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Solid State Quantum Computer Finds 15=3x5 — 48% of the Time 262

Posted by timothy
from the please-show-your-work dept.
mikejuk writes "The Shor quantum factoring algorithm has been run for the first time on a solid state device and it successfully factored a composite number. A team from UCSB has managed to build and operate a quantum circuit composed of four superconducting phase qubits. The design creates entangled bits faster than before and the team verified that entanglement was happening using quantum tomography. The final part of the experiment implemented the Shor factoring algorithm using 15 as the value to be factored. In 150,000 runs of the calculation, the chip gave the correct result 48% of the time. As Shor's algorithm is only supposed to give the correct answer 50% of the time, this is a good result but not of practical use."
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Solid State Quantum Computer Finds 15=3x5 — 48% of the Time

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  • by TheRaven64 (641858) on Sunday August 26, 2012 @11:57AM (#41129601) Journal
    Validating the result is cheap on a classical computer. Even for very large values, multiplying two 4096-bit values together and checking the result is incredibly cheap. A quantum computer that could give the right set of divisors for a 4096-bit prime 1% of the time would still let you very quickly find which of the answers that it gave was correct. The limitation is the size, not the reliability.
  • by IamTheRealMike (537420) <mike@plan99.net> on Sunday August 26, 2012 @12:10PM (#41129719) Homepage

    It seems that quantum computing has consistently been viewed as harder than it really is, judging by the ever-decreasing timescales between breakthroughs. Judging from the history of cryptography, and the military value of being able to break RSA, it's not unreasonable to expect that the NSA may have been trying to build such a chip for some time and could potentially have succeeded.

    Some months ago James Bamford, who is the premier chronicler of the NSA and has a history of being given accurate leaks, claimed the NSA had made a "huge breakthrough" in its ability to break codes [wired.com] - and that the datacenter they're currently building is a part of the solution. The NSA denied everything of course. But if academics are now able to build a working implementation of Shors algorithm for small numbers, that strongly implies that a focussed team with practically infinite budgets could have already succeeded in building one that can handle crypto-sized numbers.

  • 50% of the truth (Score:2, Interesting)

    by OzPeter (195038) on Sunday August 26, 2012 @12:26PM (#41129797)

    Could it be that the reason the algorithm is only supposed to get the rich answer 50% of the time is that there is a parallel universe out there where 5 x 3 is not 15???!?!?

  • by Shavano (2541114) on Sunday August 26, 2012 @12:43PM (#41129905)

    That may be so, but computing the prime factorization of 15 is not in that class.

    I don't think you should even get to call something a middle-school dropout can figure in his head faster than he can say "Fries with that?" computation. So-called quantum computers still barely qualify as expensive but useless toys.

    Post again when a quantum computer can solve a real mathematical puzzle at a speed comparable to what a traditional computer can do. That would be news.

    Scientists have been touting the supposedly vast potential of quantum computing for decades now. D-E-C-A-D-E-S. But thanks to fundamental limitations of the nature of what they are, it's really hard to get them to barely work at all. It appears we could forever be stuck at the point where the qubits can be minimally processed but quantum decoherence can't be held off long enough to get a useful result. Meanwhile traditional methods of computing continue to forge ahead, although the rate of increase is slowing. Just keep in mind: quantum computing is 2500 years behind traditional computing methods in general, 175 years behind automated mechanical methods and more than 70 years behind electronic computers.

    Electronic computing methods overtook all other methods extremely quickly, but they faced only technical challenges not challenges posed by the fundamental nature of what they were trying to do. You can regard them in some ways as fancy abacuses: they literally count chunks of charge the way an abacus uses the position of beads to represent numbers (or in principle anything else). With qubits, you are attempting to get definite results by exploiting the indefinite character of things like the spin states of electrons. That's not just hard. It may be intractably hard. But if somebody can get it to work it might be very valuable to the NSA and anybody else interested in cracking the security of computing systems.

  • Re:Maths (Score:1, Interesting)

    by lordmetroid (708723) on Sunday August 26, 2012 @04:56PM (#41131593)
    Why is this anonymous coward moderated funny. The anonymous should be moderated insightful cause it is correct that for very large number of two. 2+2=5. Let me demonstrate:

    By writing 2+2=5, we merely have one significant digit of precision. It is very possible that the 2s are for example 2.4 or 2.1 or whatever number which would be rounded down to 2 when written with a one significant digit.

    Imagine that the twos are actually 2.4999... which when added together would be 4.999... As we are only have a single digit of precision we are forces to round that to 5. Hence we have proved that 2+2=5 for very large numbers of 2.
  • Great! Congrats! (Score:5, Interesting)

    by drolli (522659) on Sunday August 26, 2012 @04:58PM (#41131609) Journal

    Disclaimer: I am a former researcher in the field, left to some other job.

    What you can see at UCSB is what happens when a team of scientists which ae skilled in engineering, working as a team, and collaborating with everybody happens to have the right guy as the leader (with the right policy about co-authors on publications).

    Everybody whom i met from this team was open, honest, and friendly; they have worked hard and long on it and they accumulated some of the best people.

    They deserve the success they have now! I think there may be a small break now in their publications, since i have the ffeling they now may work on overcoming the next big roadblocks (but now they they have all the backing they could need for it).

    I also have to state it will be a long long way to the first QC. While i believe that every step like this will be more than just replicated at the NSA, i believ that they wont be more than 10 years ahead, and i estimate 20y-30y until qc works better than classical qc (although I also hope and believe that breaktroughs are possible).

Imitation is the sincerest form of plagarism.

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