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Pure/mixed state

  1. Oct 9, 2007 #1

    I read the following statement somewhere:

    "... we study the entaglement of the ground state and the mixed state at finite temperatures ..."

    Does this mean that the ground state of a system is always pure? :confused:

  2. jcsd
  3. Oct 9, 2007 #2
    Any state that can be represented by a vector in the Hilbert space (e.g., any solution of the stationary Schroedinger equation, including the ground state solution) is a pure quantum state.

  4. Oct 9, 2007 #3


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    Mixed state are important when you study statistical properties of a system. I.e. the density matrix describes the property of an ensemble (which is why the . Hence, a mixed state does not describe a "proper" state as such.
    You can also get what is sometimes known as an "improper" mixture if you study a specific subsystem of a composite system by tracing out all other degrees of freedom.
  5. Oct 9, 2007 #4


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    Double post
    Last edited: Oct 9, 2007
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