Scientists Find Flaw in Quantum Dot Construction

ThePolkapunk writes "Scientists have been having problems in predicting the behavior of Quantum Dots, which are considered to be the most likely material to be used to build nanocomputers. Physorg is reporting that physicists at Ohio University believe they've found the problem, and it's with a flaw in the construction of quantum dots. If their theory pans out, "It's one more step towards the holy grail of finding a better quantum bit, which hopefully will lead to a quantum computer."" We first mentioned this about six years ago.

Comments

I guess this seems as good a place as anywhere

[mcc]

to ask this...

The guy who wrote "the wellstone" is convinced that quantum dots can also be used to create programmable matter, something he came up with in one of his science fiction books.

I am just curious. Is this (programmable matter via quantum wells/dots) something that actual work is being done on anywhere, or that actual signs of progress can be seen in, or that Mr. McCarthy has the actual capacity to encourage actual science work to be done on? Or is this just a lone science fiction author running around trying to convince people to take him seriously?

Re:I guess this seems as good a place as anywhere

[wass]

Is this (programmable matter via quantum wells/dots) something that actual work is being done on anywhere, or that actual signs of progress can be seen in, or that Mr. McCarthy has the actual capacity to encourage actual science work to be done on?

First a note - All of my experience with quantum dots is at cryogenic temperatures, eg 4.2K and below, so I'm not aware of the behavior of systems at higher temperatures.

It sounds like this author is making very generalized hand-waving explanations about these fairly complex systems. And is vague enough so that if any effect is discovered, he'll claim that he "discovered" it first. But if he did claim that, it would be somewhat disingenuous because it's very difficult to predict what kind of coherent long-range many-body "emergent" patterns would manifest themselves. Ie, the low-level physics is hard, the fabrication is hard, determining large-scale effects is hard, etc. Heck, even describing a simple helium-atom is hard enough (the quantum-mechanical 3-body problem), with three interacting coulomb forces to work with in addition to the nuclear potential. So it sounds like he's handwaving, but in an attempt to claim prediction of any future discovery based on quantum-dots.

On a side note, though, all matter is already programmable by default. Phase transitions, for example, will happen at specific temperatures, or magnetic fields, etc, such that the macroscopic behavior of the material can be 'programmed' by pushing through the phase transition.

Re:I guess this seems as good a place as anywhere

[lgw]

Actual real-world viruses are genuine nanotechnology. Further, they have been evolving for thousands of years to kill humans. It's believed that actual real-world viruses killed 95% of humans in North America and 90% of humans in Central America soon after the Spanish began exploring. Actual real-world viruses are the best possible human-killing nanotechnology given actual real-world material and energy limitations, the laws of physics, and the fact we don't live in a science-fiction novel.

Anything mankind could come up with would be wimpy by comparison. If you disagree, you clearly haven't been put down by this year's flu. ;)

Re:At what point is a computer powerful enough?

[Carlbunn]

Bad, bad geek! There's no such thing as "too much computer power"

There is no "University of Ohio"

[illumnatLA]

It's Ohio University... Athens, Ohio not to be confused with Ohio State University an hour and a half northwest in Columbus.

Discount Quantum Dots

[EdgeTreader]

"New & used Quantum Dots. aff Check out the huge selection now" ...ebay ad running next to TFA

There is no "University of Ohio"

[Asprin]

We have The Ohio State University and Ohio University, but no University of Ohio... at least not in Ohio. [NOTE: There are a number of other state-funded Universities: Bowling Green, Toledo, Akron, Kent, Miami, Case Western Reserve, et. al., but none of them have 'Ohio' in their name, except maybe Miami, which is often called "Miami of Ohio" to distinguish it from Miami University in Florida.]

Not that big an advance.

[caffeinated_bunsen]

This only applies to self-assembled quantum dots. The ones created by lithography or otherwise manually constructed didn't have this problem in the first place. Don't get too excited (unless you're working with photoexcitation in self-assembled QDs, in which case this might matter to you).

What the hell?

[mcc]

They could be finding cures to cancer, or making better space shuttles, or doing a ton of things with applications that would be useful

Uh.. wow.

The people designing better computers aren't curing cancer because they aren't biologists. It isn't like intelligence is just something you can put in a pipe and direct it whereever you want. Some people are just better at certain things than others. Meanwhile the kinds of people who gravitate toward research fields tend to only be effective when they're doing things they find interesting and exciting. What they personally most enjoy or can best apply their talents toward may or may not be the most important thing in the world, but if it's productive and makes some sort of difference, who are we to question?

And why target the people improving computing power, and not any other "nonuseful" field? In particular, why on earth target people like the ones from this article, who are improving computing power by expanding our understanding of and ability to harness basic physics, and working in an area where discoveries potentially have direct applicability to all kinds of other nanoscale technologies, like, I don't know, smart medicines.

