About the one big problem that hinders us from physically implementing everything that we’ve learnt so far, namely decoherence, as well as how we can start to deal with it via some elementary error correction.
In principle we know how to build a quantum computer: we can start with simple quantum logic gates and try to integrate them together into quantum networks. However, if we keep on putting quantum gates together into networks we will quickly run into some serious practical problems. The more interacting qubits involved, the harder it is to prevent them from getting entangled with the environment. This unwelcome entanglement, also known as decoherence, destroys the interference, and thus the power, of quantum computing.