# BibLaTeX doesn't print bibliography

I'm using sharelatex to work on a project with a fellow student, but we are unable to get the biblatex to be printed. The file we use with for our bibliography is currently stored as sample.bib. Can anybody see what we are doing wrong?

\documentclass[%
aip,
jmp,%
amsmath,amssymb,
%preprint,%
reprint,%
%author-year,%
%author-numerical,%
]{revtex4-1}

\usepackage{biblatex}
\usepackage{graphicx}
\usepackage{dcolumn}
\usepackage{bm}
\usepackage{lipsum}

\begin{document}

\title{Review essay: Here comes our title, which is very loooooooooooooooong}

\vspace{150px}
\begin{abstract}
\textbf{\begin{center}name 1 (student number) name 2 (student numeber \\ University \& Vrije University\\ \today \end{center}}

\end{abstract}

\maketitle

\begin{quotation}
\lipsum[1]

\end{quotation}

\section{\label{sec:level1}Introduction}
\lipsum[1-5]

\section{references}
\printbibliography

\end{document}


## sample.bib

@article{einstein,
author =       "Albert Einstein",
title =        "{Zur Elektrodynamik bewegter K{\"o}rper}. ({German})
[{On} the electrodynamics of moving bodies]",
journal =      "Annalen der Physik",
volume =       "322",
number =       "10",
pages =        "891--921",
year =         "1905",
DOI =          "http://dx.doi.org/10.1002/andp.19053221004",
keywords =     "physics"
}

@book{dirac,
title={The Principles of Quantum Mechanics},
isbn={9780198520115},
series={International series of monographs on physics},
year={1981},
publisher={Clarendon Press},
keywords = {physics}
}

@online{knuthwebsite,
author    = "Donald Knuth",
title     = "Knuth: Computers and Typesetting",
url       = "http://www-cs-faculty.stanford.edu/~uno/abcde.html",
keywords  = "latex,knuth"
}

@inbook{knuth-fa,
author = "Donald E. Knuth",
title = "Fundamental Algorithms",

Add \nocite{*} before \printbibliography. By default, references which are not cited in the text do not appear in the bibliography.