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Qutrits Bring Quantum Computers Closer

Posted by kdawson on Fri Apr 04, 2008 10:46 AM
from the shortcut-through-higher-dimensions dept.
Supercomputing Science
KentuckyFC writes "To do anything useful with quantum logic gates, you need dozens to hundreds of them, all joined together. And because of various errors and problems that creep in, that's more or less impossible with today's technology. Now an Australian group has built and tested logic gates that convert qubits into qutrits (three-level quantum states) before processing and then convert them back again. That makes them far more powerful. The group says that a quantum computer that might require 50 conventional quantum logic gates can now be built with just 9 of the new gates. What's more, the gates process photons using nothing more than standard linear optical components (abstract on the physics arxiv)."
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Submission: Qutrits bring quantum computers closer by KentuckyFC (1144503)
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  • Throughout the heyday of personal encryption, when Zimmerman was maintaining PGP and Bruce Schneier's Applied Cryptography [amazon.com] was released, we kept hearing about how it would take thousands or millions of years to crack just one PGP message. Now we hear that computers that could break these messages might be relatively just around the corner. It's got to be a real disappointment and source of worry to people who did use PGP to encode the secrets that they are desparate to hide.
    • don't be silly, no one gives a shit what 99.99% of people here sent using PGP. Governments, banking system, financial markets, megacorps will be the ones to worry.
    • Yes and no. I mean, the problem that you point out is only exists because a quantum computer is cracking an encryption that had to run in reasonable time on today's computers. But quantum computers don't have to be just one way like that... now you would have at your disposal a computer that can run encryption that would take thousands or millions of years on todays machines, on your data.
    • Somewhat. Private key schemes are still secure.

      The real power of quantum computing will be in factoring primes. Which most certainly will affect public key crypto, but public key was never the FULL solution. Like anything in crypto different problems have different solutions.

      Public key crypto is great in the web age because you can use it for establishing connections, exchanging private keys, etc.

      One of the first things you learn in any crypto grad class is that creating the crypto schemes is only part o

    • Now we hear that computers that could break these messages might be relatively just around the corner.

      (Emphasis added)

      You might die tomorrow. Hurricanes might devastate the western world. Aliens might show up and blow the planet to bits for housing such a greedy, self-centred species. Any number of progressively unlikely things might happen.

      There's no real substance to the rumours of encryption-defeating quantum computers - it's a hypothesis somebody proposed a few years ago, which has never been proved or

    • we kept hearing about how it would take thousands or millions of years to crack just one PGP message.

      What were you reading?! Everything I ever read stressed the fact that there was something on the order of a 10-50 year expectation of privacy on anything you protected with current encryption mechanisms. That has pretty much been proven out, given that we're now on year 20 since I started using public key crypto.

      As for quantum computing: don't get your hopes up. There's no proof of concept that shows that QC will ever scale up to practicality. Every 6 months someone announces a "breakthrough" and gains ple

    • The limit for quantum computing is currently space, the number of qubits you can keep at the same time is still very limited and AFAIK current QCs don't have the space to store a 2048 bit key.
  • Does it run linux?
  • Naturally, I read that as "qutits" the first time.

    • Re: (Score:1, Funny)

      by Anonymous Coward
      Qutrits, just like the chick on "Total Recall."

    • Just as the hard-wiring of binary mathematics spun the entire twentieth century about a simple yes-no axis, the invention of the three-state switch promised to revolutionize twenty-fifth century computing. After all, with three states (negative, positive, and null charges) on nanoswitches, computers could now think in terms of yes, no, and maybe, greatly humanizing their internal logic.

      This would have brought many, many more female engineers into the field of computer science (hence accelerating the pace at which computers could do useful things besides transmit, compress, and enhance pornography), except that the same abbreviational logic that turned "binary digit" into "bit" turned "trinary digit" into "tit." This nomenclatural error set computing back nearly three hundred years, and two entire generations of promising computer scientists were lost trying to keep abreast of bad puns.
      Courtesy of the genius at Schlock [schlockmercenary.com]
    • qutits, much more powerful than conventional tits... uuuuuhm.. bits...
    • I read it as qutris. Quantum Tetris would be... weird.
  • Give the computer a nice cup of hot tea. From Douglas Adams "The Hitchhiker's Guide to the Galaxy" "If he thought to himself, such a machine is a virtual impossibility, then it must logically be a finite improbability. So all I have to do in order to make one is to work out exactly how improbable it is, feed that into the finite improbability generator, give it a fresh cup of really hot tea...and turn it on!"

