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Opening Quantum Computing To the Public
director_mr writes "Tom's Hardware is running a story with an interesting description of a 28-qubit quantum computer that was developed by D-Wave Systems. They intend to open up use of their quantum computer to the public. It is particularly good at pattern recognition, it operates at 10 milliKelvin, and it is shielded to limit electromagnetic interference to one nanotesla in three dimensions across the whole chip. Could this be the first successful commercial quantum computer?"
I work with the IQC, we specialize in quantum computing, quantum crypto, and many other things like that. We are also joined partially with the Perimeter Institute (and they do mostly theoretical physics). Anyway, when I first joined the institute, we had a discussion about d-wave. No one believed that it was real, and in fact considers d-wave to be bad for the field. Many of you will probably remember the cold fusion controversy. What happened was that experiment that could not be reproduced was published. This enraged the scientific community. Also, this led to massive funding cuts, and killed off the field. QC has a more stable base, but if d-wave keeps on been publicized like this, and they can never prove their claims (remember that all the experiments and functioning of the QC are considered "trade secrets", they let no one look at it), then we may end up with skepticism from the funders. Keep in mind that the ones who donate have usually no clue what is happening in the field (politicians, ceos, etc, so they are "stupid" enough to be affected by this. Everyone in the field is in the back of their head hoping that its real, but with that chance being so low, we want d-wave to be forgotten.
The simplest example of a quantum computing algorithm is Deutsch's algorithm.
Here is how it works. Consider a simple boolean function b_out = f(b_in). It takes an argument that can be 1 or 0 and returns a 1 or 0. There are four possibilities: always zero, always 1, the identify, and logical not.
Now imagine that I give you a black box that computes 'f'. However, it is very, very slow --maybe internally it is computing some NP-complete problem. If you want to know which of the four functions the box calculates, you need to run it twice, once for zero and once for one.
However, suppose you simply want to find out whether zero and one map to the same or different values, i.e., the parity of f. With classical computers, you are screwed. You still have to run the box twice to find that even though you only want to get a single bit of information.
However, you can do better if the black box I gave you is a quantum implementation of f(x). By feeding in a input state that is a superposition of 0 and 1, I can detect in a single evaluation plus some simple operations whether the function is constant or not. However, in doing so I get no information about the specific value. Effectively I can ask any one-bit question about f(x) as efficiently as a specific value.
It unlikely this will every be useful as stated. While it is known how to efficiently translate every classical computing algorithm into a quantum version it is unlikely a real implementation would be within a factor of 2 in speed or cost. I believe it illustrates the basic idea. The character of other quantum algorithms is similar, you often feed in a superposition of all possible inputs and read a single output which is the specific answer you want with high probability without having to ever compute the values you don't want.