Quick Start

Let’s build a Bell state: two qubits entangled so that measuring one instantly tells you the other.

The circuit

from fqkit import QuantumCircuit, Hadamard, CNOT, run, measure_all
 
qc = QuantumCircuit(2)
qc.add_gate(Hadamard(), [0])   # put qubit 0 into superposition
qc.add_gate(CNOT(), [0, 1])    # entangle qubit 1 with qubit 0
 
state = run(qc)
counts = measure_all(state, shots=1024)
 
print("State :", state)
print("Counts:", counts)

What happens

1. Hadamard() puts qubit 0 into an equal superposition of |0> and |1>.
2. CNOT() uses qubit 0 as the control and qubit 1 as the target, so the two qubits become correlated.
3. run(qc) simulates the circuit and returns the final statevector.
4. measure_all(state, shots=1024) samples the state 1024 times.

Output

State : [0.70710678+0.j 0.+0.j 0.+0.j 0.70710678+0.j]
Counts: {'00': 512, '11': 512}

The state is (|00> + |11>) / sqrt(2): the circuit only ever produces 00 or 11, never 01 or 10. That correlation is entanglement.

Next steps

• Learn about the gate library
• Understand simulation & measurement
• Export your circuit to OpenQASM
• Submit it to a real machine