Violation of a Leggett–Garg inequality withideal non-invasive measurements

摘要

The quantum superposition principle states that an entity can exist in two different statessimultaneously, counter to our ‘classical’ intuition. Is it possible to understand a given system’sbehaviour without such a concept? A test designed by Leggett and Garg can rule out thispossibility. The test, originally intended for macroscopic objects, has been implemented invarious systems. However to date no experiment has employed the ‘ideal negative result’measurements that are required for the most robust test. Here we introduce a general protocolfor these special measurements using an ancillary system, which acts as a local measuringdevice but which need not be perfectly prepared. We report an experimental realization usingspin-bearing phosphorus impurities in silicon. The results demonstrate the necessity of a nonclassical picture for this class of microscopic system. our procedure can be applied to systemsof any size, whether individually controlled or in a spatial ensemble.