Weak time-dependent transition amplitudes
Starting in eigenstate i of fixed H₀, a weak perturbation V(t) gives first-order amplitude c_f(t)=−(i/ħ)∫_{t₀}^t V_fi(t′)exp[i(E_f−E_i)(t′−t₀)/ħ]dt′ for f≠i.
Key knowledge
Starting in eigenstate i of fixed H₀, a weak perturbation V(t) gives first-order amplitude c_f(t)=−(i/ħ)∫_{t₀}^t V_fi(t′)exp[i(E_f−E_i)(t′−t₀)/ħ]dt′ for f≠i. The leading transition probability is |c_f|².
Values and equations
c_f^(1)=−(i/ħ)∫ V_fi(t′)e^[i(E_f−E_i)(t′−t₀)/ħ]dt′; P_i→f≈|c_f^(1)|²
- V_fi,E_f,E_i
- Perturbation matrix element and eigenenergies J
- t,t′,t₀
- Times s
- ħ
- Reduced Planck constant J s
- c_f,P_i→f
- Dimensionless amplitude/probability
- i
- Imaginary unit or initial-state index as context specifies
Conditions and scope
- Orthonormal eigenbasis and perturbative regime with small transition probabilities; evaluate matrix elements in the unperturbed basis.
- Long resonant evolution can invalidate first order; normalization and depletion need higher order or an exact model.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Richard Fitzpatrick / University of Texas at Austin2 sources
Evidence and review
Quantum Mechanics (2016): General analysis: Equations 8.6–8.12: exact coefficient evolution; first-order expression obtained by retaining the initial coefficient in the integrand. Quantum Mechanics (2010): Harmonic perturbations: Equations 1067–1071: first-order integral and energy-frequency phase.
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Entry details
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