Will a paper published in an unrelated/other sub-discipline matter for graduate admission? My question is similar in spirit, though different in context (I think) to the question posted here.

My professor and I recently submitted a paper on arXiv (submitting for publication soon) that falls in the domain of quantum physics. Here's the link. I really liked enjoying working on the project, and I found it to be a valuable learning experience. 

I, however, don't wish to apply to graduate school in physics and specialize in quantum mechanics -- and the study of open quantum systems etc. Ideally, I'd like to join a mathematical physics research group, working of such topics as quantum gravity etc. with a mathematical focus or working on the mathematical aspects of various sub disciplines (quantum mechanics, topological insulators etc.).

I'm aware that being able to demonstrated the ability to do research prior to the graduate level is highly valued at US universities. My question is how will the graduate admissions committee(s) view this (potential) paper? It's already hard to get a spot in various mathematical physics research programs. Will they consider this publication as having no value to them, since the paper doesn't directly coincide with their sub-discipline? Or (if I spin it right), is it possible/expected that they'll view this as an indication of the student's ability to work outside of classroom, work on a project etc.

Edit -- How I intend to spin it. I'd like to use this paper to convince the graduate admissions committee follows: I come from a non-physics background ( major), and I have been studying physics/mathematics (in class, out of class etc.) for the last 2-3 years, and I wish to apply in 1-2 years. I started working on this paper after 1 year of studying physics in class. My first year was quantum mechanics (QM) heavy (three courses). The professor suggested the problem, which mostly used ideas from QM and some basic ideas from quantum information. I worked on the project with him and given my experience of having made the transition, making the first year of transition QM intensive and then working on a QM related problem and producing something with/with the help of a professor (regardless of its impact), I'm thinking of selling it as an indication that I can work outside of class, even when I (had to) make the transition; more importantly, given a problem related to the material I had covered after making the transition, I could produce something.

I know I'm more of "selling it" rather than "linking it with my future research interests." How does this sound in terms of having an impact on the committee and how they'll evaluate me (and my unusual situation).
Evidence that you can complete a research paper is a definite positive.  Many good students are not cut out for original research, so this should help make you an attractive candidate.  As you suggest, it is up to you to explain how the existing work does or does not relate to your intended research program as a graduate student.

NB: I am in the social sciences.