# Aligning only on one side, single line

I would like to get something like this:

But if I write something like

\label{key} \begin{aligned} \theta\left( c_1\ket{\alpha}+c_2\ket{\beta} \right)&=UK\left( c_1\ket{\alpha}+c_2\ket{\beta} \right)\\ &=c_1^\ast UK\ket{\alpha}+c_2^\ast UK\ket{\beta}\\ &=c_1^\ast\theta\ket{\alpha}+c_2^\ast\ket{\beta} \end{aligned}


outputs the aligned text on the right aligned so that the middle of the alignment coincides with the arrow and the left text. Like this:

How can I change that?

And excuse the wording, explaining my idea was quite difficult

• Welcome to TeX.SX! Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. – Heiko Oberdiek Mar 17 '18 at 19:42
• You certainly do not have this result with the code you posted. – Bernard Mar 17 '18 at 19:46

The question is very unclear but I think you want something like

\documentclass{article}
\usepackage{amsmath,braket}
\begin{document}

\label{key} \ket{\alpha} \stackrel{K}{\longrightarrow} \begin{aligned}[t] \theta\left( c_1\ket{\alpha}+c_2\ket{\beta} \right)&=UK\left( c_1\ket{\alpha}+c_2\ket{\beta} \right)\\ &=c_1^\ast UK\ket{\alpha}+c_2^\ast UK\ket{\beta}\\ &=c_1^\ast\theta\ket{\alpha}+c_2^\ast\ket{\beta} \end{aligned}
\end{document}


Too long for a comment.

The code snippet extended to a full MWE gives:

\documentclass{article}
\usepackage{amsmath}
\usepackage{braket}
\begin{document}
\label{key} \begin{aligned} \theta\left( c_1\ket{\alpha}+c_2\ket{\beta} \right) &=UK\left( c_1\ket{\alpha}+c_2\ket{\beta} \right)\\ &=c_1^\ast UK\ket{\alpha}+c_2^\ast UK\ket{\beta}\\ &=c_1^\ast\theta\ket{\alpha}+c_2^\ast\ket{\beta} \end{aligned}
\end{document}


The aligning is correct and there is no arrow, no summation signs, ...