Reflections of a stormy petrel

SHIELD had the Tesseract before Loki did. And Loki had Solvig and Hawkeye, and no doubt had questioned them. As for Banner being there or not, Loki would simply have gone into the enemy quarters with the intention of using what he found, whatever it was. He could not, for that matter, know that Iron Man and Captain America would both be there and could be manipulated into strongly disliking each other, could he now? The one thing he could be certain of was that some time after his "capture", Barton would head a task force against the Heli-Carrier. One thing that is certain is that Loki was in touch with Barton or someone in his team, or else the team could not have found the Heli-Carrier, which was invisible. They came following the energy signature of Loki's sceptre, and they used the Tesseract to do so - remember that one moment before Barton begins his attack, Banner looks at the screen where the Tesseract has been found, and goes "Oh my God!" Evidently the screen has just told him that the Tesseract is right outside.