I applied online. The process took 2+ months. I interviewed at Georgia Tech (Atlanta, GA) in Mar 2012
Interview
Since this was a graduate student position, you just apply online. After acceptance there is a recruitment event in which new potential graduate students get the opportunity to meet with senior grads/postdocs and advisors. Individual meetings are set up for advisors you are interested in. Generally you will meet with the advisor, and separately with their students. Expect to hear back pretty quickly (~1 week).
Interview questions [1]
Question 1
What is your background in? Have you done undergraduate research? Which instruments are you familiar with?
I applied through college or university. The process took 2 months. I interviewed at Georgia Tech in Jan 2011
Interview
There is nothing like an interview process, just apply for a PhD. The most important step is the qualifiers exam - both oral and written. Unless one aces the qualifiers exam, one is not formally admitted to a PhD program.