Curriculum / Quantum Gates Deep Dive / Gates Capstone, 3-Qubit GHZ State
Gates Capstone, 3-Qubit GHZ State
Apply everything: build the 3-qubit GHZ state from scratch.
Gates Capstone, 3-Qubit GHZ State
The GHZ (Greenberger-Horne-Zeilinger) state is the 3-qubit generalization of the Bell state:
|GHZ⟩ = (|000⟩ + |111⟩)/√2
It's a maximally entangled 3-qubit state with profound implications for quantum communication, quantum error correction, and tests of quantum mechanics.
Building GHZ
The circuit uses everything you've learned:
- 1.H on qubit 0 (superposition)
- 2.CNOT(0,1) (entangle qubit 1)
- 3.CNOT(0,2) (entangle qubit 2)
Result: (|000⟩ + |111⟩)/√2, all three qubits are correlated.
Properties of GHZ
Measure any one qubit: get 0 or 1 with 50/50 probability. But all three qubits always agree, you'll only ever see 000 or 111.
This violates local realism even more strongly than Bell states.
Your Challenge
Build the GHZ state with 3 qubits. Verify only 000 and 111 appear.
How this lesson works
A hands-on coding challenge. You write Qiskit-compatible Python in the browser editor, run it instantly via WebAssembly, watch the circuit and Bloch sphere react, and pass automatic output checks. The AI tutor Qubitus gives Socratic hints if you get stuck.
Part of: Quantum Gates Deep Dive
Master single-qubit and multi-qubit gates. Understand rotations, phases, and the math behind every gate in Qiskit.
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