how can I create q bar symbol in math mode just like hbar?

Question

I need create a new math symbol a q with a bar just like command hbar (h with a bar)
Thanks for your help, this is an example
documentclass[]{article}
usepackage{polyglossia}
setmainlanguage{spanish}
usepackage[dvipsnames,svgnames,x11names,]{xcolor}

usepackage{graphicx}
usepackage{amsmath,mathtools,calculator}
usepackage{commath}
usepackage{xfrac}
usepackage{fancybox}
usepackage{multicol}
usepackage{nicefrac}% UNIDADES SI
usepackage{units}% UNIDADES SI
usepackage{pgf,tikz,tikz-3dplot}
usepackage{pgfplots}
usepackage[american]{circuitikz}

usetikzlibrary{arrows,patterns}
usetikzlibrary{decorations.text,bending}
usepgfplotslibrary{fillbetween}
usepgfplotslibrary{groupplots,polar} %
usepgflibrary{arrows.meta}
usetikzlibrary{arrows.meta}
usetikzlibrary{decorations.markings}
usetikzlibrary{decorations.text}
usepgfplotslibrary{fillbetween}
usepgfplotslibrary{groupplots,polar}

usepackage{cancel}
usepackage{wasysym}
usepackage{txfonts}
usepackage{smartdiagram}
usepackage{siunitx}

usepackage{fourier} % math font

usepackage{fontspec}
%defaultfontfeatures{Mapping=tex-text}
setmainfont{Arial}

begin{document}

This is the document

$left(x+aright)^2$, I need a $q$ command with bar

end{document}

egreg · Accepted Answer

It depends on the math font you're using.
With Computer Modern, taking the cue from https://tex.stackexchange.com/a/551356/4427, but also from the fact that the bar is at a different position, namely mathchar '26, we can do
documentclass{article}
usepackage{amsmath}

makeatletter

newcommand{addbar@}[2]{%
  makebox[0pt][l]{%
    raisebox{#1}[0pt][0pt]{%
      kern#2
      $m@thmathchar'26$%
    }%
  }%
}

DeclareRobustCommand{qbar}{text{addbar@{-1.5ex}{0.01em}}q}

makeatother

begin{document}

Normal size $qne qbar$ and subscript $X_{q}ne X_{qbar}$

end{document}

For the fourier math fonts, the code should be modified, because they don't have the required bar in the expected place. I'll solve this by horizontally scaling a minus sign.
documentclass{article}
usepackage{amsmath}
usepackage{fourier}
usepackage{graphicx}

makeatletter

newcommand{addbar@}[3]{%
  makebox[0pt][l]{%
    raisebox{#1}[0pt][0pt]{%
      kern#2
      scalebox{0.6}[1]{$m@th-$}%
    }%
  }%
}

DeclareRobustCommand{qbar}{text{addbar@{-0.8ex}{0.2em}{1}}q}

makeatother

begin{document}

Normal size $qne qbar$ and subscript $X_{q}ne X_{qbar}$

end{document}

how can I create q bar symbol in math mode just like hbar?

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