Say, I have the following mapping:
map <F4> :execute "vimgrep /" .expand("<cword>") . "/j **" <Bar> cw<CR>
which (recursively) greps the current directory for instances of the word under the cursor and opens these files in the quickfix list window.
From the quickfix window, how do I launch the file that I open into a new tab? Enter just changes my current buffer in the window to that new file.