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Quantum Programming with Perl
moyix writes: "There's an article over at perl.com that describes how to use a perl module called Quantum::Entanglement. Using this module, one can simulate programming for a quantum computer. Developers looking to keep their skills current well into the next decade should check this out ;) Debian folks can grab libquantum-entanglement-perl and libquantum-superpositions-perl."
Anyone interested in doing any type of quantum computing should check out Dr. Damian Conway's excellent Quantum::Superpositions. It is an extension to the perl language which adds the operators "any" and "all"... it's lets you do *incredible* things like:
... }
... }
use Quantum::Superpositions;
if ($x == any($a, $b, $c)) {
while ($nextval < all(@thresholds)) {
$max = any(@value) < all(@values);
A good place to go and discuss the in's and out's of the cooler aspects of the perl community is perlmonks.org, check it out some time...
Although I can't get to the article right now, I do know a little about quantum computing thanks to having just finished a thesis on the subject.
Studying the actual research in the field reveals that a real quantum device does not at all resemble a superintelligent "infinitely-faster-than-my-Pentium-4" computer of the future. To understand the difference requires understanding the fundamental nature of a quantum device and how it differs from a digital device.
The atomic unit of a quantum computer is a physical system of some sort that exhibits quantum behavior, such as a single electron and its spin. Whatever the implementation, the unit is called a qubit. A single qubit contains information sometimes described as a vector of complex numbers.
A digital computer, of course, operates on bits which allow only two states, the most common implementation of which is a high or low voltage at some defined point in an electrical circuit.
Some operations are natural and easy to perform on bits; these are AND, OR, NOT, XOR, and their Boolean friends. These operations, in turn, lend themselves to an easy and natural implementation of integer math. Other operations do not have a natural representation in digital computers, such as real-number arithmetic. For the relatively few occasions that call for irrational numbers, we make do with approximations and call it "floating-point" math.
The qubit's advantage is that, thanks to quantum mechanics, some operations which are very difficult for a digital computer are easy and natural for qubits. Notably, a set of qubits can perform a Fourier transformation in near constant time--an astounding operation that is so far believed to be impossible on any kind of Turing machine.
The other side of the coin, which is rarely understood by mainstream news reporters, is that the qubit is completely unable to address most of the rest of our favorite operations, such as integer addition. To ask a qubit to count from 0 to 9 is extremely difficult, maybe physically impossible.
If that weren't bad enough, quantum algorithms have to deal with other constraints such as the prohibition against creating a copy of an unknown quantum state. Therefore, your quantum Perl is going to have to start by doing away with the assignment operator. Qubits also have a nasty tendency to occasionally do things completely unexpected and unpredictable; this requires massively redundant calculations to reduce the probability of error to something acceptably small. (Of course digital computers suffer from random bit rot as well; it is solved with similar error detection and correction algorithms.)
All these obstacles discouraged any serious interest in quantum devices for some time. However, recently (1997?) Peter Shor published the first important quantum algorithm, which factors large composite numbers in polynomial time. In case you don't know, a computer with such a capability would have staggering implications. Much of the world's data protection is based on the RSA algorithm which relies on the difficulty of factoring large numbers.
Hence, the last few years have seen no shortage of funding or interest in quantum computing. Unfortunately, the mainstream media has caught just enough of the conversation to get the false idea that quantum computers are going to blow away all of the digital technology in existence, coming soon to a Best Buy near you.
Anyway, the moral of the story is, don't start saving for that Pentium-Q just yet; not only is a quantum device completely inappropriate for the overwhelming majority of computing tasks, but the current state of the art is a machine on the order of 10 qubits or so. (A few hundred qubits will be needed before Shor's algorithm presents a threat to current encryption.)
More realistically, you might expect to see one day in your lifetime a "quantum processing unit" that exists as a special-purpose extension to your digital processor--think along the lines of the 80287 floating point coprocessor. Even this kind of application is decades away at best.
The real use of this is for people who want to experiment with quantum _algorithms_ on small data sets and learn and understand better how quantum computers work and how quantum calculations are put together. Writing quantum algorithms is hard and confusing to somebody familiar with classical computation, even if you are familiar with quantum mechanics. There are very few useful quantum algorithms (Gover's search and Shor's factorization algorithms are the two most famous and interesting IMHO). This module might encourage more people to come up with and experiment with quantum algorithms that take advantage of the "inherently parallel" nature of quantum computing.
Note that though I am no expert, I did actually write something modestly similar to this Perl - an interpreter that read a series of meta-language commands and turned them into physical magnet pulses for spin flipping on an NMR quantum computer we had at MIT. We never bothered to write a simulator for it, but now that I think about it, it would be cool to have this. Kudos to these guys for doing this.
Now if somebody could just make a quantum computer with, say, 20 or 30 qubits I might be convinced that quantum computing could eventually do useful calculations and that the decoherence problems and setup problems for a large number of weakly coupled qubit units are not intractable. Perhaps an alternative to NMR as the substrate for quantum computing might get farther.
Another way to play around with nonclassical algorithms and get your feet wet with quantum programming would be QCL.
QCL is a procedural quantum programming language which provides nonclassical language elements such as unitary operators, running code in reverse, scratch space management, etc. A Linux interpreter (GPL) which simulates a quantum computer with an arbitrary number of qubits is available here.