Expected Value Partial Trance Density Matrix

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Discussion Overview

The discussion revolves around a step in the derivation of the expected value in quantum mechanics, specifically involving the trace operation on a partial density matrix. The focus is on understanding the notation and the mathematical steps involved in the calculation.

Discussion Character

  • Technical explanation

Main Points Raised

  • One participant expresses difficulty in understanding a specific step in the derivation involving the expected value and the trace operation.
  • Another participant clarifies that 'tr' refers to 'trace', suggesting a possible misunderstanding of the term.
  • A third participant agrees with the clarification about 'tr' standing for 'trace'.
  • A later reply humorously reiterates the clarification while adding a light-hearted note about the context in which the computation might be done.

Areas of Agreement / Disagreement

Participants generally agree on the definition of 'tr' as 'trace', but the initial confusion about the term indicates some misunderstanding that remains unresolved.

Contextual Notes

The discussion does not address the underlying mathematical principles or assumptions related to the trace operation or the derivation itself.

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Hey I am currently studying Quantum Mechanics and I have difficulty grasping a concept.

I don't understand the following step in the derivation:

[itex]\langle X_{A} \rangle=tr\left[\left(X_{A}\otimes I_{B}\right)\rho_{AB}\right][/itex]
[itex]=tr_{A}\left[X_{A} tr_{B}\left[\rho_{AB}\right]\right][/itex]

Thanks
 
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I believe 'tr' stands for 'trace', not 'trance'.
 
yes of course
 
SteamKing said:
I believe 'tr' stands for 'trace', not 'trance'.

Note if you're computing it while listening to techno music :).
 

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