See what a qubit looks like before you measure it
What does a qubit look like before you measure it?
A qubit always starts in the |0⟩ state, which you can think of as a coin sitting heads-up on a table. In this experiment you will apply a single gate called the Hadamard (H) that puts the qubit into an equal mix of |0⟩ and |1⟩. This mixed state is called superposition.
Before measurement, a qubit in superposition is not secretly 0 or secretly 1. It genuinely holds both possibilities at once, each with a probability amplitude. The Hadamard gate creates this by splitting the |0⟩ state into two equal branches. When you finally measure, each branch has a 50% chance of being the outcome you see. Run the experiment many times and watch the histogram settle toward a balanced split.
The H gate transforms |0⟩ into an equal superposition of |0⟩ and |1⟩. Watch the Bloch sphere: the arrow moves from the north pole (pure |0⟩) to the equator, where it points along the +X direction. The histogram now shows equal weight on both outcomes.
It is tempting to think superposition means the qubit reads out both 0 and 1 at the same time. That is not what happens. Each measurement returns one ordinary classical outcome. Superposition describes the probabilities before measurement, not the result after it.
The active qubit produces 0 and 1 with roughly equal frequency. Over 1000 shots you should see counts near 500 for each outcome. Any untouched qubits stay in |0⟩.
This experiment is a hands-on companion to the Superposition and Measurement lesson. That lesson explains the mathematical framework (amplitudes, Born rule, state vectors) behind what you see here. After running this experiment, the formula |+⟩ = (|0⟩+|1⟩)/√2 should feel concrete rather than abstract.
Read the full lesson →After applying H to |0⟩, you run a single measurement. What do you see?