Quantum computers

[pulkit]

Quantum computers

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In a recent college lecture, we were briefly introduced to the concept of quantum computers......
Frankly at first it all seemed out of a science fiction novel, a computer being in various states at once and the concept of a Qubit.......
Could ne1 please tell me how far do we stand today in this field, and wat sort of technology has yet been achieved, becoz as far as I know there have already been some interesting algorithms written to run on q-computers

[timo]

Heard a speech about quantum computing but since that was at least one year ago I can´t remember much. If I remember correctly the professor holding that speech (don´t even know where he came from) was experimenting with an atomic quantum computer (dunno which kind of atoms or even if it was single atoms - was defenitely not photons). They used 4-6 atoms each of them most probably a single qbit. I don´t think many of the algorithms written for quantum computers have yet been implemented (if the factorization of large numbers had been done one would have certainly heard about it) because it´s quite easy to design an algorithm theoretically when one doesn´t have to care about the huge problems in implementation. Interaction with enviroment for atomic Quantum Computers and lack of ideal optic materials for photonic ones would come to my mind, here.

Since I can´t tell you much about this topic I can at least give you a link that might help you:
http://theory.caltech.edu/people/preskill/ph229/

[pulkit]

About the algorithms, I am pretty sure that one for factoring large numbers has been figured out. This is primarily why I find this field extremely fascinating, becoz such an algorithm wud immediately mean that the popular RSA system of encryption wud be rendered completely useless

It still however seems to be a field in which a lot of research is happening and there isn't too much text available in print

[ed84c]

It is possible to build a computer (quantum) that could work out every possible calculation simulataneously, without too much hastle, but would we understand the answers as the calculations become more and more complicated?

Anyway the problem that computers have at the moment is that they use electricity.
A computer that uses fibre optics and cables would far exceed anything an Electrical computer could perform.

[e(ho0n3]

Originally Posted by pulkit

Could ne1 please tell me how far do we stand today in this field, and wat sort of technology has yet been achieved, becoz as far as I know there have already been some interesting algorithms written to run on q-computers

The majority of the research being done in this field today is in the construction of quantum computers, particularly with the use of quantum optics. There are of course other ways to build a quantum computer.

It still however seems to be a field in which a lot of research is happening and there isn't too much text available in print

The amount of books on this subject is growing and I keep seeing more and more research articles about this subject almost every day.

I guess everybody knows about Shor's prime factorization algorithm. Apparently Shor has become famous. Isn't he teaching at MIT now?

One of the problem plauging quatum computers is the Uncertainty Principle, i.e. measuring the results of a quantum computation directly will destroy the results.

To study any kind of quantum mechanical system via experimentation requires that one isolate the system completely from any outside contamination. This is the other problem in the field and has lead to the creation of what is known as quantum error-correction coding.

[fuhrerkeebs]

We've built quantum computers...but they are so elementary right now that they are useless.

[pulkit]

We have built them ? If there exsists one, how many qubits does it have ?

[fuhrerkeebs]

2 qubits. It was built by MIT researchers.

[fuhrerkeebs]

http://web.mit.edu/newsoffice/tt/199...4/quantum.html

[5614]

Originally Posted by fuhrerkeebs

2 qubits. It was built by MIT researchers.

now, that, is a slow computer!

i thought they were a bit faster than that. still, at the moment it is all potential.

my ownly draw-back with these is this:

in normal computers, data is registered in binary, 1s and 0s, as it will be in quantum computers, however, there are 8 bits in a byte, 1,000,000 bytes [million] in a megabyte, and 1000MB in a gigabyte [all approx]
but you know that, my point is this, most programs are sized in GB now, that is a lot of bits! these computers have so far to advance, until they outstrip our computers today,
how will they computer be able to measure the properties of that amount of atoms, [which represent the data] quicker than our normal computers of today?
isnt that a long way into the future?

what do you lot think?

[5614]

http://www.newscientist.com/news/news.jsp?id=ns9999340

is about an experiment for quantum computing, in which they stopped light, read the article for more info.

[TheProphet]

Well due too the Qm cumputers emence capacity if realised in 40q:s as the example was then i most shurely belive that none of us is going te get our hands on it! Since all governments will stop it untill they have a security system that the Qm cp won't breach!

[5614]

why do you think that quantum computing will easily hack government stuff? because of it vast speeds, it could go through millions of passwords a second? maybe!?

additionally, it would be hard to stop someone selling something, unless they are deemed a national security hazard! which they could be. but it would be such a big breakthrough in science, every physicist in the world would want to see it! and the public demand would be massive, it would soon become a billion-pound business. not that easy to restrict!

[pulkit]

why do you think that quantum computing will easily hack government stuff? because of it vast speeds, it could go through millions of passwords a second? maybe!?

Well thats because Peter Shore came up with an algorithm to crack RSA cryptography system which can be realised using quantum somputers.
RSA is what pretty much every application uses for secure data transfers like passwords, credit card nos etc.

[5614]

yeah, i'd heard of it, quite why all apps use RSA i dont know, now its cracked and all! although not many ppl try and hack the apps... spose there arent many popular alternatives.

[pulkit]

It is impossible to crak using current computer systems.
It is an ingenious method of encryption, I made a an RSA cryptosystem once, the mathematics involved is not extremely difficult, but the fact is to crack it you need know how to factorize large numbers into prime factors, thats what Shore's algorithm does.

[Cap'n Refsmmat]

What's impossible to crack? I don't know about this system.
In theory it is possible to crack any code except for a single-time pad which uses a never-repeating key, and is only used once.

[5614]

agreed, pulkit, any system can be cracked, as can any code, any program, or any protected file, what are you talking about?

[Cap'n Refsmmat]

Originally Posted by 5614

agreed, pulkit, any system can be cracked, as can any code, any program, or any protected file, what are you talking about?

Well, almost. If you give the person a key in advance that is non-repeating and you NEVER use it again, then it is impossible to break. But then you have to give him a new key every time, and to give him a new key means someone might intercept it and decode your message.

[pulkit]

When I say impossible, i mean if you employ the fastest super computer to try n crack RSA, it'll probably take time in years.
Problem : Factoring a 1024 bit or higher bit number. There is no known efficient way to do it. If you can figure out a way to do this, you'll probably become a billionaire in no time.

Using 100 digit or so prime numbers, RSA develops a function that is "impossible" to invert. If you know the inverse function you can decode. This inverse function determination needs prime factorisation.