4

I'm using the braket-package for using the braket notation. It works fine, but I've got some problems by using the package for writing a tensor product.

There is always a big gap between the ket and the bra by writing \ket{x}\bra{x}. So I want to have it like |x><x| and not like |x> <x|. Does anyone know this problem and perhaps also a solution for it?

Example:

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{braket}
\begin{document}
\begin{align*}
\ket{x}\bra{x}
\end{align*}
\end{document}
  • 1
    your question would be easier to answer if you made a small complete document showing your input and the bad space then people can test answers. (you can use the {} button in the editor to mark a mult-line code block) – David Carlisle Jan 21 '16 at 12:09
1

It's “by design”. The definitions of \bra and \ket are

% braket.sty, line 31:
\def\bra#1{\mathinner{\langle{#1}|}}

% braket.sty, line 32:
\def\ket#1{\mathinner{|{#1}\rangle}}

and \mathinner adds a thin space on either side of the construction.

If you want to remove those additional thin spaces (which is not a bad idea, by the way), you can redefine them like

\renewcommand\bra[1]{{\langle{#1}|}}
\renewcommand\ket[1]{{|{#1}\rangle}}

However, the sidebearings of \langle and \rangle will still leave a hole.

\documentclass[10pt,a4paper]{article}

\usepackage{braket}

\renewcommand\bra[1]{{\langle{#1}|}}
\renewcommand\ket[1]{{|{#1}\rangle}}

\begin{document}

\[
\ket{x}\bra{x}
\]

\[
\ket{x}\!\bra{x}
\]

\end{document}

enter image description here

You might check whether a \bra immediately follows a \ket:

\documentclass[10pt,a4paper]{article}

\usepackage{braket}

\renewcommand\bra[1]{{\langle{#1}|}}
\makeatletter
\renewcommand\ket[1]{%
  \@ifnextchar\bra{\k@t{#1}\!}{\k@t{#1}}%
}
\newcommand\k@t[1]{{|{#1}\rangle}}
\makeatother

\begin{document}

\[
\ket{x}\bra{x}
\]

\end{document}

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.