Bell states are the four maximally entangled two-qubit quantum states. They serve as the foundation for quantum teleportation, superdense coding, and many quantum protocols.

The Four Bell States

|Φ⁺⟩ = (|00⟩ + |11⟩)/√2 |Φ⁻⟩ = (|00⟩ - |11⟩)/√2 |Ψ⁺⟩ = (|01⟩ + |10⟩)/√2 |Ψ⁻⟩ = (|01⟩ - |10⟩)/√2

Creating Bell States

A Bell state is created by applying a Hadamard gate to the first qubit, followed by a CNOT gate with the first qubit as control and the second as target.

Why Entanglement Matters

Entangled qubits exhibit correlations that cannot be explained by classical physics. Measuring one qubit instantly determines the state of the other, regardless of distance — a phenomenon Einstein called 'spooky action at a distance'.