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⟨Hf⟩\langle H_f \rangle

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the standard two-level exchange solution, exact for all t under this Hamiltonian. From it, ⟨\langle HSH_S ⟩(t)\rangle(t) = (ℏ\hbarω\omega/2)[cos⁡2(gt)\cos^2(gt) - sin⁡2(gt)\sin^2(gt)] = (ℏ\hbarω\omega/2)cos⁡(2gt)\cos(2gt) , while ⟨\langle HfH_f ⟩\rangle is exactly time-independent — a general fact for any state evolving under its own generator, not special to this one — and equal here to ⟨\langle e,g|HfH_f|e,g⟩\rangle = ℏ\hbarω\omega/2 - ℏ\hbarω\omega/2 + 0 = 0 , since HSBH_{SB} is purely off-diagonal in this basis. The ledger reading follows immediately:

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HfH_f

Symbol H_f

HfH_f is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

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⟨Hf⟩\langle H_f \rangle

Equation 89 · Evolutionary Physics

The Entry a Relabeling Cannot Write

This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text.

the standard two-level exchange solution, exact for all t under this Hamiltonian. From it, ⟨\langle HSH_S ⟩(t)\rangle(t) = (ℏ\hbarω\omega/2)[cos⁡2(gt)\cos^2(gt) - sin⁡2(gt)\sin^2(gt)] = (ℏ\hbarω\omega/2)cos⁡(2gt)\cos(2gt) , while ⟨\langle HfH_f ⟩\rangle is exactly time-independent — a general fact for any state evolving under its own generator, not special to this one — and equal here to ⟨\langle e,g|HfH_f|e,g⟩\rangle = ℏ\hbarω\omega/2 - ℏ\hbarω\omega/2 + 0 = 0 , since HSBH_{SB} is purely off-diagonal in this basis. The ledger reading follows immediately:

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