create quantum_fourier_transform

quantum/q_fourier_transform.py

@@ -0,0 +1,63 @@
+"""
+Build the quantum fourier transform (qft) for a desire
+number of quantum bits using Qiskit framework. This
+experiment run in IBM Q simulator with 10000 shots.
+This circuit can be use as a building block to design
+the Shor's algorithm in quantum computing. As well as,
+quantum phase estimation among others.
+.
+References:
+https://en.wikipedia.org/wiki/Quantum_Fourier_transform
+https://qiskit.org/textbook/ch-algorithms/quantum-fourier-transform.html
+"""
+
+import qiskit
+from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister, execute, Aer
+import numpy as np
+
+def qft(n: int = 3) -> qiskit.result.counts.Counts:
+    """
+    # >>> qft(qbits_number)
+    # ideally "shots/2**qbits" counts for each state.
+    # For the default case (n=3) the average is 1250 for
+    # each quantum state.
+                                               ┌───┐   
+    qr_0: ──────■──────────────────────■───────┤ H ├─X─
+                │                ┌───┐ │P(π/2) └───┘ │ 
+    qr_1: ──────┼────────■───────┤ H ├─■─────────────┼─
+          ┌───┐ │P(π/4)  │P(π/2) └───┘               │ 
+    qr_2: ┤ H ├─■────────■───────────────────────────X─
+          └───┘                                        
+    cr: 3/═════════════════════════════════════════════
+    Args:
+        n : number of qubits
+    Returns:
+        qiskit.result.counts.Counts: Counts for each state.
+    """
+    qr = QuantumRegister(n, 'qr')
+    cr = ClassicalRegister(n, 'cr')
+
+    quantum_circuit = QuantumCircuit(qr, cr)
+
+    counter = n
+    # Add the hadamard gates and the CROT gates.
+    for i in range(counter):
+
+        quantum_circuit.h(n-i-1)
+        counter = counter-1
+        for j in range(counter):
+            quantum_circuit.cp(np.pi/2**(counter-j), j, counter)
+
+    for k in range(n//2):
+        quantum_circuit.swap(k, n-k-1)
+
+    # measure all the qubits
+    quantum_circuit.measure(qr,cr)
+    # simulate with 10000 shots
+    backend = Aer.get_backend('qasm_simulator')
+    job = execute(quantum_circuit,backend, shots = 10000)
+
+    return job.result().get_counts(quantum_circuit)
+
+if __name__ == "__main__":
+    print(f"Total count for qft state is: {qft(3)}")