PerspectivePhysics

Electronically erased

Science  20 Jun 2014:
Vol. 344, Issue 6190, pp. 1344-1345
DOI: 10.1126/science.1255501

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Summary

The fate of Schrödinger's cat depends on the particular path of a single electron. If the electron hits the trigger, which opens a bottle of poisonous gas, then the cat dies. If the path misses the trigger, the cat lives. According to quantum mechanics, electrons do not normally follow a definite trajectory. Instead, an electron can trace both paths at the same time. As a result, Schrödinger's cat is both dead and alive. Quantum mechanics also teaches us that a “which-path” detector—that is, any measurement device that can show where the electron travels—forces the electron to choose just one path, thus sealing the cat's destiny. But what will happen after the information collected by the detector has been erased? The results of a semiconductor version of such an experiment, reported by Weisz et al. on page 1363 of this issue (1), suggest that the cat will come back to the middle ground between life and death.