Even if your "couldn't they be doing something more useful" thing made sense, your examples are very poor. Better space shuttles aren't being built for a lack of ingenuity, they're being built for a lack of funding. And curing cancer in particular is a horrible example because much of the interesting expanding work in the medical research field at the moment is in bioinformatics. Meaning that cancer research would directly and seriously benefit from a major jump in the capacity of computing power, such as the one these nanocomputer people could make possible.

from the FAQ

[wud]

How do you verify the accuracy of Slashdot stories? We don't. You do. :) If something seems outrageous, we might look for some corroboration, but as a rule, we regard this as the responsibility of the submitter and the audience. This is why it's important to read comments. You might find something that refutes, or supports, the story in the main. Answered by: CmdrTaco Last Modified: 10/28/00

Re:Do we need quantum bits?

[necama]

Quantum key distribution is cryptographically equivalent to one time pads, but better -- it solves the key distribution problem; you don't need to take all the one-time pads with you when you leave.

Go watch a fleet prepare for setting to sea, and you'll see them loading one time pads onto the ship by forklift.

Out of the Physorg Tarpit ORIGINAL ARTICLE

[argent]

Is there some relationship between /. and PhysOrg? If so, Commander Taco should be ashamed of it... PhysOrg is an eyeball tarpit, it NEVER credits the original article or provides a link back to it. Never. Not once. It might as well be dead trees...

Here's the original article at Ohio University without the PhysOrg spam.

Re:Do we need quantum bits?

[wass]

That is, using quantum stuff as a new mechanics for our current paradigm, instead of coming up with a new paradigm that actually utilizes quantum properties fully.

That pretty much is what researchers in quantum computing are trying to do, it's a whole different ballgame. For example, In classical computing, 3 bits lets you put a system into exactly one of 8 (2^3) distinct states. However a quantum computer with 3 qubits will let you put the system into a superposition of these eight states, such that the superpositiong (ie, wavefunction) is properly normalized.

Quantum mechanics works in a whole different mathematical basis (Hilbert Space or Fock Space). The algebras of these spaces is quite different from classical computing, so yes, it's going to be a whole new way of looking at computing, at least at the lowest level.

On a side note, it sounds like you have just read some Thomas Kuhn, as per your frequent usage of 'paradigm', along with comparing 'evolution' to 'revolution'.

We first mentioned this six years ago...

[jea6]

We first mentioned this six years ago...

How absurd and inanely pretentious. It's astounding that the search engine the editors are using allows them to say "it's a dupe from six years ago" but not be able to recognize the dupe from yesterday. Sheesh.

Star Trek?

[jpop32]

Doesn't the article read just like your typical Star Trek plot?

You have a noble experiment:
Nanoscientists dream of developing a quantum computer, a device the size of a grain of sand that could be faster and more powerful than today's PCs.
So, after they have
blasted the quantum dots with light to create the quantum mechanical state
they encounter the problem:
they couldn't consistently control that state
So, the science officers get the work and after some time the find out the cause of the problem:
the wetting layer caused interference, instead of allowing the light to enter the dot and trigger the quantum state

And, after some hard thinking Wesley Crusher...
suggests that scientists could tweak the process by re-focusing the beam of light or changing the duration of the light pulses to negate the effects of the wetting layer!

And the day is saved.

some basics of semiconductor nanocrystals

[bodrell]

This seems to be as good a place as any to try to clear up some misunderstandings. The company where I work is trying to hire a bunch of experts in Quantum Dots, and I've seen probably a dozen presentations from different researchers applying for jobs in the past six months.

First, I know the terms Q-dots is a trademark, and I think "Quantum Dots" might be trademarked by the same company. So don't give them so much mindshare, since that company isn't really even on the "forefront" of the technology. Call them fluorescent semiconductor nanocrystals, because it actually describes what they are, so people won't think they're being used in quantum computing (not yet, at least).

Second, these nanocrystals blink. Every researcher I've seen speak about these things mentions the blinking, but only recently did I hear someone give an explanation: poor surface coating allows electrons to leak out of the the crystal.

Third, Semiconductor nanocrystals are made of several layers. The central layer is usually Cadmium Selenide (CdSe), coated by Zinc Selenide. The second coating has a higher band gap energy, so electrons get "stuck" inside the nanocrystal and then emit photons when they drop back to the ground state. Unfortunately, these nanocrystals are very sticky without more coatings. Often a PEG (polyethylene glycol) linker is stuck on the outside of the ZnSe surface to inhibit these non-specific binding events.

Last, semiconductor nanocrystals are cool because you can excite them at many wavelengths, but the emitted photon's wavelength (color) depends on the size of the crystal being illuminated. The bigger the crystal, the redder the emission. That makes them size tunable, and easily multiplexible. Eventually, that could be really useful for quantum computing (or digital video, possibly).