Quantum sensors, which detect the smallest differences in magnetic or electric fields, have made possible precise measurements in materials science and fundamental physics. But these sensors were only able to detect a few specific frequencies of these fields, which limited their usefulness. Now, researchers at MIT have developed a method that allows these sensors to detect any random frequency, without losing their ability to measure nanoscale features.
The new method, which the team has already submitted for patent protection, is described in the journal X . physical examinationIn an article by graduate student Guoqing Wang, professor of nuclear science, engineering and physics Paula Capellaro, and four others at MIT and Lincoln Laboratory.
Quantum sensors can take many forms; They are basically systems in which some particles in equilibrium are so sensitive that they are affected even by minute changes in the fields to which they are exposed. These can take the form of neutral atoms, trapped ions, and solid-state spins, and research using such sensors has grown rapidly. For example, physicists use it to study exotic states of matter, including so-called time crystals and topological phases, while other researchers use it to characterize practical devices such as experimental quantum memory or computing devices. But many other interesting phenomena cover a much wider range of frequencies than current quantum sensors can detect.
The new system the team developed, which they call a quantum mixer, injects a second frequency into the detector using a beam of microwaves. This converts the frequency of the field under study to a different frequency – the difference between the original frequency and the frequency of the added signal – which is tuned to the specific frequency to which the detector is most sensitive. This simple operation allows the detector to position itself at any desired frequency, without losing the spatial resolution of the sensor’s nanoscale.
In their experiments, the team used a specific device based on a set of nitrogen vacancy centers in diamond, a widely used quantum detection system, and successfully demonstrated the detection of a 150MHz signal, using a frequency qubit detector. 2.2 GHz – detection that would be impossible without a quantum multiplexer. They then performed detailed analyzes of the process by deriving a theoretical framework, based on Flockett’s theory, and testing the numerical predictions of this theory in a series of experiments.
Although their tests used this specific system, says Wang, “the same principle can also be applied to any type of quantum sensor or device.” The system will be self-contained, in which the detector and the second frequency source are combined into one device.
Wang says that this system could be used, for example, to describe the performance of a microwave antenna in detail. Can distinguish the field distribution [generated by the antenna] With nanoscale accuracy, so it’s very promising in that direction.”
There are other ways to change the frequency sensitivity of some quantum sensors, but they require the use of large devices and strong magnetic fields that blur fine details and make it impossible to achieve the very high accuracy offered by the new system. In such systems today, Wang says, “you have to use a strong magnetic field to tune the sensor, but that magnetic field can break the properties of quantum matter, which can affect the phenomena you want to measure.”
The system may open up new applications in biomedical fields, according to Capellaro, because it can give access to a range of frequencies of electrical or magnetic activity at the level of a single cell. It says it would be very difficult to obtain any useful accuracy from these signals using current quantum detection systems. It may be possible to use this system to detect the output signals of a single neuron in response to certain stimuli, for example, which usually include a lot of noise, making these signals difficult to isolate.
The system can also be used to describe in detail the behavior of exotic materials such as 2D materials that have been extensively studied for their electromagnetic, optical and physical properties.
In the work in progress, the team is exploring the possibility of finding ways to extend the system to be able to examine a range of frequencies simultaneously, rather than single-frequency targeting of the existing system. They will also continue to determine the capabilities of the system using more powerful quantum sensors at Lincoln Laboratory, where some members of the research team are.
The team included Yi Xiang Liu of the Massachusetts Institute of Technology, Jennifer Schloss, Scott Alcid and Daniel Bray of Lincoln Laboratory. The work was supported by the Defense Advanced Research Projects Agency (DARPA) and Q-Diamond.
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