Quantum mechanics impose a limit on what we can know about subatomic particles. If physicists measure the position of a particle, they cannot measure its momentum, as the theory says. However, in the course of the new experiment, as reported by ScientificAmerican, it was possible to circumvent this rule - the so-called uncertainty principle - by learning about the position of the particle quite a bit, and thereby retaining the possibility of measuring the momentum.
The uncertainty principle formulated by Werner Heisenberg in 1927 shows true wonders of nature on a microscopic scale. Quantum mechanics has shown that particles are not just tiny balls that act like ordinary objects, which we can see and touch. Elementary particles exist in a fog of probability, instead of being in a certain place at a certain time. Their chances of being in any particular state are described by the equation of a quantum wave function. Any measurement of a particle causes the wave function to "collapse", to choose a specific value.
Not so long ago, physicists decided to see if they could overcome this limitation using a new engineering technique called compressive sensing - a technique for receiving and restoring a signal based on knowledge of its previous values, which are sparse or compressed. This tool has long been used for effective calculations in the field of digital photography, MRI scanning and other technologies. As a rule, measuring devices carry out a detailed reading, and then compress the data for ease of use. For example, cameras take large images in RAW format, and then convert them to a more compressed JPEG format. In compressed probing, however, engineers tend to compress the signal during the measurement, which allows them to take fewer measurements — as if they were making JPEG photos rather than RAW.
The same method of obtaining the minimum information necessary for measurement was proposed as a way to circumvent the uncertainty principle. To test the work of compressive sensing in the quantum world, physicist John Howell and his team at the University of Rochester measured the coordinates and momentum of a photon — particles of light. They let the laser through a box filled with a series of mirrors that could be directed both to and from the detector. These mirrors formed a filter that allowed photons to penetrate one place and remain blocked in others. If the photon was in the detector, physicists knew that it was in one of the places where mirrors opened a free path. Such a filter gave scientists the opportunity to measure the position of a particle without actually knowing about it, without allowing the wave function to collapse.
“All that we knew was whether the photon was able to follow this path or not,” says Gregory Howland, author of a work on this topic, published in the beginning of summer in the journal Physical Review Letters. “So, as a result, we still could measure the momentum of the photon.” However, in the course of such a measurement, we received some noise. But a less accurate pulse measurement is still better than none. ”
Physicists emphasize that they did not violate the laws of physics.
“We did not violate the uncertainty principle,” says Howland. “We just used it wisely.”
This technique can give a powerful impetus to the development of technologies such as quantum cryptography and quantum computers, which seek to use the quantum properties of particles as useful applications. The more information that can be obtained in the course of quantum measurements, the better such technologies will work. The Howland experiment can lead to more efficient quantum measurements than was possible before. In simple terms, physicists have found a way to get more data by taking fewer measurements.
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