Quantum Circuit Builder

Build a 2-qubit circuit by clicking gates onto each wire. The state vector and measurement probabilities update in real time. Bell state preset is one click away.

State vector

    Amplitudes shown as a + bi. The basis states are |00⟩, |01⟩, |10⟩, |11⟩ (q1 q0).

    Measurement probabilities

    Probability of each outcome if you measure both qubits in the computational basis.

    Export as OpenQASM 3 
     
     
     
     
    How to read the output
     
    
A 2-qubit state lives in a 4-dimensional complex vector space. The four basis states are |00⟩, |01⟩, |10⟩, |11⟩, and any state is a complex superposition of them. The amplitudes you see are those complex coefficients. Squaring each amplitude gives the probability of measuring that bitstring.

     
    
Try the Bell state preset (H on q0, then CNOT q0→q1). You'll see |00⟩ and |11⟩ both at probability 0.5, and |01⟩ and |10⟩ at 0. That's entanglement: the two qubits are perfectly correlated even though neither has a definite value alone.

     
    
For more, see our quantum gates tutorial, the gates cheat sheet, or the single-qubit Bloch sphere simulator.