Experts from the University of Bonn explained the principle of the new experiment using a simple example. Suppose you
A little trick helps him in this:while the waiter speeds up his steps, he tilts the tray slightly so that the champagne does not pour out of the glasses. Halfway to the table, he tilts it in the opposite direction and slows down. Only when it comes to a complete stop does it hold it upright again.
Atoms are somewhat like champagne.They can be described as waves of matter that do not behave like a billiard ball, but like a liquid. So anyone who wants to move atoms from one place to another as quickly as possible has to be as skillful as a waiter on New Year's Eve. “And even then there is a speed limit,” explains Dr. Andrea Alberti, who led the study at the Institute of Applied Physics at the University of Bonn.
In their study, scientists experimentallyfound out exactly where this limit is. They used a cesium atom as a champagne substitute and two laser beams perfectly superimposed but directed against each other. This superposition, which physicists call interference, creates a standing wave of light: similar to a sequence of «mountains» and «valleys», which initially do not move. “We loaded an atom into one of these valleys, and then set a standing wave in motion - this shifted the position of the valley itself,” explains Alberti. “Our goal was to deliver the atom to the right place in the shortest possible time, without splashing it out of the «valley».”
That there is a limitation in the microcosmspeed, was theoretically demonstrated by two Soviet physicists, Leonid Mandelstam and Igor Tamm, more than 60 years ago. They showed that the maximum speed of a quantum process depends on the energy uncertainty. Essentially, it depends on how “free” the controlled particle is in relation to its possible energy states: the more energy freedom it has, the faster it is. In the case of atom transfer, for example, the deeper the “valley” in which a cesium atom is trapped, the greater the spread of energies of quantum states in the valley and, ultimately, the faster it can be transferred. Something similar can be seen in the example of a waiter: if he fills glasses only halfway, he is less likely to spill champagne when he speeds up and slows down. However, the energy freedom of a particle cannot be increased arbitrarily. “We cannot make our «valley» infinitely deep - that would take too much energy,” emphasizes Alberti.
The speed limit of Mandelstam and Tamm -fundamental limitation. However, this can be achieved only under certain circumstances, namely, in systems with only two quantum states. “In our case, for example, this happens when the origin and destination are very close to each other,” explains the woman physicist. "Then the material waves of the atom in both places overlap, and the atom can be delivered directly to its destination in one go, that is, without any intermediate stops."
However, the situation changes when the distanceincreases to several tens of values of the wavelength of matter, as in the Bonn experiment. Direct teleportation is impossible at these distances. Instead, the particle must go through several intermediate states in order to reach its final destination: the two-level system becomes multi-level. The study shows that a lower speed limit applies to such processes than the two Soviet physicists predicted. The point is that it is determined not only by the uncertainty of energy, but also by the number of intermediate states. Thus, the new work improves the theoretical understanding of complex quantum processes and their limitations.
The conclusions of physicists are important not least forquantum computing. The computations that are possible with quantum computers are mainly based on the manipulation of multilevel systems. However, quantum states are very fragile. They last only a short period of time - the time of coherence. The new study reveals the maximum number of operations scientists can perform during the alignment time. This allows it to be used optimally.
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