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Spontaneous emission entropy

  1. Mar 18, 2015 #1


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    Does entropy increase during spontaneous emission?

    If not, how is the information about the emitted photon mode encoded into the initial state of the atom (and/or environment)? If so, where does the extra information come from?
  2. jcsd
  3. Mar 18, 2015 #2


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    Staff: Mentor

    Yes. And the corollary is that you cannot achieve laser cooling of atoms with stimulated emission alone, you need spontaneous emission.
  4. Mar 19, 2015 #3


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    The answer depends on what kind of entropy do you have in mind. Do you mean entropy of the total closed system, or entropy of the subsystem (e.g. atom and photon, but without environment)? If you mean the former, then von Neumann entropy does not change, and information is encoded in the entanglement with environment. If you mean the latter, then von Neumann entropy increases, provided that you describe the system with the mixed state without a projection to the measured state.
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