A First Introduction to Quantum Physics pp 115-138 | Cite as

# Decoherence

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## Abstract

In this chapter, we ask what happens when a quantum system is in contact with its environment. To describe this, we need a more general concept of the quantum state, namely the density matrix. We study the density matrix, and how it describes both classical and quantum uncertainty. This also naturally leads to a description of quantum systems at a non-zero temperature. We conclude this chapter with a short discussion on how entropy arises in quantum mechanics.

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## References

- R. Landauer, Irreversibility and heat generation in the computing process. IBM J. Res. Dev.
**5**, 183 (1961)MathSciNetCrossRefGoogle Scholar - L. Szilard, Über die Entropieverminderung in einem thermodynamischen System bei Eingriffen intelligenter Wesen. Zeitschrift für Physik
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