I've been following the EdX course on Quantum Computing by Prof. Vazirani and I don't understand how one physically can create a superimposed state of the ground and 1st excited state of an hydrogen atom. He mentions "the use of light," but doesn't explain the frequency of the light, nor the length of the pulse. Can anyone explain this for me? Also, I don't understand the energy considerations when the hydrogen in a superimposed state is measured and found to be in either the ground state or the 1st excited state. Where did the energy either come from (excited state), or disappear (ground state.) ?