Some Thoughts On Quantum Computing

Some remarks by a speaker at a recent professional event inspired me to rant a bit on the topic of quantum computing. For sure, it's not my area of expertise, but I do have a dilettante interest in quantum physics, plus I took a short course at University of Denver a few months ago that was a kind of "Quantum Computing for Dummies", and it is the area of expertise by the Ph.D. physicist who taught it.

[1] Quantum computers will not replace conventional computers. There is a lot of interest in QCs because it is believed that they can do calculations that are not feasible for today's computers. But those calculations are only possible for problems for which there are known - or believed - to be QC-type algorithms. You will never be running a web browser or a spreadsheet on a QC.

[2] One example is Peter Shor's quantum algorithm for large number factorization, which could be used to break encryption schemes that rely on the difficulty of such factorization. Shor is a theoretical computer scientist who developed Shor's Algorithm while at Bell Labs. This is why governments are interested/concerned about QC. A lot of encrypted secrets have been stolen by hackers (theirs and ours), but are just useless bits until they can be decrypted.

[3] Not all encryption is based on large number factorization. Maybe there are as yet undiscovered QC algorithms for the "trap door functions" that those schemes use instead of large number multiplication and factorization. Maybe not. Until then - if ever - such schemes are described as quantum resistant. Switching to such schemes is probably a good idea for sensitive data, just in case QCs eventually work.

[4] QC may never work. Although scaling up quantum computers is talked about as if it were an engineering issue, the people trying to do it are - in my opinion, and whether they realize it or not - trying to solve what physicists call the measurement problem. What constitutes a "measurement" in a quantum system - an action that causes the wave function describing a superposition of states to collapse into one state - is unknown. QCs work by causing the superposition created by the quantum algorithm to collapse into a state representing the answer, possibly solving a problem what would take a conventional computer years, or centuries, or ... Engineers working on QCs are trying to prevent a measurement - whatever that is - from occurring and the system decohering until they want it to. Defining what constitutes a quantum measurement is Nobel Prize territory, a problem that reaches into the very definition of reality in the transition from the realm of the very small to the realm we perceive. It is a problem that may never be solved, despite what investors are told.

I hope quantum computers do come to fruition. Not just for the practical reasons of solving some very difficult optimization problems and such, but because of the light it would shed on the measurement problem in physics. But I remain cautiously pessimistic.