Monday, November 7, 2022

Quantum Computing Skeptic gives Lecture

Gil Kalai gave a lecture on the impossibility of quantum computers, summarized here:
My argument for the impossibility of quantum computers lies within the scope of quantum mechanics and does not deviate from its principles. In essence, the argument is based on computational complexity and its interpretation, and it is discussed in-depth in my papers which also include a discussion of general conclusions that derive from my argument and relate to quantum physics, alongside suggestions of general laws of nature that express the impossibility of quantum computation.

My argument mostly deals with understanding quantum computers on the intermediate scale (known as NISQ computers, an abbreviation of Noisy Intermediate Scale Quantum), that is, quantum computers of up to at most several hundreds of qubits. It is expected that on this scale we will be able to construct quantum codes of a quality sufficient for the construction of bigger quantum computers. It is further expected that on this scale the quantum computer will achieve computations far beyond the ability of powerful classical computers, that is, will achieve quantum computational supremacy. The Google’s Sycamore computer is an example of a noisy intermediate-scale quantum computer.

As specified later, it is my argument that NISQ computers cannot be controlled. Hence:

  1. Such systems cannot demonstrate significant quantum computational advantage.
  2. Such systems cannot be used for the creation of quantum error-correcting codes.
  3. Such systems lead to non-stationary and even chaotic distributions.

Note that he does not say that quantum mechanics is wrong. He denies that quantum computing is a necessary consequence.

A lot of smart people and a lot of research funding say that he is wrong.

Maybe I am just a contrarian, but it seems to me that they should have been able to prove him wrong by now. They have not.


  1. Hi Roger. I had an insight on P v. NP and filed for a doctorate because I felt the insight implied my result. They tossed me one. I classified it under Quantum Theory. Not sure if you were involved in review, but in any case thanks for some early inspiration. Jon

  2. Dear Roger,

    It's good to see the creator of 'Gina says' getting honoured.


  3. I agree with Gil wholeheartedly, but his argument does suggest a needed completion to QM, otherwise there would be no argument. As I was saying with Bell's inequality, people have neglected background fields violating measurement independence:

    Contrary to your Einstein trashing, it's the path integral and QM cranks who are misleading everyone with bogus metaphysics. A more complete theory might demystify entanglement and superposition and possibly reveal the "analog" nature to the computation. The measurement problem is obscuring things.

    E-T bounds and Boltzmann's law easily put pessimistic bounds on the SPEED of quantum evolution. QCs can experience INTERNAL decoherence, not just external decoherence. There is no global phase, initial conditions are sensitive, and QEC can actually destroy a continuous process. Good luck with that.