MIT Quantum Sensor Can Detect Electromagnetic Signals of Any Frequency
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Scientists at MIT have developed a method to enable such quantum sensors to detect arbitrary frequencies, without losing their ability to measure nanometer-scale features.
The new method is described in a paper published in the journal Physical Review X by graduate student Guoqing Wang, professor of nuclear science and engineering and of physics Paola Cappellaro, and four others at MIT and Lincoln Laboratory. The team has already applied for patent protection for the new method.
Although quantum sensors can take many forms, at their essence they’re systems in which some particles are in such a delicately balanced state that they are affected by even tiny variations in the fields they are exposed to. 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 them to investigate exotic states of matter, including so-called time crystals and topological phases, while other scientists use them to characterize practical devices such as experimental quantum memory or computation devices. However, many other phenomena of interest span a much broader frequency range than today’s quantum sensors can detect.
MIT researchers have developed a method to enable quantum sensors to detect any arbitrary frequency, with no loss of their ability to measure nanometer-scale features. Quantum sensors detect the most minute variations in magnetic or electrical fields, but until now they have only been capable of detecting a few specific frequencies, limiting their usefulness. Credit: Guoqing Wang
The new system the team devised, 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 being studied into a different frequency — the difference between the original frequency and that of the added signal — which is tuned to the specific frequency that the detector is most sensitive to. This simple process enables the detector to home in on any desired frequency at all, with no loss in the nanoscale spatial resolution of the sensor.
In their experiments, the team used a specific device based on an array of nitrogen-vacancy centers in diamond, a widely used quantum sensing system, and successfully demonstrated the detection of a signal with a frequency of 150 megahertz, using a qubit detector with a frequency of 2.2 gigahertz — a detection that would be impossible without the quantum multiplexer. They then did detailed analyses of the process by deriving a theoretical framework, based on Floquet theory, and testing the numerical predictions of that theory in a series of experiments.
While their tests used this specific system, Wang says, “the same principle can be also applied to any kind of sensors or quantum devices.” The system would be self-contained, with the detector and the source of the second frequency all packaged in a single device.
Wang says that this system could be used, for example, to characterize in detail the performance of a microwave antenna. “It can characterize the distribution of the field [generated by the antenna] with nano resolution, so it’s very promising in that direction,” he said.
There are other ways to change the frequency sensitivity of some quantum sensors, but these require the use of bulky devices and strong magnetic fields that obscure fine details and make it impossible to achieve the ultra-high resolution that the new system offers. In such a system today, Wang said, “You need to use a strong magnetic field to tune the sensor, but that magnetic field has the potential to damage the quantum material properties, which can affect the phenomena you want to measure.”
The system could open up new applications in the biomedical field, according to Cappellaro, because it can make the frequency range of electrical or magnetic activity accessible at the single-cell level. It would be very difficult to get a useful resolution of the signal using current quantum sensing systems, he said. It is possible to use this system to detect the output signal of a single neuron in response to several stimuli, for example, which usually includes a lot of noise, making the signal difficult to isolate.
The system can also be used to characterize in detail the behavior of exotic materials such as 2D materials which are being intensively studied for their electromagnetic, optical and physical properties.
In ongoing work, the team is exploring the possibility of finding ways to extend the system to be able to probe multiple frequencies at once, rather than targeting the current system’s single frequency. They will also continue to determine the system’s capabilities using more powerful quantum sensing devices at the Lincoln Laboratory, where several members of the research team are located.
Reference: “Sensing Arbitrary Frequency Fields Using a Quantum Mixer” by Guoqing Wang, Yi-Xiang Liu, Jennifer M. Schloss, Scott T. Alsid, Danielle A. Braje and Paola Cappellaro, June 17, 2022, X Physical Overview.
DOI: 10.103/PhysRevX.12.021061
The team includes Yi-Xiang Liu at MIT and Jennifer Schloss, Scott Alsid and Danielle Braje at Lincoln Laboratory. This work was supported by the Defense Advanced Research Projects Agency (
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