Hi all,(adsbygoogle = window.adsbygoogle || []).push({});

I've been reading the seminal Zurek papers on decoherence but there is one (crucial) point on which I am confused. I understand the mathematical demonstrations that over very short timescales the superpositions of states represented as off-diagonal terms in the density matrix can be shown to go to zero over very short timescales due to interaction of the apparatus/system with the environment, leaving a diagonal density matrix. However, why exactly does a diagonal density matrix mean that we can never measure a superposition of states?

Thanks for any insight!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Decoherence and the Density Matrix

**Physics Forums | Science Articles, Homework Help, Discussion**