Abstract
The state of an isolated quantum system has hitherto been represented by a vector in the state space. We shall see that it can also be represented by a Hermitian operator called the density operator. The usefulness of that operator comes from the fact that it can represent not only the state of an isolated system, but also the state of a system that genuinely interacts with the environment, or even the state of an ensemble of systems prepared in different ways. We will introduce the notion of tensor product of vector spaces, a mathematical tool well adapted to the description of a system made of two or more subsystems. The density operator finds a particularly important application in statistical physics. It will also be used to introduce the notion of history, useful for the clarification of interpretation questions.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Preview
Unable to display preview. Download preview PDF.
Author information
Authors and Affiliations
Rights and permissions
Copyright information
© 2002 Springer-Verlag Berlin Heidelberg
About this chapter
Cite this chapter
Marchildon, L. (2002). The Density Operator. In: Quantum Mechanics. Advanced Texts in Physics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-04750-7_12
Download citation
DOI: https://doi.org/10.1007/978-3-662-04750-7_12
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-642-07767-8
Online ISBN: 978-3-662-04750-7
eBook Packages: Springer Book Archive