Error in notebook for 'Training' video

In notebook for ‘Training’ course, I think there is a error with this code block:

# helper function: perturbs an image to a specified noise level
def perturb_input(x, t, noise):
    return ab_t.sqrt()[t, None, None, None] * x + (1 - ab_t[t, None, None, None]) * noise

there should be also .sqrt() to in second ab_t?