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What is the Hadamard gate?
The Hadamard gate is a single-qubit quantum gate that turns a qubit in |0⟩ into an equal superposition of 0 and 1.
H maps |0⟩ to (|0⟩+|1⟩)/√2 and |1⟩ to (|0⟩−|1⟩)/√2. Both states give 50–50 results on measurement; they differ only in sign, which shows up only through interference.
H is its own inverse: applied twice, it returns the qubit to its starting state. Almost every quantum algorithm starts with H gates to put qubits into superposition.
Try it yourself
The lesson Superposition: a mixture of 0 and 1 lets you try this concept in the browser, with no installation.
Related packages
Related concepts
- Superposition · Superposition is the quantum state in which a qubit, before it is measured, holds the states 0 and 1 together with definite amplitudes.
- Quantum interference · Quantum interference is the way amplitudes add up like waves, raising the probability of some results and cancelling others to zero.
- Quantum gate · A quantum gate is a basic operation that reversibly changes the state of one or more qubits; quantum programs are sequences of gates.