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The quantum mechanical time evolution operator governs how observables and/or states evolve during finite time steps, and is always unitary. Use this tag for questions about the time evolution operator, or the different equations of motion in the Schrödinger/Heisenberg/Dirac pictures. For time-independent Hamiltonians, the time evolution operator is simply exp(-iHt).

3 votes
1 answer
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Form of the interaction representation time evolution operator

I am a bit confused about the interaction representation picture. Consider the time independent Hamiltonian $H = H_0 + V$. My question concerns the interaction representation time evolution operator: …
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0 votes
1 answer
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The Adiabatic Theorem and Symmetries of the Hamiltonian

For this question, all operators and states are on a finite dimensional Hilbert space. Suppose I have a collection of continuously parametrized Hamiltonians $H(t), 0\leq t\leq T$. Suppose furthermore …
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Is this proof of Griffith's watertight?

He does not say that $\Psi(x, t)$ must be normalized; he says it must be normalizable, meaning that $$\int_{-\infty}^{\infty} |\Psi(x, t)|^2\text{d}t < \infty.$$ It is easy to see why $\Psi(x, t)$ mus …
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9 votes
3 answers
2k views

Why is imaginary time evolution non-unitary?

If I have a Hamiltonian $H$, the corresponding time-evolution operator is $e^{-iHt}$. If one defines the evolution operator in imaginary time, one uses $e^{-H\tau}$, where $\tau = it$. It is commonly …
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