Both hawks and doves should be interested in this topic. We would be dangerously naive and irresponsible if we didn’t think about this topic, starting at the early stages of QC development.
Since the dawn of civilization, science has been used to design weapons, the instruments with which we defend our nation, wage war against other nations, kill and maim. Many highly successful, peaceful applications of science were initially invented or improved with warfare in mind. A modern example is the internet, which was initially funded by DARPA.
Unless humans learn to stop killing each other, which is highly unlikely, it’s inevitable that eventually, someone somewhere will use quantum computers to build weapons. So, what types of weapons could be built with quantum computers? Some obvious near term military applications of quantum computers are
cryptographic decoding – Thanks to Shor’s algorithm, quantum computers can decode efficiently certain types of cryptographic codes such are RSA, which is the backbone of our current commercial encryption systems. Luckily, there are other known classical cryptographic codes which cannot be decoded by a QC.
AI/pattern recognition – Bayesian network methods (a subset of which is MCMC (Markov Chain Monte Carlo) methods) have numerous, wonderful, peaceful applications. Nevertheless, Bayesian network methods have military applications too. For example, they are already in use (or their use is being tested) to discriminate between missiles and decoys in Star Wars defense systems. (I know this for a fact, since I was once interviewed (and rejected 🙂 ) for a defense job to write Bayesian net software for this purpose). We will soon know how to do B. net calculations on a quantum computer. (See my previous posts about quantum simulated annealing). QCs will perform such calculations much faster than classical computers. The speed at which one can perform discrimination is crucial for defensive systems like a Star Wars defense shield.
Bioinformatics – A frightful possibility in the not too distant future is bio-engineered terrorism or accidents. Suppose someone were to engineer a very harmful germ and unleash it upon us. Bioinformaticists might be enlisted to analyze this germ, as their findings might help to find an antidote. Clearly, how long it takes to analyze the germ is critical in this scenario. One common tool in bioinformatics is MCMC, so if MCMC can be performed faster with a quantum computer than a classical computer, that would help bioinformaticists do their job more quickly.