Can your job let you go if they find out you went on a job interview for another company?

I do not believe so no. They can't just fire you because of looking for another job.

I would keep it quiet, some companies are funny , perhaps take it as a sign of disloyalty and fabricate a scheme to retaliate. They would be concerned your happiness in work might influence job performance . Stuff like that (looking for a new job) spreads pretty fast in the workplace, especially amongst so-called friends.

Does your state have "At Will" employment laws? If it does, they COULD let you go. However, in most cases, the employers won't do that, because they're glad you're showing initiative, trying to better yourself, even if it means you're working for somebody else.

Depends on your state laws. Some allow business to fire without cause and some dont.

If your employment is considered at-will, that means your employer can let you go at any time for any reason. (It also means that you can quit at any time for any reason.) However, if it's for no cause, you can file for unemployment. Most companies don't fire someone for looking for another job; sometimes, you can use it as a bargaining chip in your favor to get a raise or extra benefits. You don't have to tell them about the interview; if you don't say and the company you're interviewing with doesn't spill the beans, how are they going to find out? If they do, say what you just said here about 3 years with no hope of moving up. Add a little sugar coating about how much you love working there, but your financial situation requires a change.