Wednesday, April 27, 2016

Questioning quantum supremacy

KWRegan writes:
Gil Kalai is a popularizer of mathematics as well as a great researcher. His blog has some entries on Polymath projects going back to the start of this year. He has just contributed an article to the May AMS Notices titled, “The Quantum Computer Puzzle.” ...

Quantum supremacy has a stronger meaning than saying that nature is fundamentally quantum: it means that nature operates in concrete ways that cannot be emulated by non-quantum models. If factoring is not in BPP — let alone randomized classical quadratic time — then nature can do something that our classical complexity models need incomparably longer computations to achieve.

Kalai says:
Quantum computers are hypothetical devices, based on quantum physics, which would enable us to perform certain computations hundreds of orders of magnitude faster than digital computers. This feature is coined “quantum supremacy”, and one aspect or another of such quantum computational supremacy might be seen by experiments in the near future: by implementing quantum error-correction or by systems of noninteracting bosons or by exotic new phases of matter called anyons or by quantum annealing, or in various other ways. ...

A main reason for concern regarding the feasibility of quantum computers is that quantum systems are inherently noisy. We will describe an optimistic hypothesis regarding quantum noise that will allow quantum computing and a pessimistic hypothesis that won’t. ...

Are quantum computers feasible? Is quantum supremacy possible? My expectation is that the pessimistic hypothesis will prevail, leading to a negative answer.
I agree with Kalai that the quantum computer is the perpetual motion machine of the 21st century.


  1. I made a few comments on his blog and included your 35 second explanation but I have a little treat for you. The argument about Turing complexity from Feynman has a contradictory statement from Feynman himself about math relating to physics:

    "What goes on in no matter how tiny a region of space and no matter how tiny a region of time, according to the laws as we understand them today, takes a computing machine an infinite number of logical operations to figure out. Now, how could all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one stinky little bit of space-time is going to do?"
    — Richard Feynman

    He was clearly skeptical that we had the right explanation.

    1. That quote seemed to come from a lecture. I tracked it down:

      "It always bothers me that according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time [perturbative expansions with an infinite number of terms; path integrals over an infinite number of paths]. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypothesis that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed and the laws will turn out to be simple, like the checkerboard with all its apparent complexities. But this is just speculation." (The Character of Physical Law, 1964 Cornell Lectures)

  2. Quantum smauntum. The man who helped develop the damn thing knew there was something seriously wrong with it from the get go. How do we know this? Because the guy said so in one of his more lucid moments when he wasn't abusing bongo drums:

    "The shell game that we play to find n and j is technically called renormalization. But no matter how clever the word, it is what I would call a dippy process! Having to resort to such hocus-pocus has prevented us from proving the theory of quantum electrodynamics is mathematically self-consistent. .... I suspect that renormalization is not mathematically legitimate."


    Quantum Computing is literally nothing more than a slightly warmed over version of Douglas Adam's Infinite Improbability Drive. It basically works on the same level of required bullshit, and was also researched and funded by the government.

  3. Renormalization is less "dippy" than he suggests but speaking of sperm whales, Melville talked about one that was 90 feet long. However, no such giant has ever been recorded.

  4. When you turn an infinity into a finite number by integral butchery, you are only off by infinity. If you don't know what your numbers are attached to, it's hard to consider your answer correct.

    I am very much aware that younger people think renormalization is ok, but that's primarily because 1.)they were taught that it's ok, 2.) they didn't dare challange or question the dippy process for fear of ridicule in a climate of elitist snobbery, and 3.) They had to hurry on to the next piece of math to swallow and regurgitate on command for the next test. Academia is not the source of knowledge and understanding, it is the dispersion point for indoctrination and dogmatized information.

    If you really want to understand something, never ask someone who's job is utterly dependent upon a status quo of systemised mediocrity. If you really want to understand how something works, study it as it is coming apart.