circuit.py

# Name: circuit.py
# Author: Isaac Cilia Attard
# Date: 04/10/2022
# Description: Implements the QFT circuit as detailed in the README.

"""NumPy packages"""
import numpy as np
from numpy import pi
"""Qiskit package"""
from qiskit import QuantumCircuit

def rotations(quantum_circuit, n): # Installs necessary rotation gates onto an empty circuit
    if n == 0: # Returns finalised generated circuit upon meeting the last qubit
        return quantum_circuit
    n -= 1 # Decrements current qubit to continue generating circuit
    """Generates gates for QFT"""
    quantum_circuit.h(n) # Hadamard gate application
    for qubit in range(n):
        quantum_circuit.cp(pi/2**(n-qubit), qubit, n) # Controlled-phase gate application
    rotations(quantum_circuit, n) # Utilises recursion to rotate the rest of the n-1 qubits

def swap(quantum_circuit, n): # Swaps qubits in order to match QFT definition
    for qubit in range(n//2):
        quantum_circuit.swap(qubit, n-qubit-1)
    return quantum_circuit

def qft(quantum_circuit, n): # Generalised QFT-circuit generator based on mathematical derivation
    """Generation is split into two functions"""
    rotations(quantum_circuit, n)
    swap(quantum_circuit, n)
    return quantum_circuit # Returns finalised circuit