Energy of a state of a hydrogenic atom

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SUMMARY

The energy of a He+ atom in the pure state |1,0,0> can be calculated using the formula E_{|n,l,m>} = -\frac{m_e Z^2 e^4}{2\hbar^2} \frac{1}{n^2}, where Z=2 for the He+ ion. For the mixed state |si> = [1/(3^1/2)][2^1/2|2,1,0> + |2,1,-1>, the expectation values , , and must be calculated at t=0. The raising and lowering operators, L+ and L-, are essential for expressing Lx, which can be derived from the relationship \hat{L}_\pm = \hat{L}_x \pm i\hat{L}_y.

PREREQUISITES
  • Understanding of quantum mechanics principles, specifically hydrogenic atom models.
  • Familiarity with angular momentum operators in quantum mechanics.
  • Knowledge of expectation values in quantum states.
  • Proficiency in mathematical expressions involving complex numbers and operators.
NEXT STEPS
  • Study the derivation of energy levels for hydrogen-like atoms, focusing on the He+ ion.
  • Learn about the application of raising and lowering operators in quantum mechanics.
  • Research how to compute expectation values for mixed quantum states.
  • Explore the mathematical properties of angular momentum operators, particularly Lx, Ly, and Lz.
USEFUL FOR

Students and professionals in quantum mechanics, physicists working with atomic models, and anyone studying the properties of hydrogenic atoms and angular momentum in quantum systems.

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Homework Statement


One of a He+ atom is in a pure state |1,0,0>. What is the energy of this state? Give a numerical answer in eV. Another of these is found to be in a mixed state: |si>=[1/(3^1/2)][2^1/2|2,1,0>+|2,1,-1>. Calculate the following expectation values at t=0; <E>,<Lz>,<Lx> HINT: start by writing Lx in terms of the raising and lowering operators, L+ and L-

Homework Equations


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The Attempt at a Solution


I think I'm supposed to calculate the ground state? I'm not sure what formula to use.
 
Last edited:
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The He+ ion behaves like a hydrogen atom with double-charged nucleus (Z=2). Hence the corresponding expression for hydrogen energy levels can be used.

Relevant equations:

<br /> E_{|n,l,m&gt;} = -\frac{m_e Z^2 e^4}{2\hbar^2} \frac{1}{n^2}<br />

<br /> \hat{L}_\pm = \hat{L}_x \pm i\hat{L}_y<br />
 
Ok, so I found the energy, <E>, and <Lz>, but how do I determine <Lx>? I tried writing it in terms of L+-, but I ended up just proving the equation true or having to deal with Ly. I need to know what Lx|n,l,m> is, but I can't figure it out!
 
Last edited:

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