'This physical property can be used to make more precise measurements, which in turn can lead to advance technology like quantum computers. Quantum laser light shines on to a chemical molecule that needs to be measured. The light then passes through the quantum filter, which discards a lot of the light and condenses the useful information in a light that reached the camera. (Image credit: Hugo Lepage)


Scientists recently discovered a physical property, coined "quantum negativity," that can be used for more precise measurements and may even power new technologies. Researchers from Harvard, Massachusetts Institute of Technology (MIT), and the University of Cambridge found that quantum particles are able to carry an unlimited amount of information about the materials they interact with. This information can then be used for precise measurements of everything from gravitational waves to magnetic fields.


The study, published in the journal Nature Communications, proposed a way to improve the rate of Fisher information – the average information that an unknown parameter carried by a variable from a trial to cost through post-selection. This improvement is the result of "the negativity of a particular quasi-probability distribution," which is a quantum extension of the conventional probability distribution.


Researchers differentiated classical probabilities, which have real and non-negative values, and quantum probabilities, whose values can have negative and non-real positions. It's this quasi-probability that allows negative probabilities, which are used to explain concepts like quantum entanglement. Experiments that are explained through the use of negative quasi-probabilities create the "quantum negativity."


Currently, an experimental group from the University of Toronto in Canada is testing the theoretical results by creating a quantum device that uses a single-photon laser that provides precise measurements of optical components. If it works, it will allow the creation of advanced technologies, such as quantum computers.


This recent discovery greatly benefits metrology, the science of measurements and estimations. These precise measurements can improve measurements of things like distances, angles, and temperatures. These ultra-precise measurements are important in advancing physics experiments, like measuring electric and magnetic field fluctuations. The use of quantum negativity also offers a cheaper way of doing quantum metrology, which is expensive and difficult to do with current technology.


"Quantum physics enhances metrology, computation, cryptography, and more; but proving rigorously that it does is difficult," said Dr. Nicole Yunger Halpern, co-author and ITAMP Postdoctoral Fellow at Harvard University. "We showed that quantum physics enables us to extract more information from experiments than we could with only classical physics. The key to the proof is a quantum version of probabilities—mathematical objects that resemble probabilities but can assume negative and non-real values."


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