Return the phase damping Kraus operators

def depolarizing_operators(p):
    """
    Return the phase damping Kraus operators
    """
    k0 = np.sqrt(1.0 - p) * I
    k1 = np.sqrt(p / 3.0) * X
    k2 = np.sqrt(p / 3.0) * Y
    k3 = np.sqrt(p / 3.0) * Z
    return k0, k1, k2, k3