How do I robustly typeset a double-hat?

Question

I'm trying to typeset a symbol with two hat accents (useful for denoting superoperators in quantum mechanics, for instance), but \hat{\hat{L}} produces too much space between the hats. I found one approach on a LaTeX forum that seems to work, but it requires manual adjustment for each letter that I might want to typeset. If anyone has any suggestions, I'd appreciate it. Thanks!

Answer 1

Well, I wrote that suggestion at LaTeX Community, but there I assumed the person wanted fine-grained control. If you don't, then maybe something like this would be more suitable? You may need to tweak the -0.35ex to your liking, though not separately for each character.

How about this?

\documentclass{article}
\usepackage{amsmath}
\usepackage{accents}
\newlength{\dhatheight}
\newcommand{\doublehat}[1]{%
    \settoheight{\dhatheight}{\ensuremath{\hat{#1}}}%
    \addtolength{\dhatheight}{-0.35ex}%
    \hat{\vphantom{\rule{1pt}{\dhatheight}}%
    \smash{\hat{#1}}}}
\begin{document}

$\doublehat{x} \doublehat{L} \doublehat{\prod}$
\end{document}