This is the third part of the "Nifty Papers" series. Link to Part 1. Link to Part 2.

In 1999, I was in the middle of writing about quantum information theory with my colleague Nicolas Cerf. We had discovered that quantum conditional entropy can be negative, discussed this finding with respect to the problem of quantum measurement,separability, Bell inequalities, as well as the capacity of quantum channels. Heady stuff, you might think. But we were still haunted by Hans Bethe's statement to us that the discovery of negative conditional entropies would change the way we perceive quantum statistical physics. We had an opportunity to write an invited article for a special issue on Quantum Computation in the journal "Chaos, Solitons, and Fractals", and so we decided to take a shot at the "Quantum Statistical Mechanics" angle.