Quantum Full adder

4-Bit Quantum Full Adder circuit implemented to perform the addition of two 4-bit numbers using Quantum Circuits, using only C-NOT & Tofolli gates in Python/Qiskit for certain test cases:



The circuit implemented is as follows: this circuit is a single-bit Quantum Full Adder circuit & in my implementation, it is constructed 4 times to augment 4-bit functionality & barriers have been created to separate single full adder circuits & at last measurements of the obtained sum & final carry bit have been taken.

computation of the sum and carry bits are done using the following relations:


Some more gate combinations (X[NOT], H[Hadamard] & CX[CNOT]) were also appended before the full adder circuit to initialize the qubit states (A and B) to that of the test cases (some were superimposed, some were pure)

Measurements were taken, and the probability of output states was measured as well a histogram plot was drawn for the measurements using Quantum Simulator (QASM)

Credits:
https://www.researchgate.net/publication/346508632/figure/fig1/AS:963729009156096@1606782309965/Circuit-model-of-a-quantum-full-adder.png
https://qiskit.org/documentation/
https://www.geeksforgeeks.org/full-adder-in-digital-logic/