Python/quantum/half_adder.py

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#!/usr/bin/env python3
"""
Build a half-adder quantum circuit that takes two bits as input,
encodes them into qubits, then runs the half-adder circuit calculating
the sum and carry qubits, observed over 1000 runs of the experiment
.
References:
https://en.wikipedia.org/wiki/Adder_(electronics)
https://qiskit.org/textbook/ch-states/atoms-computation.html#4.2-Remembering-how-to-add-
"""
import qiskit
def half_adder(bit0: int, bit1: int) -> qiskit.result.counts.Counts:
"""
>>> half_adder(0, 0)
{'00': 1000}
>>> half_adder(0, 1)
{'01': 1000}
>>> half_adder(1, 0)
{'01': 1000}
>>> half_adder(1, 1)
{'10': 1000}
"""
# Use Aer's simulator
simulator = qiskit.Aer.get_backend("aer_simulator")
qc_ha = qiskit.QuantumCircuit(4, 2)
# encode inputs in qubits 0 and 1
if bit0 == 1:
qc_ha.x(0)
if bit1 == 1:
qc_ha.x(1)
qc_ha.barrier()
# use cnots to write XOR of the inputs on qubit2
qc_ha.cx(0, 2)
qc_ha.cx(1, 2)
# use ccx / toffoli gate to write AND of the inputs on qubit3
qc_ha.ccx(0, 1, 3)
qc_ha.barrier()
# extract outputs
qc_ha.measure(2, 0) # extract XOR value
qc_ha.measure(3, 1) # extract AND value
# Execute the circuit on the qasm simulator
job = qiskit.execute(qc_ha, simulator, shots=1000)
# Return the histogram data of the results of the experiment
return job.result().get_counts(qc_ha)
if __name__ == "__main__":
counts = half_adder(1, 1)
print(f"Half Adder Output Qubit Counts: {counts}")