The answer from @Mara provides all the tools you need, but there are still some caveats. Note that the first option will not set the spacing and the second option will cause a mismatch between the values and the labels.
I think the best solution would be to do all of these things:
- Set the yticks to 0:50
- Set the yticklabels to (0:50).^2
- Take the sqrt of your data before plotting it
