Quantum computing will not rescue Moore’s Law

I found this video on quantum computing educational.  It confirmed some things that I’ve been pondering about quantum computing for a while, notably its limitations, which are discussed after about the five minute mark.

The strength of quantum computing is that it makes use of superpositions, the fact that quantum particles can be in multiple states at the same time.  But it’s always bothered me that superpositions disappear as soon as we try to determine what they contain (or, if you’re an adherent of the many-world interpretation of quantum mechanics, they spread to us in such a way that “we” only have access to one of the superposition branches).

It was fellow blogger Disagreeable Me who explained to me, and this video confirmed, that the way to think of quantum computing is as of a type of double slit experiment, but in the shape of a logic circuit.  Quantum computing allows for much more complex logic circuits than classical computing.  But as soon as that circuit outputs its results, decoherence, the wave function collapse, the disappearance or spread of the superposition, or whatever we call it, happens, and all the data aside from that in the collapsed state, disappears.

This means that quantum computing is good for certain types of CPU bound processes, such as calculations, but not for I/O bound processes, which is most of computing.  It means that those who believe that Moore’s Law is some cosmic law of physics are going to be disappointed when classical computing eventually hits fundamental physical laws.  Science fiction authors and singularity enthusiasts shouldn’t expect quantum computing to ride in and provide infinite computing power.

Of course, no one knows when Moore’s Law is going to end.  Experts seem to place it somewhere between 5 and 30 years.  I suspect we’ll only know about the end in retrospect years after we’ve hit it.  It won’t mean the end of progress in computing power, but it will mean that future gains past that point will be much harder, requiring alternate architectures.

Cosmic rays becoming an increasing problem for microchips. Threat to Moore’s Law?

When I first saw the title of this article, I thought it might be an alarmist piece of some kind about passenger safety from higher radiation doses while in the air, but it’s actually about a broader and more serious problem: The $8.5M Race to Protect Planes From Cosmic Rays.

It’s an invisible, but looming threat from outer space: distant cosmic events that can cause a computer, or even an aircraft, to crash here on Earth. Concerns have reached the point where a major European effort has been launched to investigate the devastation that can result from cosmic rays, wiping a device’s memory or damaging safety-critical aircraft electronics.

Some fear that Moore’s Law will soon break down — not because of a limit in our ability to make ever-smaller transistors at the scale of tens of nanometers (billionths of a meter) or less, but because of the neutron threat. As transistors shrink, errors can be caused by much smaller bursts of charge arising from neutrons. With higher densities, higher speeds and lower power consumption, microchip manufacturers are seeing neutron-induced soft errors occur more frequently.

Reading this story, I was reminded about the efforts underway to build a quantum computer, and how much energy is having to go into insuring that the components are isolated from the environment.  With varying degrees, it looks like this isolation problem will become increasingly an issue with classic processors.  And there’s no guarantee that the mechanisms of isolation will experience the same cost savings that computer chip technology has enjoyed.

Moore’s Law might not end because of some quantum tunneling limit.  It might end with the economics of protecting ever smaller logic components from the environment becoming increasingly untenable.  Toward its end, we might see a return to large expensive centralized supercomputers, in heavily shielded installations, that most of us access through the cloud for specific purposes.