Like many of the others, I would advise you to tell your wife, but not necessarily others, at least until it seems more convenient to do so. But it is important that you make it clear to her that you are expressing your own position, and not attempting to convince her of it. As long as that is clear, I think there is no significant danger of losing her. Consider the one friend who already knows; if they did not abandon you over your beliefs, why would your wife do so? On the other hand coming out and openly trying to convert her to atheism is almost certainly a bad idea, and would definitely result in a significant risk of losing her.

Also, I think this situation is quite common in social groups which are strongly religious, and that while you may overestimate the harm that would be done by simply being open with everyone, many of the comments here dramatically underestimate that harm, because most of the commenters were never in such situations in the first place. And I think it is very, very wrong and harmful to suggest "well, if they would react badly, then ** them all, abandon everyone you know and join a new community."