Quantum computing infeasibility due to quantum tomography?

Post a reply


This question is a means of preventing automated form submissions by spambots.

BBCode is ON
[img] is ON
[flash] is OFF
[url] is ON
Smilies are OFF
Topic review
   

Expand view Topic review: Quantum computing infeasibility due to quantum tomography?

Re: Quantum computing infeasibility due to quantum tomograph

Post by gill1109 » Sat Sep 07, 2019 12:17 am

This article tells exactly why the quantum computing dream is going to become a nightmare. I have copy-pasted the text of the article on Phys.org https://phys.org/news/2019-09-quantum.html Emphasis on three phrases in the beginning of the article is mine. I have the feeling that these statements were "tongue in cheek" remarks. Indeed, Johansson and Larsson have shown how some famous quantum algorithms actually work, and they have shown that they do not always work as spectacularly as many famous publications suggest. In fact, they show that there is no point in building quantum computers for the sake of implementing some particular algorithms at all! Obviously, it would be politically incorrect to say this out loud.

Scientists at Linköping University have shown how a quantum computer really works and have managed to simulate quantum computer properties in a classical computer. "Our results should be highly significant in determining how to build quantum computers," says Professor Jan-Åke Larsson.

The dream of superfast and powerful quantum computers has again been brought into focus, and large resources have been invested in research in Sweden, Europe and the world. A Swedish quantum computer is to be built within ten years, and the EU has designated quantum technology one of its flagship projects. At the moment, few useful algorithms are available for quantum computers, but it is expected that the technology will be hugely significant in simulations of biological, chemical and physical systems that are far too complicated for even the most powerful computers currently available. A bit in a computer can take only the value one or zero, but a quantum bit can take all values in between. Simply put, this means that quantum computers do not need to take as many operations for each calculation they carry out.

Two degrees of freedom

Professor Jan-Åke Larsson and his doctoral student Niklas Johansson, in the Division for Information Coding at the Department of Electrical Engineering, Linköping University, have come to grips with what happens in a quantum computer and why it is more powerful than a classical computer. Their results have been published in the scientific journal Entropy.

"We have shown that the major difference is that quantum computers have two degrees of freedom for each bit. By simulating an additional degree of freedom in a classical computer, we can run some of the algorithms at the same speed as they would achieve in a quantum computer," says Jan-Åke Larsson.

They have constructed a simulation tool, Quantum Simulation Logic, QSL, that enables them to simulate the operation of a quantum computer in a classical computer. The simulation tool contains one, and only one, property that a quantum computer has that a classical computer does not: one extra degree of freedom for each bit that is part of the calculation.

"Thus, each bit has two degrees of freedom: it can be compared with a mechanical system in which each part has two degrees of freedom—position and speed. In this case, we deal with computation bits—which carry information about the result of the function, and phase bits—which carry information about the structure of the function," Jan-Åke Larsson explains.

Quantum algorithms

They have used the simulation tool to study some of the quantum algorithms that manage the structure of the function. Several of the algorithms run as fast in the simulation as they would in a quantum computer.

"The result shows that the higher speed in quantum computers comes from their ability to store, process and retrieve information in one additional information-carrying degree of freedom. This enables us to better understand how quantum computers work. Also, this knowledge should make it easier to build quantum computers, since we know which property is most important for the quantum computer to work as expected," says Jan-Åke Larsson.

Jan-Åke Larsson and his co-workers have also supplemented their theoretical simulations with a physical version built with electronic components. The gates are similar to those used in quantum computers, and the toolkit simulates how a quantum computer works. With its help students, for example, can simulate and understand how quantum cryptography and quantum teleportation works, and also some of the most common quantum computing algorithms, such as Shor's algorithm for factorization. (The algorithm works in the current version of the simulation but is equally fast—or slow—as in classical computers).

Re: Quantum computing infeasibility due to quantum tomograph

Post by minkwe » Mon Sep 02, 2019 9:21 am

Some people only learn the hard way.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Sun Sep 01, 2019 6:49 pm

Joy Christian wrote:***
The Argument Against Quantum Computers: https://indico.cern.ch/event/839574/

PDF of the talk: https://indico.cern.ch/event/839574/att ... 7/CERN.pdf


Image

If so, then how many trillions will have been wasted? How many careers will have been ruined for raising a skeptical voice? And how many mediocre academics will have their careers made?

