J

T

R

```
# https://github.com/rupansh/QuantumComputing/blob/master/rippleadd.py
# https://en.wikipedia.org/wiki/Adder_(electronics)#Full_adder
# https://en.wikipedia.org/wiki/Controlled_NOT_gate
import qiskit
from qiskit.providers import Backend
def store_two_classics(val1: int, val2: int) -> tuple[qiskit.QuantumCircuit, str, str]:
"""
Generates a Quantum Circuit which stores two classical integers
Returns the circuit and binary representation of the integers
"""
x, y = bin(val1)[2:], bin(val2)[2:] # Remove leading '0b'
# Ensure that both strings are of the same length
if len(x) > len(y):
y = y.zfill(len(x))
else:
x = x.zfill(len(y))
# We need (3 * number of bits in the larger number)+1 qBits
# The second parameter is the number of classical registers, to measure the result
circuit = qiskit.QuantumCircuit((len(x) * 3) + 1, len(x) + 1)
# We are essentially "not-ing" the bits that are 1
# Reversed because it's easier to perform ops on more significant bits
for i in range(len(x)):
if x[::-1][i] == "1":
circuit.x(i)
for j in range(len(y)):
if y[::-1][j] == "1":
circuit.x(len(x) + j)
return circuit, x, y
def full_adder(
circuit: qiskit.QuantumCircuit,
input1_loc: int,
input2_loc: int,
carry_in: int,
carry_out: int,
):
"""
Quantum Equivalent of a Full Adder Circuit
CX/CCX is like 2-way/3-way XOR
"""
circuit.ccx(input1_loc, input2_loc, carry_out)
circuit.cx(input1_loc, input2_loc)
circuit.ccx(input2_loc, carry_in, carry_out)
circuit.cx(input2_loc, carry_in)
circuit.cx(input1_loc, input2_loc)
# The default value for **backend** is the result of a function call which is not
# normally recommended and causes flake8-bugbear to raise a B008 error. However,
# in this case, this is acceptable because `Aer.get_backend()` is called when the
# function is defined and that same backend is then reused for all function calls.
def ripple_adder(
val1: int,
val2: int,
backend: Backend = qiskit.Aer.get_backend("aer_simulator"), # noqa: B008
) -> int:
"""
Quantum Equivalent of a Ripple Adder Circuit
Uses qasm_simulator backend by default
Currently only adds 'emulated' Classical Bits
but nothing prevents us from doing this with hadamard'd bits :)
Only supports adding positive integers
>>> ripple_adder(3, 4)
7
>>> ripple_adder(10, 4)
14
>>> ripple_adder(-1, 10)
Traceback (most recent call last):
...
ValueError: Both Integers must be positive!
"""
if val1 < 0 or val2 < 0:
raise ValueError("Both Integers must be positive!")
# Store the Integers
circuit, x, y = store_two_classics(val1, val2)
"""
We are essentially using each bit of x & y respectively as full_adder's input
the carry_input is used from the previous circuit (for circuit num > 1)
the carry_out is just below carry_input because
it will be essentially the carry_input for the next full_adder
"""
for i in range(len(x)):
full_adder(circuit, i, len(x) + i, len(x) + len(y) + i, len(x) + len(y) + i + 1)
circuit.barrier() # Optional, just for aesthetics
# Measure the resultant qBits
for i in range(len(x) + 1):
circuit.measure([(len(x) * 2) + i], [i])
res = qiskit.execute(circuit, backend, shots=1).result()
# The result is in binary. Convert it back to int
return int(list(res.get_counts())[0], 2)
if __name__ == "__main__":
import doctest
doctest.testmod()
```