I am pretty sure that Amherst College does not admit by major. Your chances of acceptance will not depend upon your major. However having an application with essays that sound sincere and genuine might help your chances.
I am more familiar with MIT but I am pretty sure that the two schools are similar in this respect. At MIT they use whatever you say is your intended major to match you with a freshman year academic advisor. That is all that they use it for. Then at the end of your freshman year you pick any major that you want (limited to majors that the school offers). I am pretty sure that Amherst College is the same in this regard.
Whether quantum computing will turn out to be lucrative or non-existent by the time that you get far enough to have a career in it is something that I would not be able to predict. However, there are careers in physics, and a lot of the coursework would be the same for perhaps the first two years of university, if not all four years of undergraduate study. For any physics major it would be a good idea to take quite a bit of physics, math, and some computer science. This is assuming that a school allows non-CS majors to take CS courses (which was allowed where I went to university, but might be restricted at some schools).
One last note is that your ECs do not need to match your intended major. For example on your list of ECs I see a research paper that uses some AI and computation algorithms and chess. These are good ECs for a wide range of potential majors, particularly for anything in the “TEM” part of “STEM”.