Multi-Qubit Circuits & Entanglement

Build circuits across 2 or 3 qubits, add controlled operations, and inspect entanglement directly through the reduced density matrix, purity, and Schmidt coefficients.

Qubit count

Presets

Wires

Circuit sequence

No operations yet — add gates below.

Add single-qubit gate

qubit

Add multi-qubit gate

control target

Full state — amplitudes

Reading this list. Each row is one basis outcome for all qubits together (e.g. |01⟩ means q0=0, q1=1). The bar shows measurement probability; the value on the right is the complex amplitude behind it.

Entanglement diagnostics

keep qubit (trace out the rest)

ρ = [[1,0],[0,0]]

Purity Tr(ρ²)1.000

SEPARABLE — no entanglement with the rest of the system

Why purity tells the story. Tr(ρ²) = 1 means this qubit is in a definite pure state on its own. Anything less means it's entangled with the qubits you traced out — the "missing" purity is exactly the information hiding in the correlations.