I have been recently introduced to QM and I am deeply interested in it. I have come to know that quantum cryptography, quantum computing, and quantum optics are the hot areas where research is going on. But I'm curious, is there theoretical research going on for understanding of the quantum world? Or is the quantum theory just like a tool to explore other things, like condensed matter? Do people do a PhD in 'quantum mechanics' the same way as 'high energy physics'? Or is QM too broad a topic.Forgive me if this is a naive question.