bob.py

import numpy as np
from braket.devices import LocalSimulator

from utils.bb84 import initialize_protocol, encode_qubits, measure_qubits, filter_qubits

NUMBER_OF_QUBITS = 12

# Load Alice data
alice_states = np.load("channel/alice_states.npy")
encoding_basis = np.load("channel/encoding_basis.npy")

# Bob chooses random measurement bases
_, _, measurement_basis = initialize_protocol(NUMBER_OF_QUBITS)

# Bob reconstructs Alice's circuit
circuit = encode_qubits(NUMBER_OF_QUBITS, alice_states, encoding_basis)

# Bob applies his basis
circuit = measure_qubits(circuit, measurement_basis)

# IMPORTANT: measure all qubits
circuit.measure(list(range(NUMBER_OF_QUBITS)))

# Run simulation
device = LocalSimulator("default")
result = device.run(circuit, shots=1).result()

measured_bits = np.array(result.measurements[0]).astype(int)

# Basis reconciliation (sifting)
alice_sifted = filter_qubits(alice_states, encoding_basis, measurement_basis)
bob_sifted = filter_qubits(measured_bits, encoding_basis, measurement_basis)

print("Bob measurement basis:", measurement_basis.astype(int))
print("Alice sifted key:    ", alice_sifted)
print("Bob sifted key:      ", bob_sifted)
print("Matches:             ", int(np.sum(alice_sifted == bob_sifted)), "/", len(alice_sifted))