The new system allows these nanoscale sensors to detect tiny fluctuations in electromagnetic fields across every frequency.
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Quantum sensors give researchers unprecedented insight into the subatomic world and have a wealth of potential applications ranging from cancer detection, the mapping of biological processes, and even geological exploration.
Perhaps the most exciting application of quantum sensors is in the search for quantum materials or exotic materials that could form the foundation of large-scale quantum computers.
There is a lingering problem with these devices that detect variations in electromagnetic fields to enable precise measurements that can be used in materials science and even in the investigation of fundamental physics. Quantum sensors have thus far been restricted to collecting measurements in limited regions of the electromagnetic spectrum, something that has limited their usefulness.
This limitation could soon be a thing of the past thanks to researchers at the Massachusetts Institute of Technology (MIT) and Lincoln Laboratory. The MIT-led team has developed a method that allows quantum sensors to be deployed to measure variations in any frequency of electromagnetic radiation without a loss of sensitivity to nanoscale-sized features.
The team’s new method is described in a paper published in the journal Physical Review X.
What is a Quantum Mixer?
Quantum sensors come in a wide range of forms, with a common theme being the nature of their systems. They are based upon a system in which some particles exist in a delicately balanced state. This means that these particles can be disturbed by the slightest variation in the fields to which they are exposed.
It is therefore quite ironic that the delicate and easily disturbed states of a quantum system that majorly disadvantage quantum computers are actually a bonus to quantum sensors.
The team devised a system that they call a quantum mixer. This introduces a second frequency in the quantum sensor using microwave beams. The result is the conversion of the studied field’s frequency to another frequency.
This resultant frequency is equal to the difference between the original studied frequency and the second newly introduced frequency. This resultant frequency is also one that the quantum sensor is primed to detect.
The deceptively simple approach means that a quantum sensor could target any frequency of electromagnetic radiation without suffering a loss of resolution.
Developing a Quantum Mixer
To test their new system, the researchers used a device that utilizes a common quantum sensing system — namely an array of nitrogen-vacancy centers in diamond.
With the aid of the quantum mixer, a qubit — the foundational unit of a quantum computer — with a frequency of 2.2 gigahertz was able to detect a signal at a frequency of 150 megahertz. This is something that would have otherwise been impossible.
Though the tests conducted by the team focused on a specific system, the researchers are confident that the same principle can be applied to any type of quantum sensor. They envision the detector and second frequency generator encompassed in the same, relatively compact device.
The beauty of the system devised by the team is that it can change the frequency of the field to be studied without the need for strong magnetic fields that can smear out fine details making obtaining high-resolution measurements impossible or influencing the quantum phenomena that are to be measured.
Because of the range of frequencies available to this new system the team says it opens up a range of new applications for quantum sensors. These could include obtaining electromagnetic readings at the level of a single cell — not possible with current technology.
One example given by the team is the detection of the response of a single neuron to some stimulus, usually not possible because of the amount of noise associated with such signals.
With regard to materials science, the system could be used to investigate the optical, electromagnetic, and physical properties of 2D materials — materials that could be of use in quantum computers.
The next step for the team will be to find a way for the system to investigate multiple frequencies simultaneously, expanding it beyond its capability to investigate one frequency at a time.
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Reference and Further Reading
Wang. G., Liu. Y-X., Schloss. J. M., et al, , “Sensing of Arbitrary-Frequency Fields Using a Quantum Mixer,” Physical Review X, [https://journals.aps.org/prx/abstract/10.1103/PhysRevX.12.021061]