A group of Chinese physicists, led by Pan Jianwei, conducted an experiment that realized Albert Einstein’s classic thought experiment involving two slits and a movable detector. The work’s findings were published in the journal Physical Review Letters and, according to specialists, yield an unambiguous confirmation favoring the complementarity principle formulated by Niels Bohr.
The experiment was based on Einstein’s notion about the feasibility of simultaneously determining which slit a photon passed through while preserving the interference pattern. To test this assumption, the researchers constructed an interferometer where a solitary rubidium atom performed the role of the sensitive, moving element. It was held in a trap by laser radiation and chilled to extremely low temperatures, enabling the control of minute deviations.
In the weak external field regime, the atom could slightly shift due to the impulse of the passing photon. By analyzing the nature of this displacement, it was possible to reconstruct information about which slit the particle traversed. However, under this mode, the interference pattern on the screen vanished, signaling the destruction of coherence. Upon transitioning to a stronger field, the atom’s shift became virtually indistinguishable, the photon’s path could not be discerned, yet interference reappeared.
The acquired outcomes clearly substantiated Bohr’s complementarity principle: the attempt to precisely measure the path of a quantum particle inevitably erases information regarding its wave properties. In the opinion of the Physical Review Letters reviewers, the conducted study became one of the clearest and most technically elegant demonstrations of this fundamental tenet of quantum theory. The authors note that the refined techniques for controlling an individual atom could be utilized for further probing the loss of coherence and the mechanisms of quantum entanglement.
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