Short Answer
⟨n|H'|n⟩ ≪ Eₙ − Eₙ' is the best answer.
Quantum questions reward precision with language. Identify whether the prompt is about wave behaviour, measurement, states, operators, or quantised energy levels before choosing a formula or interpretation.
Perturbation theory requires the matrix elements of H' to be small compared to the unperturbed energy level spacings.
Why This Answer Is Correct
This is a Hard-level question in Quantum Physics. The prompt is really testing whether you can connect the concept to its defining physical relationship instead of picking a nearby-but-wrong term.
When a quantum question feels ambiguous, translating it into state, observable, probability, and evolution language usually clarifies the answer.
Choices At A Glance
- A. The perturbing Hamiltonian is larger than H₀
- B. ⟨n|H'|n⟩ ≪ Eₙ − Eₙ'
- C. The system is degenerate
- D. Temperature is near absolute zero
When similar options appear on an exam, eliminate the ones that break the core law, use the wrong units, or confuse a definition with a consequence.
Topic Snapshot
Topic: Quantum Physics
Difficulty: Hard
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.