Re: Quipper: a quantum programming language

[selinger@mathstat.dal.ca (Peter Selinger)]

Dear Andre,

the answer, unfortunately, is no. At least we don't think so. We
developed this programming language for IARPA, an agency of the
U.S. government, and effectively nobody knows whether they have a
quantum computer or not.

In any case, the language is designed so that it *could* run on a
quantum computer, if there was one. So now we are just standing by
until somebody builds the hardware :)

There is actually one kind of quantum computer that is already on the
market: the DWave quantum computer. Unfortunately, our language is not
compatible with it; the DWave machine uses a technology called
"adiabatic quantum computing", and people are still figuring out how
to program it. Our language would be compatible with quantum computers
based on the quantum circuit model.

Maybe the underlying point of your question is: why would anybody care
about a quantum programming language, when there is no quantum
computer?

One possible answer is: to help figure out how much it would actually
cost to build one. It is one thing for a quantum algorithm to appear
in a research paper. You will find a lot of statements like "it is
well-known that such-and-such can be done in O(n^2) operations", "by
applying such-and-such trick this problem can be reduced to another
problem with polynomial overhead", and so on. It is quite a different
thing to actually program the algorithm, and to worry about how to do
so efficiently. The difference between using 10^10 operations or 10^50
operations matters a lot in practice, but not in theory. Moreover, one
can then account for additional overhead that people don't usually
think about much, like the cost of adding many layers of error
correction, physical fail-safe mechanisms, and so on. By coding up
some algorithms for "realistic" problem sizes, we get a much better
idea of what kind of computing resources this would actually require.
("Realistic" can be defined as the problem size where a hypothetical
quantum computer would actually outperform a classical computer
running the best known classical algorithm for the problem).

Finally, there is some interesting theory that we can discover by
considering programming languages for quantum computing. To our
surprise, we even found a minor, yet satisfying, application of
identity types from type theory.

Best wishes, -- Peter

Joyal, Andr?? wrote:
>
> Dear Peter,
>
> I would like to ask you a naive question:
>
> Is it runned on an actual quantum computer?
>
>
> Best,
> Andr??
>

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