single-column revtex4-1 adds a page break after the title section

By default, revtex4-1 reserves a whole page to typeset the title and the author(s) information; to change this behaviour, you need to use the notitlepage class option:

\documentclass[notitlepage]{revtex4-1}

This has been fixed in revtex4-2. The Author's Guide says

The onecolumn option no longer defaults to creating a separate title page.

And indeed, changing to \documentclass{revtex4-2} in the MWE posted above results in a single-page document.