Create qkd.py

quantum/algorithms/qkd.py

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+# qkd.py
+import numpy as np
+from qiskit import QuantumCircuit, Aer, execute
+from qiskit.visualization import plot_histogram
+
+def prepare_qubit(basis, bit):
+    """
+    Prepare a qubit based on the chosen basis and bit value.
+    
+    Parameters:
+    - basis: 'Z' for computational basis, 'X' for Hadamard basis
+    - bit: 0 or 1
+    
+    Returns:
+    - QuantumCircuit: A quantum circuit with the prepared qubit
+    """
+    qc = QuantumCircuit(1, 1)
+    if basis == 'Z':
+        if bit == 1:
+            qc.x(0)  # Prepare |1>
+    elif basis == 'X':
+        if bit == 0:
+            qc.h(0)  # Prepare |+>
+        else:
+            qc.h(0)
+            qc.x(0)  # Prepare |->
+    return qc
+
+def measure_qubit(qc, basis):
+    """
+    Measure the qubit in the specified basis.
+    
+    Parameters:
+    - qc: QuantumCircuit object
+    - basis: 'Z' for computational basis, 'X' for Hadamard basis
+    """
+    if basis == 'Z':
+        qc.measure(0, 0)  # Measure in computational basis
+    elif basis == 'X':
+        qc.h(0)  # Change to computational basis
+        qc.measure(0, 0)
+
+def bb84_protocol(num_bits):
+    """
+    Implement the BB84 Quantum Key Distribution protocol.
+    
+    Parameters:
+    - num_bits: Number of bits to be transmitted
+    
+    Returns:
+    - Alice's key, Bob's key
+    """
+    # Step 1: Alice prepares qubits
+    alice_bits = np.random.randint(0, 2, num_bits)  # Random bits
+    alice_bases = np.random.choice(['Z', 'X'], num_bits)  # Random bases
+    qubits = [prepare_qubit(alice_bases[i], alice_bits[i]) for i in range(num_bits)]
+
+    # Step 2: Bob randomly chooses bases and measures the qubits
+    bob_bases = np.random.choice(['Z', 'X'], num_bits)
+    bob_results = []
+
+    for i in range(num_bits):
+        qc = qubits[i]
+        measure_qubit(qc, bob_bases[i])
+
+        # Execute the circuit
+        simulator = Aer.get_backend('qasm_simulator')
+        job = execute(qc, simulator, shots=1)
+        result = job.result()
+        counts = result.get_counts(qc)
+
+        # Get the measurement result
+        bob_results.append(int(list(counts.keys())[0]))
+
+    # Step 3: Alice and Bob announce their bases
+    key_bits = []
+    for i in range(num_bits):
+        if alice_bases[i] == bob_bases[i]:
+            key_bits.append(alice_bits[i])  # Keep the bit if bases match
+
+    return alice_bits, bob_results, key_bits
+
+if __name__ == "__main__":
+    num_bits = 10  # Number of bits to transmit
+    alice_key, bob_key, shared_key = bb84_protocol(num_bits)
+
+    print("Alice's bits: ", alice_key)
+    print("Bob's measurements: ", bob_key)
+    print("Shared key: ", shared_key)