Fibre based QKD Simulator

Question

I'm trying to simulate a quantum fibre channel, but I keep getting an error message saying the model qutip has no attribute depolarize. The library I imported are qutip as qt, lumpy as np and random. Here's my definition for the quantum channel: channel = qt.to_super(qt.depolarize(1 - drift_rate / fibre_length)). How do I go about this problem?

import qutip as qt
import numpy as np
import random

# Set up the simulation parameters
fibre_length = 10  # in km
drift_rate = 0.1  # in degrees/km
error_rate = 0.05  # in decimal fraction
num_iterations = 1000

# Create the initial quantum state
initial_state = qt.basis(2, 0)

# Define the channel
channel = qt.to_super(qt.depolarize(1 - drift_rate / fibre_length))

# Run the simulations
polarizations = []
for i in range(num_iterations):
    polarization = initial_state.expect(qt.sigmaz())

    # Apply the channel
    for j in range(fibre_length):
        unitary = qt.tensor(qt.qip.operations.rotation_gate(random.uniform(0, 2 * np.pi), 'x'), qt.qeye(2))
        channel = channel * qt.to_super(unitary)
        polarization += random.uniform(-1, 1)  # Add random polarization errors

    final_state = qt.vector_to_operator(channel * qt.operator_to_vector(initial_state))

    # Add random quantum errors
    if random.random() < error_rate:
        noise = qt.rand_unitary(2)
        final_state = noise * final_state

    polarization = qt.expect(qt.sigmaz(), final_state)
    polarizations.append(polarization)

# Compute the statistics
mean_polarization = np.mean(polarizations)
std_polarization = np.std(polarizations)
print(f"Mean polarization: {mean_polarization}")
print(f"Standard deviation of polarization: {std_polarization}")