Lecture 2: “The Development of Quantum Error Correction”
When quantum computers were first discovered, it wasn’t clear that they could ever become practical, because it looked like it was impossible to correct errors on them. This was due to a theorems of quantum theory: the Heisenberg Uncertain Principle, which says that any measurement of a quantum system unavoidably changes the quantum state of the system. Thus, to figure out what the error is (so that you can correct it), you need to measure the system, which will inevitably disrupt the computation. This reasoning actually doesn’t hold, and it is possible to design quantum error correcting codes that can be used to make quantum computers fault-tolerant. We will survey the early developments of these fault-tolerant techniques.