[Tex/LaTex] Consistent vertical positioning of superscripts

Question

This is somehow a follow-up question to this one.

I've got the following math expression:
\nabla_y u_0^{(i)}\nabla_y v^{(i)}

However, no matte, whether I enclose the v in curly brackets or not (as indirectly suggested in the linked question), the last superscript ((i)) is always on a lower vertical position than the first superscript ((i)).

What is the optimal and advised method for ensuring that the superscripts are always on the same vertical position throughout my whole document?

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Edit
Thank's to karlkoeller's anwser, I ended up using two custom commands:

\newcommand{\supp}[1]{_{\vphantom{0}}^{#1}}
\newcommand{\subp}[2]{_{\vphantom{0}#1}^{#2}} 

The first is used when no sub-script should be printed and the latter is used for all combinations of super- and subscripts. E.g.

u\subp{\varepsilon}{(i)} \nabla v\supp{(i)}

Answer 1

This is because the first term has a subscript and the latter not.

One solution is to put a "phantom" subscript in the second term:

\(\nabla_y u_0^{(i)}\nabla_y v_{\phantom{0}}^{(i)}\)