  • What it means (Score:4, Informative)

    by usul294 (1163169) on Friday April 04 2008, @11:05AM (#22964272)
    What this is basically saying is that instead of operating a quantum computer with 2 levels, 0 and 1, they are operating with 3, 0,1,2 lets say. According to my computer architecture prof 3 levels is the most efficient way of making computers, from a number of components standpoint. Its hard thinking in base-3, because things like inverters become meaningless. AND and OR gates still work with a reasonable amount of understanding. Things like multiplexers and decoders make sense. If you can get into the macroscopic level of design its pretty understandable. You can use 3 trit words to do base-27 in a similar way to using 4 bit words and hex.
    • Interesting, why is base-3 more efficient than base-2? I seem to recall that the dropoff was base-4 but I don't recall any real net advantages to base-3.

      • Re:What it means (Score:5, Informative)

        by mblase (200735) on Friday April 04 2008, @12:42PM (#22965576)

        Interesting, why is base-3 more efficient than base-2? I seem to recall that the dropoff was base-4 but I don't recall any real net advantages to base-3.
        It's called ternary logic [wikipedia.org], and it's been widely researched if rarely implemented. It seems to be built on the notion that a thing can be true, false, or unknown/irrelevant.

        Think of an SQL database, where a field can be TRUE or FALSE; however, if you didn't set up default values, it can also be NULL, neither true nor false. Or in mathematics, where a value can be GREATER THAN, LESS THAN, or EQUAL TO -- three mutually exclusive states. These aren't circuit-based examples, but it does illustrate how ternary logic can be routinely applied.

      • Re: (Score:2, Interesting)

        by lenester (625236)

        Interesting, why is base-3 more efficient than base-2?
        Because 3 is closer approximation of e [wikipedia.org] than 2.
    • ARGH! I'm too embedded in binary logic, I can't really understand how you could make base-3 AND or OR gates. Like for example: 0 AND 0 = 0 0 AND 1 = 0 0 AND 2 = 0 1 AND 1 = 1 1 AND 2 = 1 2 AND 2 = 2 0 OR 0 = 0 0 OR 1 = 1 0 OR 2 = 2 1 OR 1 = 1 1 OR 2 = 2 2 OR 2 = 2 Where 0 means no, 1 means maybe, and 2 means yes?
      • Grr, html...
        0 AND 0 = 0
        0 AND 1 = 0
        0 AND 2 = 0
        1 AND 1 = 1
        1 AND 2 = 1
        2 AND 2 = 2
        0 OR 0 = 0
        0 OR 1 = 1
        0 OR 2 = 2
        1 OR 1 = 1
        1 OR 2 = 2
        2 OR 2 = 2
        Where 0 means no, 1 means maybe, and 2 means yes?
    • Bender: And I think I saw a 2!
      Fry: Don't worry, there's no such thing as 2.

      There's a lot of different ways to use the extra value. If you treat it as "unknown", or the logical equivalent of NaN, then you can do NOT, AND, and OR with 0's and 1's, then use 2 as an exception case that can propagate.
    • Of course you'll have to program it in TriINTERCAL...
    • Of course, this being a quantum circuit, there is the added complication of the fact that a single qutrit can be in a superposition of any and all three of those levels.
  • Finally some games coming out for the quantum computers. I can't wait to see what Alexey Pajitnov would have done with this hardware.
  • So does this mean that quantum computing will be based entirely on trinary code? Will those conceptual/theoretical trinary programming languages finally get some time in the sun?
  • What I want to know is... when do we get a quantum computer based on Quatloos?! [quatloos.com] And can you imagine a Beowu... never mind!

    • A qubit with three tits .. err.. i mean bits (I should have said states but bits rhymes better)
  • Qutrits with optics is cool, but is the quantum computer just around the corner? Most definitely not! Optics are great for communicating quantum information, not so much for storing them. Quantum memory needs solid state technology, and while some promising results have been reported using diamonds by researchers at Harvard [harvard.edu] and other places, the quantum computer is still many many years, maybe even decades away. TFA is overhyped, as seems to be the case with all articles reporting quantum computing breakthr

  • Now an Australian group has built and tested logic gates that convert qubits into qutrits (three-level quantum states) before processing and then convert them back again. That makes them far more powerful.

    I'm a visionary!

    3-State Bit [slashdot.org]

  • Asin trinary? 0, 1, dead cat?
  • Bah! Back when I was a kid we had only two logic states and we were happy to have them!

    • ...quantum logic gates...logic gates...qubits...qutrirts...quantum states...quantum computer...quantum logic gates...gates...gates...photons...linear optical components...

      For some reason, this reminds me of this post [xkcd.com] on about blogs [xkcd.com] on xkcd.

    • Re: (Score:3, Informative)

      by CogDissident (951207)
      A "gate" is roughly the equivalent of a transistor. Kind of. Think of it like a lot of transistors all put together.

