Jeffrey Shainline: Neuromorphic Computing and Optoelectronic Intelligence | Lex Fridman Podcast #225

The following is a conversation with Jeff Schoenlein, a scientist at NIST interested in optoelectronic intelligence. We have a deep technical dive into computing hardware that will make Jim Keller proud. I urge you to hop on to this roller coaster ride through neuromorphic computing and superconducting electronics, and hold on for dear life. Jeff is a great communicator of technical information, and so it was truly a pleasure to talk to him about some physics and engineering. To support this podcast, please check out our sponsors in the description. This is the Lex Fridman Podcast, and here is my conversation with Jeff Schoenlein. I got a chance to read a fascinating paper you, um, authored called Optoelectronic Intelligence. So maybe we can start by, uh, talking about this paper, and start with the basic questions. What is optoelectronic intelligence?

Yeah, so in that paper the, the concept I was trying to describe is sort of an architecture for building brain-inspired computing that leverages light for communication in conjunction with electronic circuits for computation. In that particular paper, a lot of the work we're doing right now in our project at NIST is focused on superconducting electronics for computation. I'll go into why that is, but, uh, that might make a little more sense in context if we first describe what that is in contrast to, which is semiconducting electronics.

Mm-hmm.

So is it worth taking a couple minutes to describe semiconducting electronics?

It might even be worthwhile to step back and, uh, talk about electricity and circuits and how circuits work-

Right.

... uh, before we talk about superconductivity.

Right. Okay.

How does a computer work, Jeff?

Well, I, I won't go into everything-

(laughs)

... that makes a computer work, but let's talk about the basic building blocks, a transistor, so... And even more basic than that, uh, a semiconductor material, silicon, say. So, uh, in, in silicon, silicon is a semiconductor, and what that means is at low temperature there are no free charges, no free electrons that can move around. So when you talk about electricity, you're talking about predominantly electrons moving to establish electrical currents, and they move under the influence of voltages. So you apply voltages, electrons move around. Those can be measured as currents, and you can represent information in that way. So semiconductors are special in the sense that they are really malleable. So if you have a, a semiconductor material, it, you can change the number of free electrons that can move around by putting different elements, different atoms in lattice sites. So what is a lattice site? Well, a semiconductor is a crystal which means all the atoms that comprise the material are at exact locations that are perfectly periodic in space. So if you start at any one atom and you go along the what are called the lattice vectors, you get to another atom and another atom and another atom, and for high-quality devices it's important that that is a, a perfect crystal with very few defects. But you can intent- intentionally replace a silicon atom with, say, a phosphorus atom, and then you can, you can change the number of free electrons that are in a region of space that has that excess of what are called dopants. So picture a device that has a left terminal and a right terminal, and if you apply a voltage between those two, you can cause electrical current to flow between them. Now we, uh, add a third terminal up on top there, and depending on the voltage between the left and right terminal and that third voltage, you can, you can change that current. So what's commonly done in digital electronic circuits is to leave a fixed voltage from left to right and then change that voltage that's applied at what's called the gate, the gate of the transistor. So, um, what you do is you, you make it to where there's an excess of electrons on the left, excess of electrons on the right, and very few electrons in the middle, and you do this by changing the concentration of different dopants in the lattice spatially. And then when you apply a voltage to that gate, you can either cause current to flow or turn it off, and so that's sort of your zero and one. You, if you apply voltage, current can flow. That current is representing a digital one, and, uh, from that, from that basic element, you can build up all the complexity of digital electronic circuits that have really had a profound influence on our society.