# Is quantum supremacy a thing?



## KenOC (Mar 7, 2011)

Interesting news today. "Researchers in UC Santa Barbara/Google scientist John Martinis' group have made good on their claim to *quantum supremacy*. Using 53 entangled quantum bits ('qubits'), their Sycamore computer has taken on -- and solved -- a problem considered intractable for classical computers.

" 'A computation that would take 10,000 years on a classical supercomputer took 200 seconds on our quantum computer,' said Brooks Foxen, a graduate student researcher in the Martinis Group. The feat is outlined in a paper in the journal _Nature_."

Any idea on what this means, if true? How will this change things?


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## Totenfeier (Mar 11, 2016)

Others more learned in computing than I may beg to differ, but IMHO, we will, as per usual, learn too much too quickly, without an equivalent jump in wisdom and foresight to guide us toward a proper use of what we learn, all with billions of times greater efficiency. "Just because you can, doesn't mean you should (or _must)._" What was it that goeth before a fall? Hmm...


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## Guest (Oct 24, 2019)

KenOC said:


> Interesting news today. "Researchers in UC Santa Barbara/Google scientist John Martinis' group have made good on their claim to *quantum supremacy*. Using 53 entangled quantum bits ('qubits'), their Sycamore computer has taken on -- and solved -- a problem considered intractable for classical computers.
> 
> " 'A computation that would take 10,000 years on a classical supercomputer took 200 seconds on our quantum computer,' said Brooks Foxen, a graduate student researcher in the Martinis Group. The feat is outlined in a paper in the journal _Nature_."
> 
> Any idea on what this means, if true? How will this change things?


I tried reading, but even the summary requires a Rosetta Stone for me to decipher. It sounds cool. But I couldn't tell you what the implications are.


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## Strange Magic (Sep 14, 2015)

According to this BBC article, "classical" (I like that!) computing is not yet down and out:

https://www.bbc.com/news/science-environment-50154993


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## Room2201974 (Jan 23, 2018)

Strange Magic said:


> According to this BBC article, "classical" (I like that!) computing is not yet down and out:
> 
> https://www.bbc.com/news/science-environment-50154993


I'm holding out for "impressionistic computing" whereby the computer only suggests vague ideas about what the answer might be. Sounds more fun to me!


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## Strange Magic (Sep 14, 2015)

Room2201974 said:


> I'm holding out for "impressionistic computing" whereby the computer only suggests vague ideas about what the answer might be. Sounds more fun to me!


I agree; we should encourage computers to be creative, to have a sense of play, to free-associate.


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## Manxfeeder (Oct 19, 2010)

Well, we have the computer. Now it's time for someone to publish a hitchhiker's guide to the galaxy.


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## Totenfeier (Mar 11, 2016)

Manxfeeder said:


> Well, we have the computer. Now it's time for someone to publish a hitchhiker's guide to the galaxy.


...............42.


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## Guest (Oct 24, 2019)

KenOC said:


> Interesting news today. "Researchers in UC Santa Barbara/Google scientist John Martinis' group have made good on their claim to *quantum supremacy*. Using 53 entangled quantum bits ('qubits'), their Sycamore computer has taken on -- and solved -- a problem considered intractable for classical computers.
> 
> " 'A computation that would take 10,000 years on a classical supercomputer took 200 seconds on our quantum computer,' said Brooks Foxen, a graduate student researcher in the Martinis Group. The feat is outlined in a paper in the journal _Nature_."
> 
> Any idea on what this means, if true? How will this change things?


I read the linked article, a peculiar combination of specific and vague.

Think of it this way, you have a qubit, which may be an atom in a trap which is either spin up or spin down. You initialize the qubit spin down. Then you hit the qubit with some pulses of radiation. A full pulse would flip it from down to up, but you only give half a pulse. In quantum world there is no such thing as half way up. so now you have a qubit which is in a superposition of up and down. If you measure it you have a 50% chance of reading up, 50% chance down, but it is some mysterious sense in both states at once. Now you have an array of these qubits in these superpositions of states and you let them "interact." Think of it like two pendulums mounted on the same support, they can push on each other a bit and maybe transfer energy from one pendulum to the other. The superposition state of a qubit is modified by interacting with a neighboring qubit. You turn off the interaction and you have qubits which are not only in superposition states, but are _entangled_ with other qubits. Two qubits may have indeterminate states, but if you measure one qubit that constrains what you might get if you measure a second qubit, they are correlated. Finally you read out the state of the qubit array over and over and get a statistical determination of the final state, that is the "calculation." It is "quantum supremacy" because if you tried to calculate what the answer would be using a classical computer the number of possible states of the system that you would have to consider is so large as to make the calculation intractable.

Technically impressive that they can get all of those qubits working together. The problem is that any noise from the environment getting into the system would spoil the quantum states and ruin the calculation.

But the skeptic in me asks, is that a _calculation_? You've just make a very clean quantum system evolve for a while and shown that it is practically impossible to calculate the behavior of that system using a conventional computer. But the physical evolution of the system is a _calculation_? If I let some water flow down a pipe I can create a turbulent fluid flow that might require thousands of years for a computer to model accurately. It that fluid flow a _calculation_. A segment of RNA folds into a pseudoknot in a microsecond. A computer calculation of that folding pathway might take 100 years. The the RNA model do a _calculation_ by folding?

The bottom line is they may be able to formulate some very narrowly defined mathematical problems in terms that can be addressed by the quantum computer (they are always mentioning cryptography). Maybe some of those problems are game changers. But I don't see that there is a path to a general purpose quantum computer.

The comparison to the hitchhiker's guide is apt, the calculation is an answer in search of a question.


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## Guest (Oct 24, 2019)

I follow the Twitter feed for Nature, and saw this story mentioned there. It takes about the breakthrough but that it is also very limited in what it can do. Highly powerful but also highly specific. In the near term, classical computers are in no danger of becoming obsolete.


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## Room2201974 (Jan 23, 2018)

Totenfeier said:


> ...............42.


Crosby did him one better!


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