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CQs: Precession of Spin-1/2 in B-Field

September 25, 2016

This week we started look at time evolution in quantum mechanics. Since this is a spins-first approach, that we means we first take a look at the spin-1/2 particle in a uniform magnetic field.

Here are clicker questions from our day looking at this:

  1. This first question was asked after setting up the problem, but before getting into QM. Take in a moment to make sure we understand the classical perspective.

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2. This question was asked after having worked through the time evolution, and have an expression for the state as a function of time. Good time to re-emphasize the significance of an overall phase change and the idea of energy eigenstates as being stationary.

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3. This question was asked after changing the initial state to be a superposition of energy eigenstates. In talking through this question, we both “cranked out the calculations”, but spent a fair amount of time sense-making about precession in the x-y plane.

screen-shot-2016-09-25-at-8-33-03-am

This last question, brought us back to physically sense making and to take in the big picture, rather than sense-making about a particular mathematical expression or result.

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