Oh, I don't mean to demean the field of Quantum Information. Especially, I find it really useful to run through the double-slit experiment by labelling one slit as |0> and one slit as |1>, and then going through both slits comes out as sqrt(1/2)[ |0> + |1> ] = |+>, which has certain "off-diagonal terms" in its "density matrix."
If all that formalism is built up, you can have fun working through when these off-diagonal terms exist and when they do not, especially in cases where you take a new qubit as |0> and then entangle it into the system with a CNOT gate, where you get |00> + |11>.
It's really kind of rough (in particular I'd like to use proper HTML subscripts rather than Unicode subscripts eventually) but it should be intelligible to a bright student who wants to know the basic ideas of QM.
If all that formalism is built up, you can have fun working through when these off-diagonal terms exist and when they do not, especially in cases where you take a new qubit as |0> and then entangle it into the system with a CNOT gate, where you get |00> + |11>.
If folks are confused by the above, I have begun trying to explain it here: https://github.com/drostie/essay-seeds/blob/master/physics/d...
It's really kind of rough (in particular I'd like to use proper HTML subscripts rather than Unicode subscripts eventually) but it should be intelligible to a bright student who wants to know the basic ideas of QM.