01 · Units

Bit

A fair coin is 1 bit of uncertainty. A two-level atom, unmeasured, is a qubit — more than a bit, until you look, and then it is a bit again.

In English

A bit is not a hard drive. It is the surprise of a fair yes/no. A biased coin is less than one bit — you already half-know. A qubit, before you look, is a richer object; after you look, you have a bit again.

Try this: Flip the fair coin. That was one bit. Then bias it: each flip should feel less informative.
Keep this: One fair yes/no = one bit. Bias shrinks it.

Lab · one fair bit

Two equally likely outcomes. You cannot compress a fair flip: the answer is 1 bit, every time.

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Not yet flipped

Shannon’s bit is a fair binary choice. It is a unit of uncertainty, not a transistor. Hardware bits store one of these after a decision has been made.

A qubit is a different object. Measuring it produces a bit and destroys the rest. Volume II; this volume is the bill you pay after.