rose.blog

Hi everybody,

Today I am going to provide some background information on the stuff we make our processors out of. As you’re probably aware, conventional processors, like Athlons and Pentiums, contain a lot of silicon. Maybe you have wondered why this is. Why silicon and not beryllium? Or lead?

There are many good reasons. One of them is that it is particularly easy to make a very important device, the transistor, using silicon. In fact even though Bell Labs invented the transistor, it was Texas Instruments who first commercialized it, mainly because they figured out how to switch from the Bell Labs style germanium version to a nice, simple and cheap silicon version.

The silicon based transistor worked so well that it, and its descendants, have been the workhorse of nearly every processor used from the very beginning of microprocessors through to today.

I say nearly because there is a different way to build processors (using metals) that has been lurking in the background for about 20 years, showing a lot of promise, but never taken up by any of the major processor companies as the basis for a product line (TRW’s efforts notwithstanding).

These metal-based processors are quite unusual. One thing about them is that in order for them to operate, they need to be cooled to nearly absolute zero using special refrigerators. At these very low temperatures the metals that form the processor’s circuits become what are called superconductors. Whenever anyone says “superconductor” just think “really cold metal”.

Why go to the trouble of doing something like this? Historically arguments for metal-based processors have been that (1) since they’re made out of superconductors, they generate much less heat than conventional processors (true); (2) for some technical reasons you can operate at clock speeds up to about 100 GHz without alot of problems (true); so if you want a really fast, really low power processor, here’s a way to do it.

History says though that these benefits by themselves just aren’t enough to even TRY to commercialize this type of metal-based processor, especially given the temperature constraints (which probably limits applicability to “capability class supercomputer” type stuff). Just too much risk for not enough reward.

BUT what if there was a way to use the “really low power & really fast” benefits to gain some other really valuable advantage?

What D-Wave has done is begun with the standard approaches to building metal-based processors and modified them in such a way that these processors use quantum mechanics in order to accelerate computation.

When you look at one of our processors with your naked eye, what you see is a fine mesh of metal circuitry (the metal is niobium) on a 5 square millimeter chip. This metal circuitry is the top metal layer in a multi-layer metal/insulator/metal/repeat many times/ sandwich. This top metal layer contains things like contact pads for connecting the chip to wires that carry information to and from the processor.

Here is a picture of one of our processors in a test system, to give an idea of what it looks like. The chip in the middle is 5 square mm in size.

Cool eh.

So why are we using these metal-based processors as the basis for our approach to building quantum computers? There’s one underlying fundamental reason: we know how to build really big things using superconducting metals that behave quantum mechanically.

Superconductors are the only type of material that we know of where big lithographically defined devices (like really big. Like centimeter on a side big.) can be built that behave just like they were atomic-sized. The reason for this behavior is highly technical – is has to do with the types of particles in the material. In a superconductor all of the “particles” that carry charge around can exist in the exact same state, so when you look at a whole lot of these particles (many trillions) it can be just like looking at only one (which is “very quantum mechanical”).

This property allows us to build circuits out of superconductors that, if we are really smart and really careful, can be made to act like “circuits of atoms”. We can use the fact that really big things (which we can easily build today using conventional fabrication techniques) can be made to behave like really small things to try to build real quantum computing architectures.