2. For a certain system the operator corresponding to the physical quantity A does not commute with the Hamiltonian. It has eigenvalues a₁ and a2, corresponding to eigenfunctions: Φι = (u1 + u2) √2 " Φ2 = (u1 - u2) √2 where u1 and U2 are eigenfunctions of the Hamiltonian, with eigenvalues E1 and E2. If the system is in the state =₁ at time t=0, show that the expectation value of A at time t is: (A) = = a1 + a2 + 2 a1 a2 (E1 – E2)t 2 COS h Hints: Remember that the time dependent SE has solutions which include an exponential phase factor exp(-iwt). Start with: (A) = |c₁|²a1 + |c2|2a2 Find the cs by considering the time evolution of the wave function to show that |ci|² == | | 1 [1 + cos(w1 − w2)t] = 2 (eix + e −ix) COST = 2
2. For a certain system the operator corresponding to the physical quantity A does not commute with the Hamiltonian. It has eigenvalues a₁ and a2, corresponding to eigenfunctions: Φι = (u1 + u2) √2 " Φ2 = (u1 - u2) √2 where u1 and U2 are eigenfunctions of the Hamiltonian, with eigenvalues E1 and E2. If the system is in the state =₁ at time t=0, show that the expectation value of A at time t is: (A) = = a1 + a2 + 2 a1 a2 (E1 – E2)t 2 COS h Hints: Remember that the time dependent SE has solutions which include an exponential phase factor exp(-iwt). Start with: (A) = |c₁|²a1 + |c2|2a2 Find the cs by considering the time evolution of the wave function to show that |ci|² == | | 1 [1 + cos(w1 − w2)t] = 2 (eix + e −ix) COST = 2
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