Can somebody tell me what a qubit actually is? In classical electronics a bit is, in theory, a piece of information that is in a state of either 1 or 0 while, in practice, it is a voltage level of a conductor which is above or below a certain threshold (generally far above or below, at the supply rails, for signal integrity's sake, but there are applications especially in high speed electronics where it can be fairly tight). When reading into quantum computing, there seems to be plenty of description of the theory but what is it in practice? An electron with a different spin state? Photons?
