DW: Why should we care about quantum mechanics?

F. Duncan Haldane: Well it's the way the world works. Your iPhone only works because of quantum mechanical principles. One of the most amazing things that people found out in the 1930s was that in a semiconductor, what's actually conducting the electricity is not an electron but an empty space in the electron. And that's something you can only understand from quantum mechanics. So to even understand semiconductors and make a transistor, you need to understand quantum mechanics. You can't understand matter without understanding quantum mechanics.

Our understanding of the world is the resource from which all technology has sprung. The more you understand things, the more you can manipulate matter and do things you didn't know you could do. The more you understand something, the more someone can work with it. So we find the understanding and then hand it over to the technologists and they work out all kinds of amazing technology.

Reality seems more and more different the more we understand quantum mechanics.

Yeah, well the way of understanding quantum mechanics and the way we look at it has changed a lot during my career. In fact I hope I've played a little role in actually pushing this different way of looking at the quantum mechanics of condensed matter. There's this concept of entanglement - I think [Erwin] Schrödinger invented the term but [Albert] Einstein pointed out- that is such a strange consequence of quantum mechanics. In Einstein's view quantum mechanics had to be wrong, because it didn't work well with his gravity theory. So he proposed these experiments that didn't get done until long after he was dead to show that quantum mechanics could be thrown into the dustbin of history. And of course these experiments came out and showed exactly the crazy thing that Einstein thought was completely wrong.

But now we understand this weird entanglement thing properly. What Einstein thought was so crazy is now probably the essential property of quantum mechanics and all these new topological states which I and others have found. The underlying difference between them and the normal matter is the way they exist within this entanglement property. 

So now we're thinking entanglement has become one of the dominant themes in trying to understand this kind of matter. And this word wasn't really around for people working in condensed matter until maybe 10 years ago.  People are now saying that entanglement is the fuel that would power a future quantum computer. And it's the resource that would be expended in doing these computations. So suddenly these very obscure ideas have become mainstream and it has changed how we look at the whole thing. So I don't know when we'll get a quantum computer of the kind that is being envisioned now but I can certainly see that the advancements are happening so fast now that the improvement in these little quantum mechanical devices that people are making is much better than expected every year.

So the quantum computer would be a real step forward? Could we get them soon?

I don't know when they'll happen. But some kind of quantum information technology, or quantum processing of information, is going to come out of this. Just by understanding what happens, we're understanding questions that we couldn't answer before. We have all sorts of systems now where we can actually change the quantum state in a very controllable way.

What would be the advantage?

I don't know yet. It's up to the technologists to do something with it. But once you understand and then learn how to control nature, that's the resource that leads to technology. It's not our job to do the technology. We're just going to hand over the knowledge to the others. But it's amazing how new things are coming out all the time.

Frederick Duncan Michael Haldane is professor of physics at Princeton University and won the Nobel Prize in Physics in 2016 alongside David J. Thouless and John Michael Kosterlitz.