How to Find the Bloch Vector for a Density Matrix Using Taylor Expansion?

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SUMMARY

The discussion focuses on calculating the Bloch vector for the density matrix \(\frac{1}{N}\exp{-\frac{H}{-k_bT}}\), where the Hamiltonian is defined as \(H=\hbar\omega\sigma_z\). Participants emphasize the importance of breaking the Taylor series of the exponential function into odd and even terms due to the property that \(\sigma_z^2\) equals the identity matrix. The challenge arises from incorporating the imaginary unit \(i\) in Euler's equation to correctly represent the sine and cosine terms derived from the expansion.

PREREQUISITES
  • Understanding of quantum mechanics concepts, specifically Bloch vectors.
  • Familiarity with density matrices and their properties.
  • Knowledge of Taylor series expansions and their applications in quantum mechanics.
  • Basic understanding of Hamiltonians and their role in quantum systems.
NEXT STEPS
  • Study the derivation of Bloch vectors in quantum mechanics.
  • Learn about the properties of density matrices in quantum statistical mechanics.
  • Explore Taylor series expansions and their applications in physics.
  • Investigate the role of the imaginary unit \(i\) in Euler's formula and its implications in quantum mechanics.
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Students and researchers in quantum mechanics, particularly those working with Bloch vectors and density matrices, as well as anyone interested in the mathematical foundations of quantum statistical mechanics.

cscott
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Homework Statement



I need to find the bloch vector for the density matrix \frac{1}{N}\exp{-\frac{H}{-k_bT}} where the Hamiltonian is given by H=\hbar\omega\sigma_z.


The Attempt at a Solution



I can break the Taylor series of exp into odd and even terms because sigma z squared is the identity. I get something that looks like sine and cosine but I'm missing i for Euler's equation. How else can I group the terms?
 
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cscott said:

Homework Statement



I need to find the bloch vector for the density matrix \frac{1}{N}\exp{-\frac{H}{-k_bT}} where the Hamiltonian is given by H=\hbar\omega\sigma_z.


The Attempt at a Solution



I can break the Taylor series of exp into odd and even terms because sigma z squared is the identity. I get something that looks like sine and cosine but I'm missing i for Euler's equation. How else can I group the terms?

I am not going to be very helpful because I know little about Bloch vectors but why do you need to get an i factor? I don't see anything else to do here than to simply expand and get the sine and cos terms.
 
Mmm I think you're right and now I feel stupid :P

Thanks.
 

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