Cold Fusion was first accomplished by Chadwick in 1932 when beryllium was fused with helium to produce carbon. Since then, no practical progress has been made. Similarly, quantum calculations have been demonstrated to divide fifteen by five. Eighty years from now, it is predicted that no practical progress will be made to factor 87612876487643876468432876587556950288716267617831 into its two prime constituents using quantum computer hardware. That is because of noise and uncertainty.
Even more difficult than factoring a composite number into its prime coefficients, is the task of decrypting AES 256 without the key. The cipher feedback and the initialization vectors are powerful complications for any imaginary quantum computer to unravel. It is easy to encrypt a file and then encrypt that file and then repeat that scheme until it is practically unbreakable.
Quantum cryptanalysis is as intractable as cold fusion for reasons that are shared between the two technological goals. Facts of atomic and nuclear levels of modeling do not encompass all realities. Beryllium has a nucleus with four protons and even numbered elements are the most common due to the fact that helium has two protons. Beryllium is rare in spite of that. Quantum computers are wished to be modeled as easily as the Bohr hydrogen model, but even a sugar molecule is beyond the ken.