Superposition
Beginner · 5 lessons · 18 activities
A qubit's state is two signed numbers, not one unknown bit. Read them off the Bloch circle, write them as a|0⟩ + b|1⟩ with |a|² + |b|² = 1, and run the experiment that tells a superposition apart from a coin flip nobody has looked at.
Lessons
What a superposition is
Two signed amplitudes, drawn on the Bloch circle and written as a linear combination. Build one yourself, then run the experiment that separates it from a coin flip nobody has looked at.
5 activities · 14 min
Writing a state down
The notation, once there is something to write with it. Why the brackets, why a column of two numbers, and why two levels is not two places.
4 activities · 11 min
Making a superposition
Build the quantum coin: prepare the state, measure it, and see why one run tells you almost nothing while a thousand tell you the amplitudes.
4 activities · 12 min
Not a coin nobody looked at
The sharpest difference between a superposition and ordinary ignorance: you can undo a superposition exactly, and you cannot un-flip a coin.
4 activities · 12 min
Proficiency challenge
Three stages against the clock: read a state, predict its sampled counts, and separate a superposition from a mixture.
1 activity · 6 min