\begin{figure}[t]
\centering
\captionsetup{justification=justified,singlelinecheck=off}
\begin{tikzpicture}
\matrix (fig)[matrix of nodes]{
\includegraphics[width=2in]{example.pdf}
\end{tikzpicture}
\caption{}
\end{figure}
I'm using a revtex4-1 document class. I try to use justification=justified to justify the layout of the caption, but it still shows centering.
captionpackage is incompatible with therevtex4-1document class. Moreover, you're presumably using this document class because you've been asked to do so (e.g., to prepare your document for submission to a journal). It's almost certainly not a good idea to modify the formatting-related setting of such a specialized document class. – Mico Jun 25 '18 at 07:54