That sounds a lot closer to Canadian employment law, not US law. In most states, at-will employment is indefinitely 2-way. Employers are usually not required to give you any notice/reason/benefit beyond what is in the employment contract you sign. Conversely, employees have the same freedom. I've been at my job over ten years now and I could quit today with 0 notice or penalty. I don't have to tell them why or where I'm going, just return my work equipment and collect a prorated final check. I could do a lot more damage to them than they could do to me and I like it that way.