Controlled coherent two-state transition
For two orthonormal states with H₀=diag(E₁,E₂), E₂>E₁, and off-diagonal drive H₁₂=H₂₁*=ħΩ exp(iωt)/2, the initial state |1⟩ has exact probability P₂(t)=Ω² sin²(t√(Ω²+δ²)/2)/(Ω²+δ²), δ=ω−(E₂−E₁)/ħ, and P₁=1−P₂.
Key knowledge
For two orthonormal states with H₀=diag(E₁,E₂), E₂>E₁, and off-diagonal drive H₁₂=H₂₁*=ħΩ exp(iωt)/2, the initial state |1⟩ has exact probability P₂(t)=Ω² sin²(t√(Ω²+δ²)/2)/(Ω²+δ²), δ=ω−(E₂−E₁)/ħ, and P₁=1−P₂. Resonance gives complete periodic transfer for nonzero Ω within this closed model.
Values and equations
H₁₂=H₂₁*=ħΩe^(iωt)/2; δ=ω−(E₂−E₁)/ħ; P₂=Ω²/(Ω²+δ²) sin²[t√(Ω²+δ²)/2]
- H₁₂,E₁,E₂
- Hamiltonian matrix element and undriven energies J
- Ω,ω,δ
- Coupling, drive and detuning angular frequencies rad s⁻¹
- t
- Elapsed time s
- ħ
- Reduced Planck constant J s
- P₁,P₂
- State occupation probabilities
Conditions and scope
- Real fixed Ω and ω; the rotating off-diagonal Hamiltonian and initial state are specified, with no diagonal drive, additional levels or decoherence. For Ω=δ=0 the probability is its continuous limit P₂=0.
- Applying this model to a physical cosine drive generally requires a justified rotating-wave approximation; the exact solution of the specified Hamiltonian does not prove that approximation or a dissipative lifetime model.
Sources · 1
References
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Evidence and review
Quantum Mechanics (2016): Two-state system: Equations 8.13–8.23: Hermitian rotating drive, initial coefficients and squared transition amplitudes. Source γ is renamed Ω; ω₂₁ is the transition angular frequency, not called the Rabi frequency. Misnumbered later equation references are not relied upon.
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Entry details
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