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Programmable Quantum Computer Created

Posted by Soulskill on from the four-out-of-five-ain't-bad dept.

An anonymous reader writes "A team at NIST (the National Institute of Standards and Technology) used berylium ions, lasers and electrodes to develop a quantum system that performed 160 randomly chosen routines. Other quantum systems to date have only been able to perform single, prescribed tasks. Other researchers say the system could be scaled up. 'The researchers ran each program 900 times. On average, the quantum computer operated accurately 79 percent of the time, the team reported in their paper.'"

1 of 132 comments (clear)

  1. Re:79% accuracy ... by chhamilton · · Score: 4, Informative

    No, it's actually a perfectly reasonable idea. Consider running the device (n+m) times. The probability of it being right n times and wrong m times is given by:

    P(n,m) = (n+m)!/n!/m! 0.79^n 0.21^m

    Now consider the probability of it being right (majority has the right answer) out of 2n+1 trials. This is the given by:

    S(n) = sum( P(n+1+i,n-i), i=0..n )

    This can be simplied to a closed form using Legendre and gamma functions, but that's kind of messy and it's far easier to just plug in values and do the summation. As it turns out, doing the experiment 15 times and taking the majority (plugging 7 into S(n)) will give you the correct answer 99.4% of the time. Doing things 35 times gets you to five nines of accuracy... completely reasonable in my books.