The qubits entangle

Posted on Saturday, October 2nd, 02010 by Alexander Rose - Twitter: @zander
link Categories: Long Bets, Technology   chat 0 Comments

Nature reports quantum computing researchers achieve “success at entangling three-circuit systems”.

“The entanglement of two or more qubits sets up a ‘superposition’ of states in which calculations can run in parallel — in principle allowing a quantum computer to race through problems that it would take a classical computer eons to solve. Such a quantum machine would require hundreds or even thousands of entangled qubits. The maximum reached so far is 12, but some of the systems that researchers are working with, including those depending on the spins of ions, may be hard to scale up.” [read the story]

While this is progress it does not look like we are on the road to having a commercially available 100 qubit machine by the end of 02010 as predicted on Long Bets:

There will be a quantum computer with over 100 qubits of processing capability sold either as a hardware system or whose use is made available as a commercial service by Dec 31, 2010

Looks like this is a good prediction, but just a few years off.

  • That Long Bet is too imprecise to make sense. How should one determine whether or not a supposed quantum computer is really quantum computing? There is, unfortunately, no widely-accepted, unambiguous gold standard for answering this question anywhere in the scientific literature.

    As an example to illustrate the problem, the company D-Wave Systems have publicly claimed to have a working 128-qubit quantum computer. Unfortunately, very few researchers in the field believe their claims. Should the Long Bet be awarded on the basis of D-Wave's claim? It's not at all clear who should decide the status of the bet, and on what basis they would make a decision.

    More generally, for any experimental system it's hard to say exactly how one should decide whether it's doing a quantum computation. The essential problem is that all the operations done in any putative quantum computer are only ever approximations to the ideal operations that we'd like to have implemented. And so the question is: how good does your approximation to the ideal need to be, before you can reasonably say you're performing a quantum computation?

    Now, in practical situations there's often pretty good rules of thumb that can be used. There's a procedure called quantum process tomography which can be used to characterize just how well a quantum gate has been performed. And for more complex quantum computations there are other rules of thumb that work pretty well in practice. But it's a subtle issue.

    (Some background: I worked full-time on quantum computing between 1995 and 2007, and co-authored the standard text on the subject.)

navigateleft Previous Article

Next Article navigateright