 Solution

ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2019/paper-2/section-a-ii/15/iv/c/solution

The measured energy selects

n = 3

. Immediately after an ideal projective measurement, the normalized state is $ψ_{3} (x)$ up to an overall phase, with no surviving

n = 1, 2, 4

components. At later times before any further disturbance it is

e^{- i 9 c (t - t_{0}) /ℏ} ψ_{3} (x)

, where

t_{0}

is the measurement time. A repeated energy measurement returns $9 c$ with probability one.

 New to topics? Read the docs here!