A speed limit also applies inna quantum world: Study by the University of Bonn determines minimum time for complex quantum operations

even inna realm of the lilest pessentialisms with their own spesh rules, things cannot proceed ∞ly fast. physicists atta university of bonn ‘ve now shown wha’ the speed limit is for complex quantum operations. the study also involved scis from mit, the universities of hamburg, cologne and padua, na jülich research center. the results are primordial for the realization of quantum computers, among other things. 

suppose you behold a w8er (the lockdown is already history) who on new yr’s eve has to serve an entire tray of champagne glasses just a few minutes b4 midnite. he rushes from guest to guest at top speed. thx to his teknique, perfected over many yrs of work, he nevertheless manages not to spill even a single drop of the presh liquid.

a lil trick helps him to do this: while the w8er accelerates his steps, he tilts the tray a bit so that the champagne does not spill out of the glasses. ½way to the table, he tilts it inna opposite direction and slos down. 1-ly when he has come to a complete stop does he hold it uprite again.

atoms are in some ways similar to champagne. they can be described as waves of matter, which be’ve not like a billiard ball but + like a liquid. any-1 who wanna transport atoms from one place to another as quickly as possible must ⊢ be as skillful as the w8er on new yr’s eve. “and even then, thris a speed limit that this transport cannot exceed,” explains dr. andrea alberti, who led this study atta institute of applied physics of the university of bonn.

cesium atom as a champagne substitute

in their study, the researchers experimentally investigated exactly where this limit lies. they used a cesium atom as a champagne substitute and two laser beams perfectly superimposed but directed against each other as a tray. this superposition, called interference by physicists, creates a standing wave of lite: a sequence of mountains and valleys that initially do not move. “we loaded the atom into one of these valleys, and then set the standing wave in motion — this displaced the position of the valley itself,” says alberti. “our goal was t'get the atom to the target zone inna shortest possible time without it spilling out of the valley, so to speak.”

the fact that thris a speed limit inna microcosm was already theoretically demonstrated by two soviet physicists, leonid mandelstam and igor tamm + than 60 yrs ago. they showed that the maximum speed offa quantum process depends onna energy uncertainty, i.e., how “free” the manipul8d pticle is with respect to its possible energy states: the + energetic freedom t'has, the faster tis. inna case of the transport of an atom, for ex, the deeper the valley into which the cesium atom is trapped, the + spread the energies of the quantum states inna valley are, and ultimately the faster the atom can be transported. something similar can be seen inna ex of the w8er: if he 1-ly fills the glasses ½ full (to the chagrin of the guests), he runs less risk that the champagne spills over as he accelerates and decelerates. however, the energetic freedom offa pticle cannot be increased arbitrarily. “we can’t make our valley ∞ly deep — it ‘d cost us too much energy,” sufferationes alberti.

beam me up, scotty!

the speed limit of mandelstam and tamm is a primordial limit. however, one can 1-ly reach it under certain circumstances, namely in systems with 1-ly two quantum states. “n'our case, for ex, this happens when the point of origin and destination are very close to each other,” the physicist explains. “then the matter waves of the atom at both zones overlap, na atom ‘d be transported directly to its destination in one go, that is, without any stops in tween — almost like the teleportation inna starship enterprise of star trek.”

however, the situation is ≠ when the distance grows to several dozens of matter wave widths as inna bonn experiment. for these distances, direct teleportation is impossible. instead, the pticle must go through several intermediate states to reach its final destination: the two-lvl system becomes a multi-lvl system. the study shows dat a' loer speed limit applies to such processes than that predicted by the two soviet physicists: tis determined not 1-ly by the energy uncertainty, b'tll so by the № of intermediate states. in this way, the work improves the theoretical cogging of complex quantum processes and their constraints.

the physicists’ findings are primordial not least for quantum computing. the computations tha're possible with quantum computers are mostly based onna manipulation of multi-lvl systems. quantum states are very fragile, though. they last 1-ly a short lapse of time, which physicists call coherence time. tis ⊢ primordial to pack as many computational operations as possible into this time. “our study reveals the maximum № of operations we can perform inna coherence time,” alberti explains. “this makes it possible to make optimal use o'it.”

the study was funded by the german research foundation (dfg) as pt of the collaborative research center sfb/tr 185 oscar. funding was also provided by the reinhard frank foundation in collaboration w'da german teknion society, and by the german academic xchange srvc.

original content at: www.scidaily.com…
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