At present, the closest you can come is to redraw it at a larger size using the figsize function. It expects dimensions in inches, which caught me out the first time I tried to use it.
There are some plants for a rich backend that would allow plots to be manipulated live, using HTML5, but I think it will be a few more months before that's ready.
If you're using the notebook on your local computer, for now the easiest option might be not to use inline mode, so the plots pop up as separate windows.
mpld3 slowed down the execution of my notebooks. I found it better to use the nbagg backend that provides the same interactive tools but also allows to save graphs by the right-click menu:
import matplotlib
matplotlib.use('nbagg')
import matplotlib.pyplot as plt
matplotlib.use('nbagg') didnt work for me either. I did find mdplt3 quite slow. Instead of zooming, I ended up resizing my figure (making it big), using this post: Plot width settings in ipython notebook