In my book â€“ and in my courses â€“ I also pay attention to quantum computers. This is partly because it is a subject that regularly appears in the news and is therefore in the spotlight, but also because the reports on it invariably tell us that quantum computers use the â€“ according to the authors absurd â€“ properties of the quantum world. Which means that the QuBits of the quantum computer can have two values â€“ 0 and 1 â€“ at the same time. Absurd indeed, if that’s true.

## A wrong material image

I think that idea is wrong. The QuBits are not material before the measurement. They are only a non-material probability distribution of two values, 0 and 1. That is what you have to assume according to quantum mechanics and which works very well as far as quantum mechanical prediction is concerned. During the measurement, the probability distribution changes abruptly into a material manifestation, ie a 0 or a 1. If you have entangled a number of QuBits that you then subject to some digital manipulations, those manipulations will have been performed on all possible states of those entangled QuBits. For example, if you have entangled 10 QuBits â€“ which can therefore contain 2^{10} = 1024 possible different states â€“ then those QuBits will actually perform 1024 different calculations simultaneously in one single calculation step. However, the outcomes are not yet materialized, they are ephemerally locked in the quantum probability distribution that is not material. A measurement will materialize just one of those 1024 possible states. It is therefore important to set up the QuBits and their entanglement in such a way that you get the outcome that is interesting for your purposes. That is not easy, of course, especially since QuBits are ‘unstable’, which means that they decay within a very short time – usually expressed in nanoseconds – into a 0 or a 1 with their entanglement broken.

## What is it that triggers the quantum collapse?

How the measurement brings about the material manifestation of the QuBits is still an unsatisfactory answered question. The scientists who work on quantum computers do still adhere to the decoherence hypothesis, so that they cool their QuBits to absolute zero and mount them as vibration-free as possible. In my book I argue that the decoherence hypothesis is logically untenable. That would mean that the scientists’ chosen approach to contructing quantum computers has little chance of real success, despite their great financial resources.

## The role of the observer

Many quantum physicists are gradually admitting â€“ albeit not wholeheartedly â€“ that the observer in the measurement plays an indispensable role in the materialization of the quantum object â€“ and therefore also of the entangled QuBits. Carlo Rovelli explains this by assuming that all objects in the universe only exist in relation to each other. That way, he doesn’t have to assign a special role to the human observer, though. Everything is an observer.

## Interesting articles about quantum computers

Nevertheless, the subject is extremely interesting and I am therefore closely following progress in this area. The internet links to articles that I think are worth your attention are presented below and are regularly updated.

- October 2021 â€“ Delft Integraal: Delft Spinoza Prize winner has remarkable plans.
- September 2021 â€“ Quanta Magazine: Major Quantum Computing Strategy Suffers Serious Setbacks.
- January 2019 – HPC Wire: The Case Against â€˜The Case Against Quantum Computingâ€™.
- November 2018 – IEEE Spectrum: The Case Against Quantum Computing.
- February 2018 â€“ Quanta magazine: The Argument Against Quantum Computers.
- February 2007 – WIRED: David Deutch, the father of quantum computing.