Solution

ID: past-exam-of-the-short-options-paper-shared-by-prelims-and-parts-a-and-b-of-the-physics-course-of-the-university-of-oxford/2018/s3/2/a/solution

Choose the overall phase so that is positive. Normalization requires
Therefore
An arbitrary constant phase multiplying this answer has no effect on any expectation value.

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