Quantum Mechanics: Concepts and Applications · Problem 3.2

Postulates of Quantum Mechanics — Nouredine Zettili

Physics — Quantum Mechanics · probability-superposition-principle

Problem

Consider a system whose state is given in terms of an orthonormal set of three vectors: ∣ϕ1⟩|\phi_1\rangle, ∣ϕ2⟩|\phi_2\rangle, ∣ϕ3⟩|\phi_3\rangle as ∣ψ⟩=33∣ϕ1⟩+23∣ϕ2⟩+23∣ϕ3⟩|\psi\rangle = \frac{\sqrt{3}}{3}|\phi_1\rangle + \frac{2}{3}|\phi_2\rangle + \frac{\sqrt{2}}{3}|\phi_3\rangle (a) Verify that ∣ψ⟩|\psi\rangle is normalized. Then, calculate the probability of finding the system in any one of the states ∣ϕ1⟩|\phi_1\rangle, ∣ϕ2⟩|\phi_2\rangle, and ∣ϕ3⟩|\phi_3\rangle. Verify that the total probability is equal to one. (b) Consider now an ensemble of 810 identical systems, each one of them in the state ∣ψ⟩|\psi\rangle. If measurements are done on all of them, how many systems will be found in each of the states ∣ϕ1⟩|\phi_1\rangle, ∣ϕ2⟩|\phi_2\rangle, and ∣ϕ3⟩|\phi_3\rangle?

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