I am using the braket package to generate bra and ket vectors. However, I could not figure out how to do <0|0> using the package. Is there a command for this?
[Tex/LaTex] Braket notation in LaTeX
braketmath-mode
Related Solutions
The macros with uppercase initial are "self-expanding" based on the contents, as the documentation says. Just like it's not good to always use \left and \right, it's also good to choose with care between \Bra and \bra.
As far as the additional spacing is concerned, a solution is to load mleftright:
\documentclass{article}
\usepackage{amsmath}
\usepackage{braket,mleftright}
\mleftright
\begin{document}
\begin{align*}
\Bra{\frac{1}{\sqrt{2}}\left(\uparrow + \downarrow\right)}
&=\frac{1}{\sqrt{2}}\left(\Bra{\uparrow}+\Bra{\downarrow}\right)\\
\bra{\frac{1}{\sqrt{2}}\left(\uparrow + \downarrow\right)}
&=\frac{1}{\sqrt{2}}\left(\bra{\uparrow}+\bra{\downarrow}\right)\\
&=2 222 22\\
&=2\mathinner{222}22\\
\end{align*}
\end{document}
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}
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}
Best Answer
Use
\braket{0|0}: