Canonical Commutation Relation Explained?

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Discussion Overview

The discussion revolves around the canonical commutation relation, particularly in the context of Pauli matrices and their properties in quantum mechanics. Participants seek a thorough understanding of the topic, including references for further reading and specific mathematical expressions involving the matrices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses a desire for comprehensive information on the canonical commutation relation and requests resources for further reading.
  • Another participant provides a mathematical expression involving Pauli matrices and notes that it results in a four by four matrix dependent on the indices.
  • There is a suggestion that the trace of the expression might be of interest, as it can be simplified more easily than the original matrix expression.
  • A participant discusses the trace of a product of sigma matrices and suggests using anti-commutation relations and the cyclic property of the trace to derive relationships between traces of different combinations of sigma matrices.
  • There is a question about the identity related to the trace of four sigma matrices, prompting further exploration of the mathematical properties involved.

Areas of Agreement / Disagreement

The discussion does not reach a consensus, as participants express varying levels of understanding and interest in different aspects of the topic, particularly regarding the mathematical simplifications and the resources for learning more.

Contextual Notes

Participants reference specific mathematical properties and relationships without fully resolving the details of the calculations or assumptions involved in the trace operations and commutation relations.

Who May Find This Useful

This discussion may be useful for students or individuals interested in quantum mechanics, particularly those looking to understand the properties of Pauli matrices and their applications in quantum theory.

ice109
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what is it? i need to know everything about it. i know it encompasses a lot of different stuff but yea if someone could point me to a book or webpage that explains it thoroughly.

additionally what does this equal

\sigma_{\mu}\sigma_{\alpha}\sigma_{\alpha}\sigma_{\mu}

those are pauli matrices btw. alpha is just an arbitrary index to differentiate it from the \mu index
 
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anyone?
 
ice109 said:
...
additionally what does this equal

\sigma_{\mu}\sigma_{\alpha}\sigma_{\alpha}\sigma_{\mu}

some four by four matrix that depends on all the indices. The expression doesn't get any simpler than that... are you sure you don't maybe want the value of the trace? that is easily simplified.
 
ice109 said:
what is it? i need to know everything about it. i know it encompasses a lot of different stuff but yea if someone could point me to a book or webpage that explains it thoroughly.

...probably any QM book. Try Messiah's book.
 
olgranpappy said:
some four by four matrix that depends on all the indices. The expression doesn't get any simpler than that... are you sure you don't maybe want the value of the trace? that is easily simplified.

what's the identity?
 
ice109 said:
what's the identity?

You mean, you want to know the RHS of the equation
<br /> Tr(\sigma_\alpha\sigma_\beta\sigma_\gamma\sigma_\delta)=?<br />

You can figure it out by commuting one of the sigma matrices on the far left all the way to the right (using the *anti*commutation relations for sigma matrices) and then using the cyclic property of the trace to get it back. This gives you an equation for the trace of four sigma matrices in terms of the trace of two sigma matrices. The trace of two sigma matrices can be then figured out in the same way. E.g.
<br /> Tr(\sigma_i \sigma_j)=Tr(-\sigma_i\sigma_j+2\delta_{ij})=-Tr(\sigma_i\sigma_j)+4<br />
 

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