How do qubits work and what are their pros and cons? What impact will they have on programming languages? [closed]_问答_开发者

Closed. This question needs to be more focused. It is not currently accepting answers.

Want to improve this question? Update the question so it focuses on one problem only by editing this post.

Closed 2 years ago.

开发者_Python百科 Improve this question

What can we do more with qubits than normal bits, and how do they work? I read about them some time ago, and it appears that qubits can store not just 0 or 1, but also 0 and 1 at the same time. I don't really understand how they work. Can someone please explain this to me?

What are their pros and cons, and what impact will they have on programming languages like C after quantum computers are actually invented?

How would we manage memory when a bit (which is also a quantum) can take multiple values at once? How can we determine if something is true or false, when there is more than just 1 and 0?

Any "classical" (as it will be called once the technology is in wider use) problem which is solved by "classical" code can be solved using some sort of quantum processor by transforming the problem. For example, to do a database search, instead of using an index-based search/binary search, or a linear search for an unsorted database, you can use Grover's algorithm. Also, to take a step back from the previous poster's mention of BQP problems, problems with a classical "solution" that runs in NP-time can be sped up considerably by Grover's algorithm (a speedup in the time to search through every possible solution). RSA cryptography is also made much more insecure by the advent of Shor's algorithm, since it makes factorising large numbers into their prime factors (the hinge upon which RSA sits) solvable in logarithmic time.

EDIT: Shor's algorithm actually runs in O((log N)^3), which is polynomial-over-logarithmic time.

The conclusion of this sort of thing is that pre-existing programming languages like C will not be able to be used on a quantum computer due to the nature of quantum algorithms (applying certain functions to quantum states), unless someone invents a way to map quantum gates and so forth to logical gates (EDIT: This has apparantly been mostly addressed here), in which case about all we get is a very very fast logical processor when using languages like C.

PS: I'm sure there'll be OpenGL bindings for quantum computing eventually :P

If we can make a working quantum computer (still an open question) then it can efficiently solve certain algorithmic problems that (we think) a classical computer cannot efficiently solve. These are the problems in the complexity class BQP but not in P. One big one is integer factorization. As Will A mentioned, if you can factor enormous integers quickly, you can break a lot of modern ciphers.

The catch is that nobody knows for sure if BQP is actually "bigger" than P — it might be that anything a quantum computer can do quickly, so can a classical computer.

We also don't know if BQP is as big as NP — for instance, nobody has found an efficient way to solve the Traveling Salesman Problem on a quantum computer. This is a common misconception about quantum computers. They might be able to do NP-complete problems quickly, and then again they might not. Nobody knows.

http://scottaaronson.com/blog/?p=208 be good readin' on this topic (as is the rest of the blog).

Regarding what can be solved with quantum computers: A quantum computer would break current asymmetric encryption schemes. It is a common misconception, that quantum computers can solve most optimization problems. They cannot. See this article for more details what can be solved using quantum computers and what cannot.

qubits doesn't store 0 and 1 simultaneously, actually they are made from the superposition of the 0 and 1 at a time. so if a normal bit can represent 0 or 1 at a time, but qubits contain 0 and 1 at a time. three normal bits can store any one of the following.... 000,001,010,...,111. but qubit can represent all of them at a time(which are in superposition). so a 'n' qubits store 2^n bits simultaneously!

Suppose a qubit an electron and it spins just like dipole momentum particle and when it spins it create an amplitude of multiple intensity and frequencies that minor amplitude can create spin vibration or momentum of particle that momentum can store thousand bits of information !!! (that's called quantum information processing) which is future !