOI: 10.1103 / PhysRevLett.122.100501, dx.doi.org/10.1103/PhysRevLett.122.100501

Journal reference:
Physical review letters

Provided by:
Massachusetts Institute of Technology

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