      • Re: (Score:1, Funny)

        by Anonymous Coward
        A "gate" is roughly the equivalent of a transistor. Kind of. Think of it like a lot of transistors all put together


        And a transistor is kind of like a tube. (remember in the 1960s when they replaced all those tube radios with transistor radios?) So really, when it comes right down to it, the Internet IS really a bunch of tubes.

    • Re:Wow (Score:4, Funny)

      by peragrin (659227) on Friday April 04 2008, @10:55AM (#22964094)
      Oh it's simple. The cat could be not only alive or dead, but also could be on life support.

      Or maybe the cat will be spinning because someone stapled a piece of bread with jam onto the cat's back.

    • Re:Wow (Score:5, Informative)

      by hansraj (458504) on Friday April 04 2008, @11:20AM (#22964440)
      The word "gates" has almost the same meaning in quantum computing as in the classical computing. In classical computing a gate operates on a set of bits and changes them to another set of bits. In quantum computing it is the same with qubits playing the role of bits.

      Of course funny things are possible in quantum computing. For example it is possible to make a "square root of not" gate, that when applied *twice* to the qubit |1> produces |0> and vice versa. Applying once creates something else (the square root of not in some sense).

      One particularly handy way to think of quantum gates is to think of them as a matrix (operator) that operates on a vector (input qubit) to produce another vector (output qubit) just by multiplication. So if A is some quantum gate (matrix) and u is input qubit (vector) the the output qubit (vector) v = A*u . The matrix A needs to satisfy some technical requirements that gives quantum computing some nice features (like every algorithm is fully reversible and so on), but those details are not needed to get a rough idea. :)

      • For example it is possible to make a "square root of not" gate, that when applied *twice* to the qubit |1> produces |0> and vice versa.
        I suppose you mean that, if |1> = |0> times exp(i pi/2), for example, then that "square root of not" operator would be something like SRN = exp(i pi/4) ?

      • Re:Wow (Score:5, Informative)

        by grammar fascist (239789) <neil.toronto@gmai[ ]om ['l.c' in gap]> on Friday April 04 2008, @03:04PM (#22967240) Homepage
        Too bad I lost my mod points yesterday. This is the kind of thing people actually come to Slashdot for. I'll just have to try to contribute instead.

        Here's some further detail for those interested: the |1> and |0> qubits are actually vectors of probabilities. (Well, probability "amplitudes". More on that later.) The |0> bit means [1 0] and the |1> bit means [0 1]. The "|.>" notation is a bit of convenient shorthand.

        If you have two qubits, you'd represent them as |00>, meaning [1 0 0 0]. (That's four possibilities for the qubits, and all the probability mass on the first: both off.) |01> means [0 1 0 0], |000> means [1 0 0 0 0 0 0 0], and so on. Note the exponential growth.

        A quantum gate is nothing more than an operator of the same type that governs all discrete quantum system evolution: a unitary matrix. Think of a rotation matrix of rank 2**(number-of-bits), but in complex space. It's got to be some kind of rotation - it must preserve length - to preserve the property that the qubit states and combined qubit states are probability (amplitude) distributions.

        A "square root of NOT", IIRC, is an operator (rotation) that turns [1 0] (or |0>) into [sqrt(1/2) -sqrt(1/2)]. Do it again, and you get [0 1]. Again, and you get [-sqrt(1/2) sqrt(1/2)], and again yields the original [1 0]. (I may have some signs wrong.)

        The reason this cycle works at all is that the states aren't probabilities per se, but sort of square roots of probabilities, which allows them to keep extra information. This is called "phase". Much of the exciting weirdness of computing with quantum gates is that phase isn't strictly real, but in general has imaginary components.

        The other exciting weirdness is of the massively parallel sort. If I do a computation on [sqrt(1/2) -sqrt(1/2)], it's sort of like doing the same computation on [1 0] and [0 1] in parallel. The tricky part is that measuring the outcome restricts me to just one of the results! One way to express the dilemma is that I can compute an answer for every possible input simultaneously (which would be great for solving NP problems), but that I can't easily select the right answer.

        Another way to express it is to say that the cat is in a superposition of dead/alive, which will localize when I observe the poor beast. :)
    • In this context, it probably means something like a logic gate [wikipedia.org], although the operations on 3-state gates might be different.

    • Re: (Score:3, Informative)

      by Ctrl-Z (28806)
      I trust you read the summary. The neat thing about this is that you need fewer gates to do the operations with qutrits than with qubits. Fewer gates means that the machine is easier (or even possible) to construct. It seems to me that it is a short-term gain. As you point out, you are doing more work to achieve the same outcome, although I don't know where you pulled your numbers from. It's not a 50% increase in processing; they were able to do the work of 50 gates with a mere 9, which is a five-fold i

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