**Scientists have found that a physical property called “quantum negative” can be used to more accurately measure everything from molecular distances to gravitational waves.**

Researchers from Cambridge University, Harvard and WITH, showed that quantum particles can carry an unlimited amount of information about things with which they interacted. The results reported in the journal *The nature of communications*, can enable much more accurate measurements and powerful new technologies such as high-precision microscopes and quantum computers.

Metrology is the science of estimation and measurement. If you weighed yourself this morning, you did the metrology. Just like quantum calculations It is expected that a revolutionary way of performing complex calculations, quantum metrology, using the strange behavior of subatomic particles, can change the way things are measured.

We are used to dealing with probabilities that range from 0% (never happens) to 100% (always happens). However, to explain the results from the quantum world, the concept of probability needs to be expanded to include the so-called quasi-probability, which can be negative. This quasi-probability allows quantum to explain such concepts as “Einstein’s eerie action at a distance” and the duality of particle waves to be explained in intuitive mathematical language. For example, the probability of occurrence atom being in a certain position and traveling at a certain speed, this can be a negative number, for example, -5%.

It is said that an experiment, the explanation of which requires negative probabilities, has a “quantum negative”. Scientists have now shown that this quantum negative can help make more accurate measurements.

All metrology requires probes, which can be simple scales or thermometers. However, in modern metrology, probes are quantum particles that can be controlled at the subatomic level. These quantum particles are made to interact with the thing being measured. The particles are then analyzed by a detection device.

Theoretically, the more probing particles there are, the more information will be available to the detection device. But in practice, there is a limit to the speed at which detection devices can analyze particles. The same goes for everyday life: by wearing sunglasses, you can filter out excess light and improve vision. But there is a limit to how much filtration can improve our vision – too dark sunglasses are harmful.

“We’ve adapted tools from standard information theory to quasi-probabilities and shown that quantum particle filtering can condense the information of a million particles into one,” said lead author Dr. David Arvidsson-Shukur of Cambridge’s Cavendish Laboratory and researcher at Sarah Woodhead College. “This means that detection devices can operate at the ideal tide speed, receiving information that corresponds to a much higher speed. According to normal probability theory, this is forbidden, but quantum negativity makes it possible.

An experimental team at the University of Toronto has already begun building technology to use these new theoretical results. Their goal is to create a quantum device that uses single-photon laser light to provide incredibly accurate measurements of optical components. Such measurements are crucial for the creation of new advanced technologies, such as photon quantum computers.

“Our discovery opens up exciting new ways to use fundamental quantum phenomena in real applications,” said Arvidsson-Shukur.

Quantum metrology can improve the measurement of things, including distances, angles, temperatures, and magnetic fields. These more accurate measurements can lead to better and faster technology, as well as better resources for studying fundamental physics and improving understanding of the universe. For example, many technologies rely on the precise alignment of components or the ability to feel small changes in electric or magnetic fields. Higher alignment accuracy of mirrors can provide more accurate microscopes or telescopes, and better ways to measure the Earth’s magnetic field can lead to better navigation instruments.

Quantum metrology is currently used to increase the accuracy of gravitational wave detection in the Nobel Prize LIGO Hanford Observatory. But for most applications, quantum metrology has been overly expensive and unattainable with modern technology. The newly published results offer a cheaper way to implement quantum metrology.

“Scientists often say that ‘there is no such thing as a free lunch,’ which means you can’t get anything if you don’t want to pay the price for the calculation,” said co-author Alexander Lasek, Ph.D. at Cavendish Laboratory. “However, in quantum metrology, this price can be arbitrarily low. It’s extremely counterintuitive and truly amazing!”

Dr Nicole Junger Halpern, co-author and PhD student at ITAMP at Harvard University, said: “Daily multiplication varies: Six times seven equals seven times six. Quantum theory assumes multiplication that does not change. The lack of switching allows us to improve metrology using quantum physics.

“Quantum physics improves metrology, computing, cryptography, etc .; but it is difficult to prove rigidly that this is being done. We have shown that quantum physics allows us to obtain more information from experiments than we could with classical physics alone. The key point is the quantum version of probabilities – mathematical objects that resemble probabilities but can take negative and unrealistic values. “

Reference: July 28, 2020, *The nature of communications*.

DOI: 10.1038 / s41467-020-17559-w