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Sun Sep 01, 2019 11:42 am

***
The Argument Against Quantum Computers: https://indico.cern.ch/event/839574/

PDF of the talk: https://indico.cern.ch/event/839574/att ... 7/CERN.pdf

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by FrediFizzx » Sat Aug 03, 2019 7:41 am

OK guys, let's get back on-topic for this thread.
.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Sat Aug 03, 2019 4:00 am

Heinera wrote:Scott Aaronson is heading the Quantum Complexity group at University of Texas at Austin. Not exactly a demotion. Plus they also tenured his wife. He has written about his transition on his blog.

Yeah, right. Unlike you, I know the inside story. Ask the Provost of MIT, and ask the President of the University of Texas at Austin. So if I were you, I would keep your anonymous opinions out of this. In any case, nothing justifies Aaronson's obnoxious online behavior, as John Duffield noted earlier in this thread:

JohnDuffield wrote:
How on Earth are academics like Scott Aaronson allowed to spray such obnoxious bile and remain in post?


If Aaronson were wiser, then he would have remained anonymous like you. That way what you say and do has no adverse consequences for you.

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by Heinera » Sat Aug 03, 2019 3:32 am

Scott Aaronson is heading the Quantum Complexity group at University of Texas at Austin. Not exactly a demotion. Plus they also tenured his wife. He has written about his transition on his blog.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Sat Aug 03, 2019 12:15 am

gill1109 wrote:
...my usually very wise friend Scott Aaronson ...

Elsewhere I have explained just how "wise" Scott Aaronson is:
Joy Christian wrote:
Joy Christian wrote:
I have written up a long-overdue refutation of Scott Aaronson's online critique of my local-realistic model:

Refutation of Scott Aaronson's Critique of my Disproof of Bell's Theorem

Image

Fortunately, the Truth cannot be starved off so easily, and Aaronson has not succeeded in his goal. :)

I hear that Aaronson is no longer at MIT. Could my online treatment by him have anything to do with his departure from MIT? Unfortunately, some other guilties have retired from their academic positions and thereby escaped any repercussions for their online and offline behavior.

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by gill1109 » Fri Aug 02, 2019 10:10 pm

minkwe wrote:Oops!

Take a look at
https://www.phasespacecomputing.com/
Image

You will also love https://arxiv.org/abs/1905.05082 Quantum Simulation Logic, Oracles, and the Quantum Advantage, Niklas Johansson, Jan-Åke Larsson
Abstract: Query complexity is a common tool for comparing quantum and classical computation, and it has produced many examples of how quantum algorithms differ from classical ones. Here we investigate in detail the role that oracles play for the advantage of quantum algorithms. We do so by using a simulation framework, Quantum Simulation Logic (QSL), to construct oracles and algorithms that solve some problems with the same success probability and number of queries as the quantum algorithms. The framework can be simulated using only classical resources at a constant overhead as compared to the quantum resources used in quantum computation. Our results clarify the assumptions made and the conditions needed when using quantum oracles. Using the same assumptions on oracles within the simulation framework we show that for some specific algorithms, like the Deutsch-Jozsa and Simon's algorithms, there simply is no advantage in terms of query complexity. This does not detract from the fact that quantum query complexity provides examples of how a quantum computer can be expected to behave, which in turn has proved useful for finding new quantum algorithms outside of the oracle paradigm, where the most prominent example is Shor's algorithm for integer factorization.

See also:

https://link.springer.com/content/pdf/10.1007%2Fs11128-017-1679-7.pdf
Efficient classical simulation of the Deutsch–Jozsa
and Simon’s algorithms
Niklas Johansson, Jan-Åke Larsson

https://www.researchgate.net/project/Efficient-Classical-Simulation-of-Quantum-Algorithms

Unfortunately, my usually very wise friend Scott Aaronson has not understood what Larsson and Johansson are doing. Somehow it is very hard to explain, that is true...
https://www.scottaaronson.com/blog/?p=3638#comment-1752690
https://www.scottaaronson.com/blog/?p=3638#comment-1753676

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Thu Aug 01, 2019 1:57 pm

***
Exponential speed up done classically: https://www.mdpi.com/2076-3417/9/15/3029/htm.

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Thu Apr 25, 2019 2:26 am

***
Quantum Hype and Quantum Skepticism: https://cacm.acm.org/magazines/2019/5/2 ... mbV30JZ5k0

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Mon Mar 18, 2019 2:07 am

Joy Christian wrote:
JohnDuffield wrote:
How on Earth are academics like Scott Aaronson allowed to spray such obnoxious bile and remain in post?

