John Preskill (Professor of Theoretical Physics, Caltech) is a leader in quantum field theory and quantum information who established the Institute for Quantum Information and Matter at California Institute of Technology. His lectures on quantum computation - available online since 1997 - continue to profoundly influence the subject.
PI: Scientific discoveries often happen where two or more fields intersect. What is your favourite scientific intersection, and why?
JP: The intersection of quantum information and quantum gravity is a fertile area right now. We understand better now that different phases of matter have different kinds of quantum entanglement – that is, different correlations between different parts of the system. But now we're getting the idea that we can understand spacetime more deeply using ideas from quantum information and quantum computing – these same ideas about correlations and entanglement.
There have been hints for some time now that spacetime is not really a fundamental concept. If you try to probe the structure of spacetime at smaller and smaller distances, with better and better resolution, eventually you have to add so much energy that you make a black hole. Therefore, thinking of spacetime as having structure on a finer scale than that doesn’t make sense operationally. This suggests that there is some more fundamental idea from which spacetime emerges.
We're fixated on this concept that spacetime emerges from entanglement. So far we just have pieces of the puzzle – hints that that idea is on the right track. Finishing the hunt is part of the fun.
PI: "I am a physicist because..."
JP: ... I don’t mind being confused most of the time. Ninety nine percent of the time there is something I'd like to understand, but I don't. That's actually okay, because you realize that eventually you're going to figure it out, and that kind of keeps you going. Quite often I read a scientific paper and don't understand it at all, but then I put my mind to it, and I get there. I try to let my students see how confused I am. My hope is that it inspires rather than terrifies them.
PI: When historians look back at this moment in science, is there something you think they'll see as obvious, that we are just missing right now, or that this time will be noted for?
JP: We're in the early phases of exploring a new frontier; sometimes I like to call it the entanglement frontier. We've always thought of "quantum" as meaning the behaviour of very, very small things, but now we have these tools, which we just acquired very recently, which allow us to build larger, more complex quantum systems, and control them well. We can scale quantum systems up to a larger size, and let the weirdness of the quantum world become more microscopic.
A hundred years from now, that's going to be a huge part of what physics is about: understanding what kinds of new phenomena you get when you put together quantum systems in just the right ways, which are highly entangled and very non-classical, and therefore hard to simulate using ordinary digital computers. They will behave in ways we will find surprising and delightful.