Applying for a PhD group who has asked for my research interests So I am applying to a research group in Quantum Optics  and Quantum 
Information. The professor has asked for my research interests and why I would like to join his group. My research interests are in the same field that he is researching but is not exactly to the point. For example, someone might be researching on the shape and size of the apple but I'm interested in the color and taste. We are still researching in the same field and I am also interested in doing my phd in the project he's working on. 

How do I express my research interests in this situation? Also, when someone asks "why are you interested in joining my research group", what are the usual points or aspects you talk about?
When someone asks, why are you interested in joining my research group, what are the usual points or aspects you talk about?


You have to read up on what the PI and the postdoc(s) and the students are doing and read some publications.  Then when you are asked that question, you can say what you found interesting or exciting about what is being done in that group.