The fault lies entirely with the physics community as a whole, especially with those holding professorial positions and positions of power. There is no accountability for abusive actions like those of Scott Aaronson and others. I wrote to the Provost of MIT when Aaronson was at MIT, but his office did nothing. Their reply to me was that what Aaronson does on his private blog does not amount to either scientific or professional misconduct. The administrators of FQXi, Max Tegmark and Anthony Aguirre, also sided with Aaronson and seemed to be grateful to him for his actions, which led to my resignation from FQXi. Even people like Harvey Brown and Samson Abramsky of my own college at Oxford University, Wolfson College, sided with Aaronson and acted against me, thereby condoning his abusive actions. The reason behind this is nothing but academic politics. Sadly, I have witnessed its dark underbelly from inside for many years.

"... privilege often breeds a dangerous mixture of ineptitude and arrogance, as well as incubating the kind of unhinged ideas that could appeal only to people removed from ordinary life, who tend to see the world in terms of crass abstractions." This opinion appears in the piece written today by John Harris in the context of Brexit for The Guardian, but it applies equally to the proponents of the so-called "quantum computing."

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by JohnDuffield » Wed Mar 06, 2019 11:32 am

Joy Christian wrote:The fault lies entirely with the physics community as a whole, especially with those holding professorial positions and positions of power. There is no accountability for abusive actions like those of Scott Aaronson and others. I wrote to the Provost of MIT when Aaronson was at MIT, but his office did nothing. Their reply to me was that what Aaronson does on his private blog does not amount to either scientific or professional misconduct. The administrators of FQXi, Max Tegmark and Anthony Aguirre, also sided with Aaronson and seemed to be grateful to him for his actions, which led to my resignation from FQXi. Even people like Harvey Brown and Samson Abramsky of my own college at Oxford University, Wolfson College, sided with Aaronson and acted against me, thereby condoning his abusive actions. The reason behind this is nothing but academic politics. Sadly, I have witnessed its dark underbelly from inside for many years.
This is not good. Unfortunately it appears to be endemic, albeit without quite so much bile. I've had people tell me they've been told "don't rock the boat or you'll never make full professor". I hear stories about people struggling to get a paper on the arXiv, or into a high-impact journal. So I'm afraid I also have my doubts about peer review, as per this cartoon by Nick Kim:

Image

Not only that, but it spills out into life at large. For example Q-reeus has employed the "crank" ad-hominem, and is now using the old "you have been debunked" trick. Sigh. I will start a thread, but he won't point out any flaws.

Anyway, apologies for the digression. What are you working on at the moment? Perhaps I could start a thread about something relevant.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Joy Christian » Wed Mar 06, 2019 7:59 am

JohnDuffield wrote:
How on Earth are academics like Scott Aaronson allowed to spray such obnoxious bile and remain in post?

The fault lies entirely with the physics community as a whole, especially with those holding professorial positions and positions of power. There is no accountability for abusive actions like those of Scott Aaronson and others. I wrote to the Provost of MIT when Aaronson was at MIT, but his office did nothing. Their reply to me was that what Aaronson does on his private blog does not amount to either scientific or professional misconduct. The administrators of FQXi, Max Tegmark and Anthony Aguirre, also sided with Aaronson and seemed to be grateful to him for his actions, which led to my resignation from FQXi. Even people like Harvey Brown and Samson Abramsky of my own college at Oxford University, Wolfson College, sided with Aaronson and acted against me, thereby condoning his abusive actions. The reason behind this is nothing but academic politics. Sadly, I have witnessed its dark underbelly from inside for many years.

