How can I evict an ex who has been living in jointly owned property that was supposed to be quitclaimed to me as the result of a decree?

You have two issues that need to be addressed.  If he has violated a court order and failed to execute and deliver a deed to you, then you need to bring a contempt action to enforce the divorce decree.  If you want to evict him, you need to serve a 30 day notice to quit on him, wait the 30 days, and then serve and file a summary process complaint.  This is a complicated area of law.  I recommend that you contact a lawyer to do the eviction.