I'm a physicist with a CS degree and just started my PhD at a tech company (wanted to do applied research). It deals with large scale finite element simulations.

After reviewing their current approach, I think that a radically different method has to be applied (they are using a commercial tool which is very limited).

I'd rather base my research on an open source finite element solver and write a program which makes use of it. I'd like to develop this idea in the evenings, because that's the time that best suits me for programming (during the day I prefer reading and maths) and use it at a late stage of my PhD.

I'd like to have the option to release my program as open source on my website as a reference, for future personal or even commercial (e.g. consulting) use.

How can I make sure that my company doesn't claim the code ownership? I don't really

I thought that a version control system could help (check out only in the evening). This would document that I programmed not during regular office hours (documented elsewhere). But these data can be easily manufactured. Any other ideas?

I want to stress that I'm not interested in selling software. Jurisdiction is EU, if that matters. Thank you.