How does QM explain that we see electrons circulating in a magnetic field?

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SUMMARY

This discussion focuses on the quantum mechanical (QM) explanation of electron behavior in a magnetic field, particularly addressing the classical circular motion of electrons and the concept of angular momentum quantization. Participants highlight the use of Hamiltonians, specifically the form \( H = \frac{1}{2m}(\mathbf{p} - q \mathbf{A})^2 \), to describe the dynamics of charged particles in a magnetic field. The discussion also emphasizes the significance of the Ehrenfest theorem in relating quantum expectations to classical forces, ultimately clarifying the connection between quantum mechanics and classical physics through Landau levels and wavepacket behavior.

PREREQUISITES
  • Quantum Mechanics fundamentals, including wavefunctions and operators
  • Understanding of Hamiltonian mechanics, particularly in the context of electromagnetic fields
  • Familiarity with the Ehrenfest theorem and its implications in quantum systems
  • Knowledge of Landau levels and their role in quantum systems under magnetic fields
NEXT STEPS
  • Study the derivation and implications of the Ehrenfest theorem in quantum mechanics
  • Explore the concept of Landau levels and their significance in quantum physics
  • Learn about the Hamiltonian formulation for charged particles in electromagnetic fields
  • Investigate the differences between canonical momentum and kinetic momentum in quantum systems
USEFUL FOR

This discussion is beneficial for physicists, particularly those specializing in quantum mechanics, electromagnetism, and anyone interested in the intersection of classical and quantum physics, especially in the context of charged particles in magnetic fields.

  • #31
Heidi said:
I do not see how to visualize latex formulas in this forum.

See "Delimiting your LaTeX code" in Physics Forums help for LaTeX,

https://www.physicsforums.com/help/latexhelp/
 
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  • #32
If you're not sure how to evaluate the energy from the Hamiltonian ##H = \hbar \omega (a^\dagger a + \frac{1}{2})##, then you may want to review the harmonic oscillator in the ladder operator picture. It's discussed in pretty much any serious quantum textbook, undergraduate or graduate level. Griffiths (2nd Ed.) section 2.3.1 is a good place to start. (You can later derive the coherent states step-by-step with hints in Problem 3.35.)

Heidi said:
there are also the formulas in the Landau book. n and m are definite and i read
E = hbar omega (n + m + 1/2)

are they talking about the same energy?
Yes, just in terms of quantum numbers that describe different basis states (sounds like eigenmodes in cartesian coordinates?). The energies are always the same, in any basis and any gauge. If you're quoting a result from Landau, please share which volume and section you are reading from so we can see what you're looking at.
 
  • #33
It is in vol 3 quantum mechanics (non relativistic)
chapter xv motion in a magetic field . problem 1 page 460
we have E depending on n and m and it is written that it is equivalent to 112.7 where there is no m.
we have here |m| + m which is null if m négative but is it so here?
 
  • #34
j bought the first part of the paper written by Kuo-Ho Yang . Thank you VanHees71. I ignored that an hamiltonian could be cut in 2 parts. A "basis" part with a basis of orthonormal eigenvectors and a residual part. Here the résidual part is omega times Lz i suppose.
 

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