One of the reasons it’s so difficult to make a quantum computer, and one of the reasons I'm a little skeptical at the moment, is the reason the quantum world seems so strange to us is that we don’t behave quantum mechanically. You could run toward a wall from now until the end of the universe and bang your head in to it and you’d just get a tremendous headache.  But if you're an electron, there's a probability that if I throw it toward the wall that it will disappear and appear on the other side due to something called quantum tunneling.

Those weird quantum behaviors are manifest on small scales.  We don’t obey those behaviors because we’re large classical objects and the laws of quantum mechanics tell us, in some sense, that when you have many particles interacting at some level, those weird quantum mechanical correlations that produce all the strange phenomena wash away.  And so in order to have a quantum mechanical state where you can distinctly utilize and exploit those weird quantum properties, in some sense you have to isolate that system from all of its environment because, if it interacts with the environment, the quantum mechanical weirdness sort of washes away.

And that’s the problem with a quantum computer. You want to make this macroscopic object, you want to keep it behaving quantum mechanically which means isolating it very carefully from, within itself, all the interactions and the outside world.  And that’s the hard part -- isolating things enough to maintain this what's called quantum coherence.  And that’s the challenge and it’s a huge challenge.

In Their Own Words is recorded in Big Think's studio.