Probability of staying in same state after time-dep perturbation?

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SUMMARY

The discussion focuses on the probability of a particle remaining in the same energy eigenstate after a time-dependent perturbation, specifically using the particle-in-a-box model. The participant expresses confusion regarding the application of Fermi's Golden Rule, noting that it yields probabilities exceeding 1, which is incorrect. The conversation emphasizes that Fermi's Golden Rule is applicable only for small perturbations and short time intervals, highlighting its limitations in scenarios involving significant perturbations or extended timeframes.

PREREQUISITES
  • Understanding of quantum mechanics principles, particularly energy eigenstates.
  • Familiarity with time-dependent perturbation theory.
  • Knowledge of Fermi's Golden Rule and its applications.
  • Basic grasp of the particle-in-a-box model in quantum mechanics.
NEXT STEPS
  • Study the limitations of Fermi's Golden Rule in quantum mechanics.
  • Explore advanced time-dependent perturbation theory techniques.
  • Investigate alternative methods for calculating probabilities in quantum systems.
  • Review the particle-in-a-box model and its implications in quantum mechanics.
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Students and researchers in quantum mechanics, particularly those studying time-dependent perturbations and their effects on energy eigenstates.

vincebs
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Let's say that you've got a time-dependent perturbation to your potential (say, the particle-in-a-box to make things simple). Say you start in energy eigenstate #3. What's the probability that the particle will stay in eigenstate 3 after time T?

This is not a homework problem. I'm not understanding the equation for the probability which seems to give a number larger than 1.
 
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I take you're staring at Fermi's Golden Rule. That rule is a first order time dependent perturbation result, and so will not give the correct answer at large times or for large perturbations.
 

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