It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
If macrorealism were true, repeated measurements, at different times, of a single macroscopic system would only be statistically correlated up to a certain degree, giving what they called the Leggett–Garg (LG) inequality.
"According to [macrorealism], the [object] always moves on a specific trajectory, independent of our observation," says Andrea Alberti at the University of Bonn, Germany.
By carrying out this "null result" measurement technique in the middle step, the researchers could determine the atom's location without directly interacting with it. By repeating this experiment many times, and seeing when the fluorescence is detected, the researchers can tell which wave the atom was in (and therefore its position) and also that the atom was not disturbed in any way. If macrorealism was true, the null measurement would not affect the outcome of the final fluorescence measurement, and the total amount of correlation of the atom's position in time could be explained classically – but this is not the case. Indeed, the blurring that happens in the quantum walk leads to a stronger total correlation than is possible under macrorealism. This is mathematically demonstrated via the LG inequality violation, clearly showing that macrorealism cannot apply to the caesium atom.
The results of Alberti's experiment seem to nail down for sure that a caesium atom obeys the laws of quantum mechanics, and that macrorealism does not apply. In the future, similar experiments with even larger masses and with longer superposition times will help to either narrow down the inherent boundary that lies between the quantum and classical world, or banish it once and for all and lay the foundations for a more advanced quantum theory.
If, instead, it is in spin-down state, it is transported far off so that its further evolution until the final position measurement is made cannot possibly influence the evolution of a particle that was left undisturbed. If the atom then fails to light up when the final fluorescence measurement is made, we know that the atom was in the spin-down state and was therefore discarded.