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

Scientists from the University of Cambridge, Harvard and WITH, have shown that quantum particles can carry an unlimited amount of information about the things they interact with. The results are listed in the magazine *Natural communications*, could enable much more accurate measurements and power new technologies, such as high – precision microscopes and quantum computers.

Metrology is the science of estimates and measurements. If you weighed yourself this morning, you did metrology. In the same way as quantum calculations It is expected to cause a revolution in the way complex calculations are made, quantum metrology, using the strange behavior of subatomic particles, can cause a revolution in the way we measure things.

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, it is necessary to extend the concept of probability to include the so-called A quasi probability that can be negative. This quasi-probability makes it possible to explain quantum concepts, such as Einstein’s “haunting action at a distance” and the duality of wave particles, in intuitive mathematical language. For example, probability atom be in a certain position and travel at a specific speed can be a negative number, for example -5%.

An experiment whose explanation requires negative probabilities is said to have “quantum negativity.” Scientists have now shown that this quantum negativity can help with more accurate measurements.

The whole metrology needs probes, which can be simple scales or thermometers. In state-of-the-art metrology, however, probes are quantum particles that can be regulated at the level below the atom. These quantum particles are made to interact with the measured object. The particles are then analyzed by a detection device.

Theoretically, the larger the number of probe particles, the more information will be available to the detection device. In practice, however, there is a limit to the speed at which detection devices can analyze particles. The same is true in everyday life: wearing sunglasses can filter out excess light and improve vision. However, there is a limit to the extent to which filtering can improve our vision – having sunglasses that are too dark is harmful.

“We’ve adapted tools from standard information theory to near-probabilities, and we’ve shown that quantum particle filtering can condense information from a million particles to one,” said lead author Dr. David Arvidsson-Shukur of Camendish Cavendish Laboratory and Sarah Woodhead Fellow at Girton College. “This means that detection devices can operate at their ideal flow rate while receiving information corresponding to much higher speeds. According to normal probability theory, this is forbidden, but quantum negativity allows it. “

An experimental group at the University of Toronto has already begun building technology to take advantage of 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 modern new technologies, such as photonic quantum computers.

“Our discovery opens up exciting new ways to use fundamental quantum phenomena in real-world 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 technologies, but also to better resources for testing basic physics and improving our understanding of the universe. For example, many technologies rely on the precise alignment of components or the ability to detect small changes in electric or magnetic fields. Higher accuracy in aligning mirrors is made possible by more accurate microscopes or binoculars, and better ways of measuring the Earth’s magnetic field can lead to better navigation tools.

Quantum metrology is currently used to increase the accuracy of gravitational wave detection when winning the Nobel Prize LIGO Hanford Observatory. But for most applications, quantum metrology with current technology has been too expensive and unattainable. Newly published results offer a cheaper way of quantum metrology.

“Researchers 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 calculation price,” said co-author Aleksander Lasek, PhD candidate at Cavendish Lab. “In quantum metrology, however, this price can fall arbitrarily. This is highly counterintuitive and truly amazing! “

Nicole Yunger Halpern, co-author and postgraduate member of ITAMP at Harvard University, said: “Daily multiplication: Six times seven is equal to seven times six. Quantum theory involves propagation that is not occurring. The lack of commutation allows us to improve metrology through quantum physics.

“Quantum physics improves metrology, computation, cryptography and more; but to prove consistently that it is difficult. We have shown that quantum physics allows us to extract more information from experiments than we would only be able to do with classical physics. The key to the proof is the quantum version of probabilities – mathematical objects that are similar to probabilities, but can assume negative and unrealistic values. “

Reference: 28 July 2020, *Natural communications*.

DOI: 10,1038 / s41467-020-17559-w