Hi, Richard, Philip M, etc.

I think this blog is a great idea, as a Yank I’m a bit jealous. We don’t, as of yet, have a project like this Ideas Factory. In the triennial review of our National Nanotechnology Initiative there is a call for funding along these lines for “experimental demonstrations that link to abstract models and guide long-term vision.” That quote refers to “Site-Specific Chemistry for Large-Scale Manufacturing.” Hopefully, when such a project begins here, we too will have a blog like this where laymen, like myself, can express their thoughts.

I have a few thoughts on the technical and societal aspects of this technology, but I will only write about one now.

It is quite obvious that one technology in particular, that of the scanning probe microscope, has inspired the idea of the software control and manipulation of matter for the purposes of manufacturing. It is one of those wonderful instances in science where a negative has been turned into a positive. The negative being, the fact that at the nanoscale, it is impossible to observe anything without interacting with it. Instead of lamenting this fact, researchers embraced this phenomenon to deliberately use these devices to pick-up an deposit individual atoms. But what of the original desire, to observe without interaction? It seems as though the laws of quantum mechanics allow a loop-hole.

The idea in question is that of counter-factual or interaction-free measurement, also known as quantum interrogation. It is best described by the classic bomb-detector thought experiment. The purpose of the set-up is to detect a bomb which is sensitive to a single photon without detonating it. You start out with a half-silvered plane mirror (Mach-Zehnder interferometer set-up), a photon both passes through and is reflected by the mirror according to the laws of quantum mechanics. In the part of the wave-function where the photon passes through the mirror it interacts with the bomb thus detonating it, but even if the photon does not take this path in reality, you can still gather information about the interacting path from the non-interacting path taken where the photon is reflected by the mirror. By doing this you can determine that the bomb in not a dud without detonating it. This only works half the time, because in the other half the photon destroys what you are trying to observe. However, using the quantum zeno effect it is possible to improve your chances arbitrary. So it is possible to gather information about something without interacting with it.

So the question is what might this mean for nanotechnology? It has been suggested that techniques like the above could be used to watch a live movie of a Bose-Einstein condensate without destroying it. No doubt, there are many other things that could be observed in this way. Specifically to the task of this Ideas Factory, could one use this in conjunction with SPMs to both manipulate and see at the same time? The use of scanning probe microscopes is a bit like a blind person “seeing” his world by touching everything. It is hard to imagine a blind man getting a job making fine watches with delicate clockwork. The simple act of checking his work would destroy it in many cases. The same could be said about the Drexlerian vision of extending the capabilities of SPMs to create a working nanofactory. It is the nanofactory, or something very much like it, that this Ideas Factory seems to be all about. Presently, it is hoped that detailed computer models will allow us to predict problems ahead of time and find solutions beforehand. A great example of this is the paper by Jingping Peng, Robert Freitas et al. where reconstruction issues involving carbon dimer placement prompted the development of a placement strategy that stagers reaction sites. Another example of this sort of thing is when a team discovered that the properties of a surface that they where studying mysteriously changed after being imaged by an SPM. It was discovered by simulation that what was happening was that material from the surface was being picked-up by the tip thus confusing their equipment. As wonderful as simulations are, wouldn’t it be beneficial if you could both work *and* see at the nanoscale like we do at the mesoscale?

I am interested to know to what extent participants in the Ideas Factory from the field of microscopy, Philip Moriarty and company, are aware of and employ quantum interrogation techniques. It is my understanding that this idea is only now beginning to be exploited. Paul Kwait of the University of Illinois has used the technique to get answers from a quantum computer without it “actually running”.

Here are some relevant links:

Conclusion to the triennial review of the U.S.’s National Nanotechnology Initiative:

A paper by Paul Kwait et al. that involves interaction-free measurement:

I believe there is also a paper in Nature that deals with his work in quantum computing. No doubt, Ideas Factory participants are all subscribers.

Paper on carbon dimer placement to synthesize diamond by Peng, Freitas, et al:


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