Today's Quantum Optics lecture is about quantum computing experiments, and how different types of systems stack up. Quantum computing, as you probably know if you're reading this blog, is based on building a computer whose "bits" can not only take on "0" and "1" states, but arbitrary superpositions of "0" and "1". Such a computer would be able to out-perform any classical computer on certain types of problems, and would open the exciting possibility of a windows installation that is both working and hung up at the same time.
There are roughly as many types of proposed quantum computers as there are people working on quantum computation. It's not clear which of them, if any, will eventually prove to be useful, meaning that this is the perfect subject for a blog poll:
While this is a poll about quantum computing, the machines running the poll are strictly classical, so you can only choose one option.
Physical Science
Information Science
Comments
Objection: this poll is premature. I have no basis, rational or otherwise, for choosing an option. Since I'm not a specialist in this area, I don't know enough to properly evaluate the choices myself, and since I am not a high level NSF or NIST bureaucrat, I cannot appoint a flunky to evaluate the options for me.
Try again in five or ten years.
Posted by: Eric Lund | November 6, 2009 9:32 AM
I guess ion traps have been making the most impressive progress in the past couple of years, although I suspect a breakthrough in solid-state technologies could result in them overtaking ion traps at some point in the future. I am not hopeful about solid state NMR at the moment, since there seems to be a long way to go to get to the same place we were at with liquid state.
However, my main thought is that the implementation that is successful is not going to be based on the usual circuit model because error correction seems to be harder in this model than in some others. If we ever manage to construct the anyonic systems used in topological quantum computing then I would bet on that, since it seems to be automatically robust against decoherence, but since we haven't seen anyons yet it is a longshot. However, there have also been some quite encouraging error-correction threshold results in the measurement-based model over the past few years that indicate there may be a higher error tolerance than in the circuit model. Thus, I will bet on atoms/ions trapped in optical lattices because that is the most well-worked out proposal for the measurement-based model.
Posted by: Matt Leifer | November 6, 2009 9:55 AM
My objection is that I don't think there will be one single QC implementation that wins. Rather, I think we'll see different implementations for different applications, according to their advantages and disadvantages.
Posted by: Chris Granade | November 6, 2009 10:42 AM
I voted for "never a practical ..." It depends of course on what practical means. I choose to interpret it to mean that a QC could at least replace my desktop. As said in #2 I think the decoherence/error correction problem could prevent a truly practical QC in this sense
Posted by: bobh | November 6, 2009 12:03 PM
I expect great things from the research into using cats inside boxes for quantum computing that Emmy will fund from her book royalties.
Posted by: David Owen-Cruise | November 6, 2009 12:36 PM
Eric@1:
So in five to ten years, you'll be a high level NIST/NSF bureaucrat?
Posted by: Jamie | November 6, 2009 12:38 PM
Never practical, because an upper limit on number of independent qubits will manifest in the form of unwanted "incidental coherence" between excess qubits.
You'll try to calculate with an input vector representing {0-255}, but bits 3-7 will be unintentionally coherent upon creation and you're actually just computing over {0-7,248-255}.
Posted by: Anon28 | November 6, 2009 1:21 PM
I interpret "practical" as meaning a replacement for a desktop compute engine (volume of 10 to 20 L) or something that is the size a netbook or iPhone with teraflop computing speed, so I say "no".
However, I do see the possibility of a "building full of electronics" sized computer (think ILLIAC or CDC6000 series) that serves a specialized purpose worthy of its cost.
Posted by: CCPhysicist | November 6, 2009 2:03 PM
I voted for "undiscovered."
In computing, progress = smaller. So the technology will probably be molecular. Possibly implementing one of the listed technologies at the molecular level.
Posted by: Bob Hawkins | November 6, 2009 2:43 PM
Never practical as I think it highly unlikely you can set up arbitrary many independent superpositions of identical qbits occupying a small space. I expect interference to manifest itself when enough of them are packed close together.
Posted by: Z | November 6, 2009 4:27 PM
Why is everyone equating "practical" with replacing their current laptop or desktop system? Of course, I realize that I may look as silly as a certain head of IBM for saying this, but, as it stands, there are no applications of quantum computing that would be relevant to the world of personal computing, except perhaps crypto, which doesn't require a quantum computer anyway. Anyway, I think we should interpret "practical" as "every big university and pharma company has one that is routinely used to simulate the quantum properties of molecules". At least if we get to this point then it is a good bet that a quantum equivalent of Moore's law will kick in and we could make them smaller if necessary.
BTW, in my previous comment I should have said non-abelian anyons instead of just anyons. The abelian ones have been observed in the fractional quantum Hall effect, but we need the non communtative ones for QC.
Posted by: Matt Leifer | November 6, 2009 6:54 PM
I have a master Venn diagram, annotated, with my take on this. I have scanned it as a PDF. I can email the PDF to Dr. Chad Orzel if her requests, otherwise I'll just keep it with my other 500,000 pieces of paper with ink on them, in my overflowing 11-room hyper-academic home/garage/storage shed...
I do have several refereed works on Quantum Computing published, but it's always nice to boil things down, as this blog thread intends.
Posted by: Jonathan Vos Post | November 7, 2009 5:19 PM
I mean "if HE requests" -- I was making no insinuation about a quantum mixed state of gender, as recent data is reasonably unambiguous. I make no jokes about balls as Bloch spheres.
Posted by: Jonathan Vos Post | November 7, 2009 5:21 PM
I bet on Q C processor constructed from a can of supercooled maraschino cherries which have their pits removed so as to keep their spins from colliding
Posted by: milkshake | November 8, 2009 7:29 AM