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Recent research at IBM has found a way to store 1 bit of data in 12 atoms.

While that is a big accomplishment compared to what we have today, it does seem like a waste to a non-physics eye like me.

From this figure on the same page:

enter image description here

it looks like we can determine 1 and 0 based on the alignment of magnetic properties of 12 atoms.

But why is a smaller unit, like just one atom not good enough?

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    $\begingroup$ 1 bit of information means that there are two stable states which may be distinguished, into which you may transfer the system, and it'll remain in that state. How are you going to achieve this with 1 atom? $\endgroup$
    – valdo
    Commented Feb 1, 2012 at 22:28
  • $\begingroup$ @valdo: easy - left to right magnetization is one state, opposite is another. $\endgroup$
    – Lazer
    Commented Feb 1, 2012 at 22:51

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I don't think that this is a physics restriction, but one of current engineering capability. As you link points out, using 12 atoms allowed the information to be retained without effecting the information stored next to it. You will also need enough data-mass to allow for the reading and writing of the information without affecting the data next to the one of interest. In theory the binary data could be stored in other characteristic so an individual atom, but we (IBM) currently don't have a way to do this.

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  • $\begingroup$ Just to add a little bit to your answer (and without a specific knowledge of this IBM development): The mass of atoms is probably related to the uncertainty principle, where measuring a physical property of just one atom would probably alter its state and instead, when measuring 12 with current equipment would probably be more stable and not become altered due to the measurement. $\endgroup$
    – Chiguireitor
    Commented Feb 2, 2012 at 15:21
  • $\begingroup$ @Chiguireitor But wouldn't ANY measurement ulter the state of the atoms as a whole? $\endgroup$
    – Revo
    Commented Feb 2, 2012 at 21:07
  • $\begingroup$ @Revo indeed, but as a stable "molecule" that 12-atom compound will probably restore itself to the original state after measurement, hence the need for that structure. It is somewhat like termoplastic materials that after being damaged can restore themselves by being applied heat. $\endgroup$
    – Chiguireitor
    Commented Feb 3, 2012 at 13:27
  • $\begingroup$ @Chiguireitor That is very weird. I never came across anything like this in the postulates of quantum mechanics. Are you saying that the state after "collapsing" to one of the eigen states of the measured observable have a memory so it will evolve back to its state after collapsing?! I do not think this is possible because once the state collapsed, it became a different state. $\endgroup$
    – Revo
    Commented Feb 3, 2012 at 13:56
  • $\begingroup$ @Revo I don't know exactly how IBM achieved this, but i know this happens in protein bonding where certain proteins bend according to what other proteins are they bonded due to some interactions between their bonding atoms... however, i'm no expert so don't take my word for it. EDIT: And i'm not talking about "memory" per se, more like a reciprocal state where you measure just one "border" atom of structure and the "stable" bond of the rest stabilizes the mesured part after disturbance. $\endgroup$
    – Chiguireitor
    Commented Feb 3, 2012 at 18:59
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For any kind of magnetic data storage you need a magnetic state that is stable over time. The magnetic moment of an isolated single atom does not have any preferred direction, therefore the energy states are degenerated.

The 12 atoms used in this experiment is not a lower limit, in principle it can also work with 2 atoms given the right magnetic interactions between these two atoms. As you lower the number of atoms the probability of a flip of the magnetic moment due to thermal fluctuations of the whole cluster increases dramatically, so your information would be lost after a short time.

One atom can only be used if you use a different property, like position to store data. IBM even developed such a system with an atomic force microscope that could in principle use only a single atom but I am not sure how far they are with a practical application (Millipede memory).

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  • $\begingroup$ Is the fundamental difference with "quantum computing" that they allow the degenerate energy states? So would it be correct to say that this devices pushes the limit of deterministic computing? $\endgroup$
    – Alan Rominger
    Commented Feb 1, 2012 at 20:03
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    $\begingroup$ This is definitely pushing the limits of deterministic data storage but I would not compare it with quantum computing, as this whole approach here is only storing and reading bits of data and there is no computation of any kind. $\endgroup$
    – Alexander
    Commented Feb 1, 2012 at 22:13
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1 atom can be used to store information, it's just not quite as convenient.

10 years ago IBM used an Atomic Force Microscope (AFM) to write the word "IBM" in individual Xenon (?) atoms on a silicon wafer.

Of course you needed an AFM and the sample had to be kept at a few Kelvin in presumably a rather impressive vacuum.

IBM written with individual atoms

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    $\begingroup$ "1 bit can be used to store information", well that can't be argued with. :) $\endgroup$
    – Alexander
    Commented Feb 1, 2012 at 22:18
  • $\begingroup$ What is in this picture? What are those mountain like peaks? $\endgroup$
    – Lazer
    Commented Feb 2, 2012 at 6:37
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    $\begingroup$ @Lazer they are the AFM 'image' of single atoms spelling out IBM $\endgroup$
    – Martin Beckett
    Commented Feb 2, 2012 at 6:47
  • $\begingroup$ AFM: en.wikipedia.org/wiki/Atomic_force_microscopy $\endgroup$
    – BlueRaja - Danny Pflughoeft
    Commented Feb 2, 2012 at 6:51

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