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First Evidence That Google's Quantum Computer May Not Be Quantum After All
KentuckyFC writes "In May last year, Google and NASA paid a reported $15 million for a quantum computer from the controversial Canadian start up D-Wave Systems. One question mark over the device is whether it really is quantum or just a conventional computer in disguise. That's harder to answer than it sounds, not least because any direct measurement of a quantum state destroys it. So physicists have to take an indirect approach. They assume the computer is a black box in which they can input data and receive an output. Given this input and output, the question is whether this computing behavior can be best reproduced by a classical or a quantum algorithm. Last summer, an international team of scientists compared a number of classical algorithms against an algorithm that relies on a process called quantum annealing. Their conclusion was that quantum annealing best reproduces the D-Wave computer's behavior, a result that was a huge boon for the company. Now a group from UC Berkeley and IBM's Watson Research Lab says it has a found a classical algorithm that explains the results just as well, or even better, than quantum annealing. In other words, the results from the D-Wave machine could just as easily be explained if it was entirely classical. That comes on the back of mounting evidence that the D-Wave computer may not cut the quantum mustard in other ways too. Could it be that Google and NASA have forked out millions for a classical calculator?"
I am at such a loss of understanding what exactly quantum computers are and how they work (no matter how hard I try)... so it makes me feel like less of an idiot when I find out that it's so complicated that even Google engineers aren't even sure if what they have IS one.
Do we really think that D-Wave Systems would take that risk? They have to know that just about every major university and tech company will try to prove them wrong. Not to mention that Google will probably spend more to verify this purchase than they made on the purchase itself.
I don't know D-Wave Systems from Adam, but is this a risk they would take?
Maybe it simultaneously both is and isn't a Quantum computer? :-P
Lost at C:>. Found at C.
Why buy something that isn't demonstratively faster than the old stuff
Research often requires baby steps. If you ignore every new idea whose first (or hundredth!) iteration isn't already better than what we have, you'll ignore every new idea.
Note to ACs: I usually delete AC replies without reading them. If you want to talk to me, log in.
Before this research, it was demonstrably faster at some things, and slower at things a quantum computer is not good at. So they did exactly what you expect.
I have a device for sale which generates free, unlimited power. The catch is that you cannot measure the power output or it won't function. If you put any load on the device you are directly or indirectly measuring the power, and thus it won't work. So just know up front that stipulation and use the device accordingly.
Better known as 318230.
Quantum effects are not hard to understand, they're just counter-intuitive to everyday experience. This site has a good explanation of QM, and how it differs from normal experience.
The universe doesn't work in specifics until something is measured. It doesn't choose parameters for particles (spin, position, &c) at the outset and let things evolve like little billiard balls.
Instead, it uses probabilities which flow and interact with one another. These probabilities have both amplitude and phase, so that the interactions are wave-like as well as probability-like. For example, because of this wave-like interaction it's possible for two non-zero probability flows to completely cancel to zero.
The universe appears to calculate probabilities for all possible outcomes and only choose one when the measurement is made. When particles are entangled, you increase the number of possible outcomes. For each new particle that becomes entangled you increase the number of possible outcomes by a factor of two. Ten particles will have 2^10 = 1024 possible outcomes, and so on.
So to do math at the quantum level, you take a set of entangled particles and set up the measurement so that division with no remainder has probability one while division with any other remainder has probability zero. Then load your register with all the integers, let the probabilities interact, and take the measurement.
You have just performed division using all the integers at once.
If you can do this with a reasonably large register you can check all the factors of a composite number in linear time - the time it takes you to load sqrt(P) divisors into the register.
Easy peasy!
An interesting side-note is the idea of the universe keeping track of all possible outcomes until a measurement is made. If this works as predicted, the universe will have to keep track of 2^3000 possible outcomes, depending on the key length (3000 is the recommended RSA key length to be secure until 2030).
There are only ~10^80 = 2^240 atoms in the universe. If a quantum computer works as predicted, one wonders how and where the universe keeps track of all these states. At the very least, quantum computing is interesting because it will allow us to probe the limits of the universe in an entirely new domain.
Here's hoping we don't encounter a buffer overflow.
(Note: Some facts were harmed in the making of this explanation.)
Why buy something that isn't demonstratively faster than the old stuff...
I mean if the difference is so small that there is some sort of debate about if it is effectively working or not, then it seems to me at that point cost should be the deciding factor. I doubt these D Wave machines are any cheaper than the old stuff.
Part of the problem has been D-Wave's confusing abuse of terminology:
1) They claim their device is a computer, but it's not according to the usual definition (a Turing machine with bounded tape (RAM)). It's more similar to an ASIC (application-specific integrated circuit).
2) They claim their device is a quantum computer, but it's not according to the usual definition (a device which requires quantum phenomena to operate). There is some evidence it uses quantum effects, but they don't appear fundamental to its operation (otherwise we wouldn't be having this quantum-or-not merry-go-round).
3) They claim their device solves its (application-specific) problem 35,000x faster than a classical machine, but in fact they had programmed the classical machine with a much harder problem (finding an exact solution, rather than an approximate one). When a classical computer was programmed to solve the same problem as D-Wave's machine, the classical machine was faster.
4) They consistently conflate quantum algorithms (algorithms inspired by quantum mechanics) with quantum computing (which requires quantum mechanics to operate). Their machine implements a 'quantum simulated annealing' algorithm, but this doesn't require a quantum computer to run. Likewise, a regular 'simulated annealing' algorithm doesn't require a heat engine to run. Likewise a 'genetic algorithm' doesn't require a DNA-based computer to run.
5) They keep moving the goalposts to remain as impressive-but-vague as possible. Rather than showing definitive results to back up their claims, they keep making claims then weakening them afterwards when researchers show them to be false. This is like an inverse No-True-Scotsman; academics have a clear definition of what a quantum computer is, and D-Wave keep trying to expand that definition it to include their machines.
In short, Google and NASA bought their machines when there were claims bouncing around about 35,000x speedups, but these were subsequently found to be flawed.
I'm all for investing in basic research, but it often looks like D-Wave's research output is coming from their marketing department rather than their scientists and engineers :(