Classical bit vs qubit
Distinguish a stored bit from a quantum state and a measurement outcome.
Intuition
A classical bit has value 0 or 1. A qubit is described by a quantum state. Measuring it in the computational basis still gives just one bit: 0 or 1.
A superposition is not a way to read two answers at once. Quantum computations change amplitudes so that interference changes which outcomes are likely. Start with a definite state before exploring superposition.
The mathematics
Look a little deeper
These column vectors are an orthonormal basis for a two-dimensional complex vector space. Their entries are amplitudes, not the two possible results of a single measurement.
Use it
Start at |0⟩. Use one X gate to make measurement return 1 with certainty.
This exercise uses the same server-side state and circuit checks as its linked practice problem.
Build your circuit
Click a gate to append it, or drag it onto a wire. CX uses the selected control; SWAP uses it as the second operand. Basis order: |qₙ … q₀⟩.
Returned logical circuit · before transpilation · q0 on top
Connect to code
qc = QuantumCircuit(1) qc.x(0)
These operations go inside a circuit-building program. Practice problems provide a complete solve() template.
Check your understanding
First complete the circuit exercise successfully.