Protective measurements: probing single quantum systems

摘要

Making measurements on single quantum systems is considered difficult, almost impossible if the state is a priori unknown. Protective measurements suggest a possiblity to measure single quantum systems and gain some new information in the process. Protective measurement is described here, both in the original and generalized form. The degree to which the system and the apparatus remain entangled in a protective measurement, is assessed. Possible exterimental tests of protective measurements are also discussed.