You can look at standard T-mouldings, uneven T-mouldings or "reducers". There are literally dozens of different profiles out there. You will need to know three numbers:
1) height of rubber mat
2) Height of carpet
3) height difference between the two (deduced by using first two numbers...but nothing in flooring is "perfect".

You can look at plastic, rubber, laminate (MDF) or even oak trim. Your flooring store will help you with attachments/how to get it to "stay". If this is onto a slab, you have limited options. If this is going over plywood you will have an easier time of it.