Quantum Computers

[John Clark]

The difficulty in maintaining quantum coherence is the only reason we don't have practical quantum computers today, but Monday's issue of the journal Nature reported on a major advance in solving that problem. For the first time it has been proven that a quantum error correcting code called the "Bacon-Shor code" actually works in practice and not just in theory. They combined 9 physical Qubits that work correctly 98.9% of the time to make one virtual logic Qubit that works correctly 99.4% of the time, and that virtual logic Qubit would be the one you would use in an actual computation. Until now nobody has been able to prove that a logical Qubit can be made that is more reliable than any of the parts it is made out of.  This illustrates how different the quantum world is from the macro world we're accustomed to. If 9 people on an assembly line install a part into a machine and install the part correctly 98.9% of the time then the probability the entire finished machine will work correctly is only (0.989)^9 = 90.5% , but if the workers lived in the quantum world and they assemble the parts the way that Bacon-Shor tells them to then the finish machine will work correctly 99.4% of the time not 90.5%. The best thing is that although there are still engineering problems to solve there doesn't seem to be any fundamental reason Bacon-Shor can't be scaled up.

Kenneth Brown, what are the authors of the paper, says:

"What's amazing about fault tolerance is it's a recipe for how to take small unreliable parts and turn them into a very reliable device. And fault-tolerant quantum error correction will enable us to make very reliable quantum computers from faulty quantum parts. The key part of quantum error correction is redundancy, which is why we needed 9 qubits in order to get one logical qubit. That redundancy helps us look for errors and correct them, because an error on a single qubit can be protected by the other eight."

Laird Egan, another author of the paper says:

"This is really a demonstration of quantum error correction improving performance of the underlying components for the first time. It's really a proof of concept that quantum error correction works. It shows that we can get all the pieces together and do all the steps. And there's no reason that other platforms can't do the same thing as they scale up."

Fault-tolerant control of an error-corrected qubit

John K Clark    See what's on my new list at  Extropolis

[Brent Meeker]

On 10/6/2021 4:58 AM, John Clark wrote:

The difficulty in maintaining quantum coherence is the only reason we don't have practical quantum computers today,

Well  there is also the fact that there are only about two dozen problems for which there is a known quantum algorithm faster than the best classical algorithm...and even there "faster" means in the limit of large problem size, not necessarily in realistic problem sizes.  And of those two dozen problems all but a handful are contrived specifically to show that there exist problems for which a QC is necessarily faster (in the large problem limit).

And when you talk about practical computers, how much more would it be worth to you if the word processor on your laptop was a thousand times faster or your computer game refreshed ten times faster.  The "practical" applications were initially supposed to be in encryption, both breaking and making unbreakable.  But now all the financial institutions are switching from RSA to encryption for which there's no QC algorithm to break it.

Brent

[spudb...@aol.com]

Yet advances in the prowess of digital computing leaps ahead.  Making me wonder if quantum computing has become the nuclear fusion of the computing world? 

The Convergence of the Digital With the Physical and the Biological

https://www.infotoday.com/OnlineSearcher/Articles/Technology-and-Power/The-Convergence-of-the-Digital-With-the-Physical-and-the-Biological-148822.shtml

"If recent advances in digital technologies are truly taking us beyond the digital revolution, that is a sufficient reason for libraries to take heed of the Fourth Industrial Revolution. What does it exactly mean that the lines between the physical, the digital, and the biological spheres are getting blurred? How will that relate to the future of libraries? What kind of libraries would be appropriate for the world in which the digital blur and mix into the physical and the biological and vice versa?"

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[John Clark]

On Wed, Oct 6, 2021 at 6:10 PM 'Brent Meeker' via Everything List <everyth...@googlegroups.com> wrote:

> here are only about two dozen problems for which there is a known quantum algorithm faster than the best classical algorithm

True, but considering the fact that we don't have a working quantum computer that programmers can use to try out ideas and tweak things it's a wonder we have any quantum algorithms at all. Imagine trying to write a large complex computer program in hexadecimal with just pencil and paper and no computer; it might not be exactly impossible but it would sure be hard as hell, and I doubt it would run perfectly the first time it was actually tried out on a real computer.

> ...and even there "faster" means in the limit of large problem size, not necessarily in realistic problem sizes. 

All the applications in which quantum computers are substantially superior to conventional computers are problems in which a very small increase in problem size results in a gargantuan increase in the number of computations required for a solution; and such problems turn out to be the norm not the exception in our real physical world. Nearly a century ago Niels Bohr was able to calculate from first principles the spectrum of the simplest element hydrogen, but because the calculations became too complex he couldn't do it for the second simplest element helium, and even today we can't do much better. From first principles no conventional computer can calculate, even approximately, what a large organic molecule will do, but a quantum computer could.    

 

> And when you talk about practical computers, how much more would it be worth to you if the word processor on your laptop was a thousand times faster

Word processing on a quantum computer is like killing a fly with a sledgehammer, nobody is suggesting that.  A 100 Qubit quantum computer could make far more computations than all the conventional computers on Earth combined, but only if those 100 Qubits were nearly perfect; that's why quantum error correction is so important; it might take over a 1000 imperfect physical Qubits, or maybe only a few dozen, to make one nearly perfect logical Qubit that can be used in computations that will change the world forever. I have little doubt that when working quantum computers become available, quantum error correction schemes will be developed that are superior to anything we have now.

> The "practical" applications were initially supposed to be in encryption, both breaking and making unbreakable. 

I always thought cryptology was just a trivial application of quantum computers and that the real killer application was the simulation of quantum systems.  

 

> But now all the financial institutions are switching from RSA to encryption for which there's no QC algorithm to break it.

I assume you're talking about lattice-based cryptography, and it's true there is currently no QC algorithm to break it, but I wouldn't be too confident that situation will never change once quantum computers become available and cryptographers really try to break it. And nobody has devised a lattice-based system that is practical, the key it uses is HUGE and it's s-l-o-w,  it would take so long to use a credit card to buy something on Amazon that people would lose patience, the company would go out of business, and brick and mortar stores would come back in style as would paper money.

John K Clark    See what's on my new list at  Extropolis

nqx

 

[spudb...@aol.com]

My contention is that computing is not wholly reliant on only quantum computing. 

Purdue researchers create ‘self-aware’ algorithm to ward off hacking attempts

https://www.purdue.edu/newsroom/releases/2021/Q4/purdue-researchers-create-self-aware-algorithm-to-ward-off-hacking-attempts.html

A hybrid computing future is most likely.

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.

[Lawrence Crowell]

The quantum Hamming distance is hard to reliably measure. It tends to ignore the quantum complexity of the quantum phase. The inner space is a hyperbolic space that is a type of moduli of curves or paths. This approach may in the long run be preferable.

LC

[John Clark]

Perhaps this explains what has occurred better than I have:

Scientists are one step closer to error-correcting quantum computers