(March 18, 2022 at 11:27 am)Jehanne Wrote: Another issue is error detection and correction. As a physicist, do you think that one is even solvable? Factoring large integers is something that can be checked, of course, but other types of simulations presuppose numerical accuracy and stability. If such is not possible with quantum computers, their use would seem rather limited.
There are ways to do error correction, but the most important thing is to prevent errors in the first place. In theory, one can do noise reduction schemes on the quantum system that work mathematically. I just don't think the math corresponds to reality.
The computation power of a quantum computer is exponential to the number of qubits. The problem is that the probability of error due to noise also goes up exponentially. Otherwise, we would have magic.
I forget the theoretical techniques for noise reduction and error correction, but I do know they rely on a decorrelated noise model. The problem is that perturbations within a quantum system have a time evolution, and I am convinced that the noise is not decorrelated during that time. If you want 100 cubit systems to give meaningful results, you will have to wait exponentially longer times for the system to achieve a noise-free state (and then, there is the problem of thermodynamics, where it will get hit by a stray bit of energy from somewhere).
Quantum Computing has been very disappointing, and I have been convinced for 30 years that it will not amount to much, except in the areas of simulating quantum systems. Because it is a quantum system, it can simulate quantum systems.
