1024 bits stored in a single molecule?

From: Hal Finney (hal@finney.org)
Date: Sun Dec 01 2002 - 15:17:43 MST


New Scientist reports on a new technique for storing and retrieving
data using quantum mechanics. The article is here,
http://www.newscientist.com/news/news.jsp?id=ns99993129, with the
abstract available from
http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JCPSA6000117000015006903000001&idtype=cvips&gifs=yesXM
If you have access to a university computer you may be able to download
the whole article from that second link.

The researchers used nuclear magnetic resonance (NMR) technology to store
a 32 by 32 bit picture into liquid crystal molecules of 19 atoms each.
This is a total of 1024 bits, which they claim was stored in the 19
nuclear spins of a single molecule. They were then able to retrieve the
image and display the picture. This method is very similar to some of
the current early approaches to quantum computing.

However my understanding of quantum theory says that it is not possible
to store 1024 bits into 19 nuclear spins. Whether they realize it
or not, the researchers are working with a large number of molecules
simultaneously, and this is what makes it possible to put in and read
back that much data.

You could draw an analogy with a polarized photon, where you can in
principle put one photon into any of an infinite number of polarization
states. But when you read it back, you get only 1 bit of data. Now, if
you have zillions of photons in a laser beam, and you put them all into
the same polarization state, then you can indeed recover that state with
considerable precision, thereby retrieving a large amount of information.
Each photon is in exactly the same state, as in the NMR experiment, but
you need to use lots of them in order to recover the full information
about that state. Something similar is happening with the New Scientist
article, I am sure.

So overall I think this is a promising technique that could have practical
applications for information storage, but I don't agree with the "spin"
(pardon the expression) that is being put on the result.

Hal



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