The nature of quantum computation

Why is it so difficult to build a quantum computer? Quantum theory tells us that nature allows large scale quantum systems to be built and quantum coherently controlled. However we have not found such systems in nature nor built one despite a huge world wide effort over the last decade. In the last few years we have seen the development of small scale quantum information systems emerging. Though such small-scale quantum information systems can in principle run complex quantum computational tasks, the precision of our physical control directly bounds the complexity of possible calculations on these quantum systems. In this talk, we will detail the steps and gaps waiting for us to scale these systems up to large scale fault-tolerant quantum computation.