Quantum Mechanics: Foundations

When one thinks about fundamental tests of the principles of quantum mechanics, the area of condensed matter physics is not the first that springs to mind. At least at first sight, such tests would seem to require the use of physical systems which are very well characterized, well isolated from their environments, and (for certain kinds of tests) propagate at or close to the speed of light. None of these conditions is at all well satisfied by a typical condensed matter system. Nevertheless, there are certain kinds of fundamental tests for which such systems are indispensable and others for which they permit substantial extensions of the results obtained on more ‘‘microscopic’’ systems, and this is the subject of this article. The issues of ‘‘quantum statistics’’ discussed are: one aspect of nonlocality in quantum mechanics, and the universal validity of the quantum description.