General, Research, Technology

Speed ​​limits discovered in the quantum world

If the quantum theory is correct, then from suchquantum particles like atoms, you can expect very strange behavior. But despite the chaos that quantum physics may seem like, this amazing world of tiny particles has its own laws. Recently, a team of scientists from the University of Bonn was able to prove that in the quantum world - at the level of complex quantum operations - there is a speed limit. Atoms, being small indivisible particles, in a way resemble the bubbles of champagne in a glass. They can be described as waves of matter, but their behavior is more like a billiard ball rather than a liquid. Anyone who comes up with the idea to very quickly move an atom from one place to another should act with knowledge and dexterity like an experienced waiter at a banquet - without spilling a drop of champagne from a dozen glasses on a tray, maneuvering between tables. Even so, the experimenter will be faced with a certain speed limit - a limit that cannot be exceeded. The results obtained in the course of the study are important for the operation of quantum computers, and this area, as the dear reader probably knows, has been actively developing in recent years.

Quantum physics is intriguing as it contains some mystery at its core.

Speed ​​limiting by the example of a cesium atom

In a study published in the journal PhysicalReview X, physicists were able to experimentally prove the existence of a speed limit during complex quantum operations. In the course of the work, scientists from the University of Bonn, as well as physicists from the Massachusetts Institute of Technology (MIT), the Julich Research Center, the universities of Hamburg, Cologne and Padua experimentally found out where the limitation is.

For this, the authors of the scientific work took a cesium atomand directed two perfectly superimposed laser beams against each other. The aim of the study was to deliver the cesium atom as quickly as possible to the right place so that the atom would not “fall out” from the designated “valley” like a drop of champagne from a glass. This superposition of physics is called inference, it creates a standing wave of light, which resembles an initially immovable sequence of "mountains" and "valleys". During the experiment, physicists loaded a cesium atom into one of these "valleys", and then set in motion a standing wave of light, which displaced the position of the "valley".

Standing electromagnetic wave - periodic change in the amplitude of the strength of the electric and magnetic fields along the direction of propagation, caused by the interference of the incident and reflected waves.

Study author Manolo Rivera Lam (left) and lead author Dr. Andrea Alberti (right) from the Institute of Applied Physics, University of Bonn. university.

The very fact that in the microcosm existsthe speed limit was theoretically demonstrated over 60 years ago by two Soviet physicists Leonid Mandelstam and Igor Tamm. They showed that the maximum speed in quantum operations depends on energy uncertainty, that is, on how "free" the manipulated particle is in relation to its possible energy states: the more energy freedom it has, the faster it is. For example, in the case of transporting a cesium atom, the deeper the “valley” into which the atom falls, the more distributed the energies of quantum states in the “valley”, and ultimately the faster the atom can be moved.

Something similar can be seen by carefully observingfor a waiter in a restaurant: if he fills the glasses halfway (at the request of the guest), then the chances of spilling champagne are reduced, despite the speed with which the waiter pours the drink. Nevertheless, the energy freedom of a single particle cannot be simply taken and increased. “We cannot make our 'valley' infinitely deep because it takes too much energy,” the study authors write.

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New results for science

The speed limit proposed by Mandelstamand by Tamm the fundamental. However, it can be achieved under certain circumstances, namely, in systems with only two possible quantum states. In the case of this study, for example, this happened when the point of departure and the point of destination were extremely close to each other. “Then the waves of matter of the atom in both places are superimposed on each other, and the atom can be delivered directly to its destination in one go, that is, without any intermediate stops. This is similar to the teleportation in Star Trek, the study authors told

And yet, the situation changes when the distancebetween the point of departure and destination, it increases to several tens of values ​​of the wave of matter, as in an experiment by researchers from the University of Bonn. Direct teleportation is impossible at such distances. Instead of teleportation, in order to reach its destination, the particle must travel a number of intermediate distances: and it is here that the situation changes from two-level to multi-level.

See also: Can quantum mechanics explain the existence of spacetime?

The world of atoms has its own laws, often incomprehensible and invisible to an outside observer.

The research results showed that suchprocesses apply a lower speed limit than the Soviet scientists designated: it is determined not only by the uncertainty of energy, but also by the number of intermediate states. All of the above means that new research improves theoretical understanding of complex quantum processes and constraints.

Atoms and quantum computers

As physicists note, the results obtainedapplicable in the field of quantum computers. This is because the experiment carried out is devoted to the transfer of an atom, and similar processes occur in a quantum computer. When quantum bits are implemented by atoms, they must be transferred from one area of ​​the processor to another. This is exactly the process that needs to be done very quickly, otherwise all its coherence will disappear. Thanks to the quantum speed limit, you can now accurately predict what speed is theoretically possible.

This is what an IBM 50-qubit quantum computer looks like.

For quantum computers, however, thethe results do not mean a limit on computational speed. The fact that a quantum computer can compute so quickly is not primarily related to the duration as such, but rather to the number of operations. A quantum computer needs far fewer operations to complete a given task than a conventional computer. Computing with a quantum computer is like finding a way out of a maze without having to consistently check all possible paths. This is exactly what acceleration lies in: you only need to send a quantum computer through the maze once, while with a classical computer you need to try out a very large number of options one after another.

You will be interested: A quantum computer was created in China that solved the most difficult problem in 200 seconds

According to study lead author AndreaAlberti, in this sense, there are no implications for the computing power of a quantum computer. But the quantum speed limit is interesting for another reason - the discovered limit shows that it is possible to perform a much larger number of operations than previously thought.