Benefit of published papers for grad admissions I'm currently finishing up my 3rd year of undergrad at a large state school and wanted to know how helpful first-author papers are for someone in physics when applying to grad school at a place like MIT or Caltech.

I've had the chance to work with two great professors in different areas of quantum physics. Thus far, I've published three papers as first author (one in PRX, two in PRL) and have three other papers in the works (one accepted to nature physics assuming some revision). Since my work was quite substantial, the postdocs and graduate students in both groups are using my techniques to study other problems and I anticipate having at least 5 other papers with my name in the 2nd and 3rd author position by the time grad admissions comes around.

In all cases I found/solved problems that were far beyond what my supervisors thought an undergrad could solve and they are both very happy with my work. I am wondering how much this would help with grad admissions? The reason I'm asking this here is I almost feel silly asking my supervisors since the schools I mentioned seem extremely prestigious and I wanted to gauge if I had any chance.
Any paper you publish as an undergraduate is a huge benefit to your application. Most grad school applicants do not have any publications, let alone five with some first author ones. You're way ahead of the curve, and it should make a very substantial positive difference in your application.

Of course, this does not constitute a guarantee that you will actually be admitted to the very best places. Other factors go into the consideration as well, but having read several hundred applications, I can tell you that your publications will be seen very positively.