***

Re: Quantum computing infeasibility due to quantum tomograph

Post by Q-reeus » Wed Mar 06, 2019 3:49 am

JohnDuffield wrote:You're sounding like Scott Aaaronson. You have nothing to do with me being here. I emailed Joy about his 2007 article Quantum Entanglement: is Spookiness under threat, and we got talking. The moot point is that when you know about electron spin, you know that Joy was right. And yet he received dreadful abuse for his pains. This was an injustice. How on Earth are academics like Scott Aaronson allowed to spray such obnoxious bile and remain in post?

As for how gravity works, you can't point out where it's wrong. If you think you can, please start a thread and do so. But please do so on another thread, and respect the OP. Ditto if you want to talk about neutrino spin.

Right, well relieved to know I wasn't responsible for you being here. As for your put-up-or-shut-up dare, no. Feel free to start a thread on either topic, and I will likely chip in to point out obvious flaws you were alerted to numwerouss times in the past, but to no good effect. Your choice John.

Re: Quantum computing infeasibility due to quantum tomograph

Post by JohnDuffield » Wed Mar 06, 2019 1:45 am

You're sounding like Scott Aaaronson. You have nothing to do with me being here. I emailed Joy about his 2007 article Quantum Entanglement: is Spookiness under threat, and we got talking. The moot point is that when you know about electron spin, you know that Joy was right. And yet he received dreadful abuse for his pains. This was an injustice. How on Earth are academics like Scott Aaronson allowed to spray such obnoxious bile and remain in post?

As for how gravity works, you can't point out where it's wrong. If you think you can, please start a thread and do so. But please do so on another thread, and respect the OP. Ditto if you want to talk about neutrino spin.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Q-reeus » Tue Mar 05, 2019 7:39 pm

JohnDuffield wrote:
Q-reeus wrote:Joy you really should have done some basic checking before posting that link. John Duffield aka 'Physics Detective' is a crank especially well known for his 'visual' interpretation of GR.
When I talk about GR, I refer to what Einstein said. Things like this from 1920:

“Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable”.

That's because I've read the history. I've read the history of quantum mechanics too. And papers such as Hans Ohanian’s what is spin?. When you understand these things, you understand why quantum computing hasn't achieved anything in nearly forty years.

Oh dear. Guess I should take at least partial responsibility for JD signing up here. Partial because I suspect someone else here alerted John to my earlier entry above.
Rather than disputing again some of your erroneous ideas that were repeatedly dealt with over at another forum, I will refer any interested reader to check out these:
http://physicsdetective.com/how-gravity-works/
http://physicsdetective.com/the-screw-n ... magnetism/
Don't have the time or interest to comb through each and every article there - just selected two whose main themes were persistently promoted over at another forum.
Hopefully the conceptual errors in both articles are clearly evident. If not, too bad - JD may end up with one or more new disciples.
[PS - I myself was rather partial to Ohanian's spin model for an electron - one which was improved on btw by a later article by Andre Gsponer, - What Is Spin http://arxiv.org/abs/physics/0308027
Unfortunately, I cannot see how it could successfully be adapted to explain the experimentally observed spin half for neutrinos!]

Re: Quantum computing infeasibility due to quantum tomograph

Post by JohnDuffield » Tue Mar 05, 2019 12:52 pm

Q-reeus wrote:Joy you really should have done some basic checking before posting that link. John Duffield aka 'Physics Detective' is a crank especially well known for his 'visual' interpretation of GR.
When I talk about GR, I refer to what Einstein said. Things like this from 1920:

“Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable”.

That's because I've read the history. I've read the history of quantum mechanics too. And papers such as Hans Ohanian’s what is spin?. When you understand these things, you understand why quantum computing hasn't achieved anything in nearly forty years.

Re: Quantum computing infeasibility due to quantum tomograph

Post by Q-reeus » Mon Mar 04, 2019 8:53 pm

Joy Christian wrote:***
Q-reeus, I don't agree with everything John Duffield is saying, but he is entitled to his views. And I agree with his view that quantum computing is "pie in the sky and jam tomorrow." :)

***

Make that a threesome Joy. However whether it's down to mere infeasibility e.g. environmental decoherence, ineffectualness of 'error correction' etc., or fundamental physics i.e. existence or non-existence of entanglement and/or quantum superposition, is where it's really at. Most if not all of the QC critics you quoted and linked to earlier here (and in other threads), fall under the former category best I can tell. 8-)

Top

cron
CodeCogs - An Open Source Scientific Library