Energy release/gain in superposition (in Stern-Gerlach) Let's have a quantum system in superpositon of two states $|e>$ and |g> with coefficients a and b. Now the system interracts with a field and is projected on either |e> or|g>. The question is what energy does the system release or accept and where gets it from?
An example is the Stern Gerlach experiment. The electron is projected in spin up or down. But what energy it releases going from $a|e>+b|g>->|g>$ and where it takes it from (if from the magnet - what happens with its domains and what it apply for photons being involved as carriers from a pure magnetic field to an electron? 
 A: In quantum mechanics, you can prepare your state in superpositions of energy, and measurements can collapse your state and change its energy. 
In a lab, I can prepare a photon to be in superposition state of $(|0\rangle + |1\rangle)\frac{1}{\sqrt{2}}$. Which means that, if I were to measure my state with a detector, half of the time I have a photon, and half of the time I don't. 
One "conservation law" that remains the same with clasical mechanics is that the expected value of the energy will stay the same. So for example in our photon detection experiment, the expected value of the energy is 1/2 the energy of a photon, and this is what we will measure since half the time we'll measure 0 and half the time we will measure energy of a photon. (This works in the cases that I can think of, although there might be some experiements where some tricks are done to voilate this).
Sometimes this is "measurement collapses energy wavefunction" feature of quantum mechanics is exploited. For instance, in the quantum zeno effect you can show that simply by constantly making measurements frequently, you can force a state to not evolve in time and remain "locked" in a particular state forever! 
