Why people believe this
Superposition lets a qubit be 0 and 1 simultaneously — so it feels natural to think the computer is checking every possible answer in parallel, like running millions of calculations at the same time. Pop science articles repeat this idea constantly.
The correction
Superposition is not parallelism. Yes, a qubit can be in a superposition of states — but the moment you measure the result, the wavefunction collapses to a single classical outcome. If quantum computers truly tried all answers at once, you could just measure and get the right answer immediately. You cannot. The real work in quantum algorithms is engineering interference — carefully arranging the circuit so wrong answers cancel each other out and the correct answer amplitude grows. That is what Grover's algorithm does. That is what makes quantum algorithms hard to design.
Try it in the simulator
What to do
Load the Grover preset. First run it as-is and note the probability distribution — one answer is amplified. Then clear the circuit, place only H gates on both qubits, and simulate — you get equal probabilities. The Grover version amplifies one answer through interference, not by trying all answers.
Research notes
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