“Quantum Negativity” will help develop ultra-precise measuring instruments

Scientists at Harvard and Cambridge Universities, along with colleagues at MIT and the University of Toronto, have found that a physical property called “quantum negativity” can be used to make more accurate measurements. “Measurements of what?” – readers will ask. Scientists say literally everything: from molecular distances to gravitational waves.

The scientists published an article on the results of their research in the journal Nature Communications. The use of a new phenomenon could revolutionize quantum metrology – a science that deals with the problems of measuring various quantities based on quantum effects.

Most people familiar with the concept of probability are used to the fact that this value varies from 0 to 100% – or from 0 to 1. However, to explain the results from the quantum world, the concept of probability has to be expanded to include the so-called quasi-probability, which can be negative.

For example, the probability that an atom is in a certain position and moving at a certain speed can be -5%. And an experiment, the explanation of which requires the introduction of negative probabilities, has “quantum negativity”.

In turn, the main instrument of metrology is sensors. Most often these are ordinary household appliances, such as scales and thermometers. But in quantum metrology, everything is different: here the role of sensors is played by quantum particles, which can be controlled at the subatomic level and which can be detected using special detectors.

In theory, the more probing quantum particles are available for measurements, the more information the detector can eventually receive. But in practice, there is a limit to the speed at which the detectors are able to analyze particles. This can be illustrated by an example from everyday life: wearing sunglasses, we filter out excess light and see better, but too dark glasses harm our eyes and do not allow us to see the surrounding space normally.

“We adapted tools from standard information theory to quasiprobabilities and showed that filtering quantum particles can help collect information from a million particles into one”, says lead author Dr. David Arvidsson-Shukur. “This means that detectors can operate at the ideal particle flow rate, receiving information corresponding to higher processing rates. Quantum negativity makes this possible”.

An experimental group at the University of Toronto has already begun to create technologies for the practical use of new theoretical results. The goal of the scientists will be to create a quantum device that uses single-photon laser light to provide incredibly accurate measurements of optical components. These measurements are critical to the creation of advanced devices such as photonic quantum computers.

In fact, this quantum approach allows one to extract more information from experiments than the methods and principles of classical physics. “Scientists often say that there is no free lunch. This means that you can’t get anything if you don’t want to pay the computational price, ”says study co-author Alexander Lazek. “However, in quantum metrology, this price can be made arbitrarily low. This is very illogical and really amazing”!

More accurate measurements in quantum metrology can not only lead to the creation of new advanced technologies but also give impetus to research in the field of fundamental physics and the Universe. Better alignment of mirrors and lenses will lead to more accurate microscopes or telescopes, and better ways to measure the earth’s magnetic field will lead to better navigation instruments.