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“Quantum negativity” can lead to very accurate measurements



Quantum laser light shines on the chemical molecule we want to measure. Then light passes through our “magic”

; quantum filter. This filter sheds a lot of light and condenses all the useful information in low light that the camera detector eventually reaches. Credit: Hugo Lepage

The researchers found that a physical property called “quantum negativity” could be used to more accurately measure everything from molecular distances to gravitational waves.

Researchers at the University of Cambridge, Harvard and MIT 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 that quantum computations are expected to revolutionize the way complex computations are made, quantum metrology, through the strange behavior of subatomic particles, can revolutionize 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, the probability that an atom will be in a certain position and travel at a specific velocity may 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 subatomic level. 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 – it is harmful to have sunglasses.

“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. This is forbidden by normal probability theory, 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 of using 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 at the Nobel Prize-winning 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 pay the calculation price,” said co-author Aleksander Lasek, Ph.D. candidate at Cavendish Laboratory. “However, in quantum metrology, this price can be arbitrarily low. That’s very counterintuitive and really amazing! “

Nicole Yunger Halpern, co-author and ITAMP postgraduate colleague at Harvard University, said: “Daily multiplication: Six times seven equals seven times six. Quantum theory involves multiplication that does not change. using quantum physics.

“Quantum physics improves metrology, computations, cryptography and more; however, we have strictly proved 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. ‘ ”


Final limit of accuracy of multimetric quantum magnetometry


More information:
Natural communications (2020). DOI: 10,1038 / s41467-020-17559-w

Provided by the University of Cambridge



Citations: “Quantum Negativity” May Lead to Very Accurate Measurements (2020, July 29) Obtained on July 29, 2020 from https://phys.org/news/2020-07-quantum-negativity-power-ultra-precise.html

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