# Have you heard of Quantum Computing?



## neilms (Oct 1, 2013)

I was just looking at an interesting documentary called "Defeating the hackers". They discussed a new type of computer called a quantum computer that has proven to be theoretically capable of breaking any of the encryption systems used today on the Internet - *immediately*. The computer tests all possibilities in parallel rather than in sequence. I am still trying to fathom it!

Nothing was said about the operating system it uses, but it is still a prototype machine with massive hardware like the 1950's style computers.

This is the first time I heard of such an incredible machine. I was wondering if anyone else here had seen the documentary as well?


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## funky (Oct 1, 2013)

Hi,

I did not see the documentary, however, I know a little bit about quantum computing. The good news is, that a quantum computer is not capable of breaking all encryption systems. However, the bad news is that it can break all currently used asymmetric encryption systems. Asymmetric cryptography today is mainly based on the factoring problem or the discrete logarithm problem. Both these problems can be efficiently computed on a quantum computer due to Shor's algorithm.

For attacking a symmetric cipher with a quantum computer there is Grover's algorithm, but this algorithms only speeds up the computation by the square root, for example: if you have data encrypted with AES-256 (using a random 256 bit key), on a quantum computer this will be only as hard as breaking AES-128 on a regular computer.

So, for being safe with a symmetric cipher in the quantum age just double the keysize. For asymmetric cryptography there might also be hope: it is known that if P != NP, that even a quantum computer can't solve NP-complete problems efficiently. These problems can be used to construct an asymmetric encryption system.


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## fonz (Oct 3, 2013)

Not many people appear to be aware of quantum computing. And even scientists sometimes dismiss it as theoretical tomfoolery that will never actually happen. Quantum computing is IMO very interesting, not only because of the computational power it potentially yields, but also because it applies sexy aspects of physics to computing. Theory and practice are two different things, though. Because of the physics involved, building an actual quantum computer is technologically very challenging (quantum computers consisting of some few-bit gates do exist but are the size of a big-ass lecture hall, not unlike the earliest traditional computers) and that is exactly why people are skeptical about whether a useful full-scale quantum computer will ever get built. Personally I think it will happen, but probably not in my lifetime.


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## break19 (Oct 4, 2013)

Don't be so pessimistic.  After all, it only took a few decades to go from 1950 style massive building housing a single computer, to the 1980s computer explosion.

Now, it might take another 20-30 years for the new qubit based systems to miniaturize the same way.  I don't know about you, but I do plan to still be around in 20-30 years.

After all, that's about the time my (now 6 years old) daughter will hopefully be giving me grandkids! *smile*


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## break19 (Oct 4, 2013)

Oh, and from what I've read on the subject, the computer that is currently in operation, is very powerful, but there is a huge debate on whether or not it is an actual quantum computer.

It's most definitely more powerful than anything out there, but does it -actually- use quantum tunneling?  That's something that is under very hot debate at the moment.


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## morbit (Oct 10, 2013)

Are you living under a rock? 

http://www.wired.com/wiredenterprise/2013/06/d-wave-quantum-computer-usc/


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## kpedersen (Oct 10, 2013)

http://www.dwavesys.com/en/products-services.html

You can even buy one apparently


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## Whattteva (Oct 10, 2013)

I like to aim for a more modest (baby step) goal from a consumer stand-point (It is essentially useless to me if I can't afford it, irrespective of its prowess). I would be much much much happier if they just manage to find a way to reach superconductivity without having to sink too far beyond room temperature. This would enable much more practical, faster, and much more power efficient computers to be mass-produced for us consumers to use.

Once they've figured that out, then they can continue moving on to larger things.


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## zspider (Oct 10, 2013)

I'm not confident I'll ever live to see a practical quantum computer in my lifetime either.


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## Crivens (Oct 11, 2013)

If there is such a thing as a working quantum computer (or will ever be), they will be big, expensive, and classified. It will take years, decades or longer for them to become a device that can be bought by individuals.


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## davidNwillems (Feb 4, 2016)

I have a question. Let us try to have a Quantum computer pick 1 path among X total paths. Only 1 is the correct choice, to be based on an extensive ‘search calculation’ which can be left undefined for this example. How big does X need to be to bomb-out a quantum computer? Meaning too many paths to do simultaneously, forcing the computer to drop down into ‘normal’ mode from ‘quantum’ mode. Does anyone know this or know where I should ask? Thanks in advance.


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## ANOKNUSA (Feb 5, 2016)

davidNwillems, did you sign up here and bump a two-year-old thread just to get help on a homework assignment?


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