Distinguishability of non-orthogonal density matrices does not imply violations of the second law
Abstract
Description
The hypothetical possibility of distinguishing preparations described by non-orthogonal density matrices does not necessarily imply a violation of the second law of thermodynamics, as was instead stated by von Neumann. On the other hand, such a possibility would surely mean that the particular density-matrix space (and related Hilbert space) adopted would not be adequate to describe the hypothetical new experimental facts. These points are shown by making clear the distinction between physical preparations and the density matrices which represent them, and then comparing a "quantum" thermodynamic analysis given by Peres with a "classical" one given by Jaynes.
LaTeX2e, RevTeX4, 10 pages, 6 figures. V2: small changes, additional references, and additional note on the issue of the "reduced dynamics" of "open quantum systems initially entangled with the environment". V3: additional changes and references. V4: amply extended introduction with discussion of "quantum" ideal gases and semi-permeable membranes
LaTeX2e, RevTeX4, 10 pages, 6 figures. V2: small changes, additional references, and additional note on the issue of the "reduced dynamics" of "open quantum systems initially entangled with the environment". V3: additional changes and references. V4: amply extended introduction with discussion of "quantum" ideal gases and semi-permeable membranes