## Toward On-Chip Quantum Computing 48 48

Darum writes

*"Researchers are working to create devices built on the rules of quantum mechanics. These would allow quantum computers which can do certain problems such as prime number factorization for decryption and simulation of complex systems (such as protein folding) in a tiny fraction of the time required on classical computers. Two papers appearing in this week's Nature raise the possibility of developing such quantum devices by manipulating light signals by semiconductor quantum dots. One of the approaches bases on photonic crystals, which seem pretty ideal for on-chip integration of a full set of computation components. One of the study's authors put up a good background story of this work on CVitae. The author discusses the potential simplicity and microchip scalability of these two quantum-dot 'light switch' systems. This could be good news for quantum information processing and ultra-secure long-distance communication applications. It could also allow all-optical signal processing, which has long been a holy grail for optical communications and could allow extremely fast and low-power optical interconnects."*
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## Run! (Score:2)

Quantum trolling! It has begun....

## Relief (Score:2)

## Questions of SW developer (Score:2)

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And when I say welcome, obviously I'm thinking of everyone except you. Asshole.

## Re:Questions of SW developer (Score:5, Informative)

> A variable will still be a variable

This is completely incorrect. The concept of a variable radically changes in a quantum computer because you are allowed superposed states.

> I'm not aware of quantum mechanics introducing any new operators

What in heaven's name are you imagining? Of course quantum mechanics introduces new operators. It completely turns classical mechanics on its head and introduces concepts that make no sense in a classical framework. Here's an example [americanscientist.org] of a specifically quantum operator.

TSP is NP-hard, and quantum computers don't, as far as we know, make NP-hard problems solvable in polynomial time. Grover's algorithm [wikipedia.org], however, does allow you to search a database of N items in time sqrt(N) so it could provide many speedups to familiar algorithms.

> Chess, aside from being Zero Sum

Are you *trying* to look like an ignoramus? Zero-sumness has absolutely nothing to do with chess. Zero-sumness is about the payoff you get from game of incomplete information. It has nothing to do with the strategy you should use in a game of complete information like chess. I guess you just want to sound smart by throwing around technical terms you don't grasp.

> seriously doubt there is one unbeatable strategy, since a player cannot control the first piece the other player moves.

Woah! Where are you getting this stuff from? Are you just making stuff up as you write it? It's incredible. Whether or not a game has a winning strategy has nothing to do with whether you can control the other player's first move.

As I say, there's nothing wrong with not knowing stuff. But spouting garbage in response to someone's genuinely inquiring questions is nothing short of obnoxious and just serves to lower the signal to noise ratio on Slashdot.

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## The concept of a variable (Score:2)

Let me guess, would those new operators be somethi

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No. Quantum computers are not just parallel computers and the new operations that quantum computing introduces are not simply parallel operations on arrays. (Is that what you were getting at?) If that were the case, Grover's algorithm would run in time O(1), not O(sqrt(N)). None of the nice quantum algorithms out there (eg. Grover's, Shor's) work simply because they do stuff in parallel (though doing stuff in parallel is an essential ingr

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thefundamental quantum operator is wrong. Indeed, there's not much you can do with only a Hadamard operator (applying it twice recovers your original state). And even if you combine Hadamard with the quantum versions of classical operators (like CNOT), you still don't get all possible quantum operations, not even approximately. You'll have to add another operation (like a phase shifter gate).## Re: (Score:2)

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How exactly do you propose to define the "fundamentalness" of a quantum operator? Basically an universal quantum computer needs to be able to do (at least approximately) any one-qubit unitary transformation (which can be done with Hadamard + phase shift, but equally well e.g. with square root of NOT and phase shift) and some non-trivial two-qubit operation (like CNOT). I don't see why the

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I don't rem

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That depends on your definition of "powerful". If "more powerful" means "can solve more problems", then no, the quantum computer cannot solve any problem which a classical computer cannot solve. If "more powerful" means "can solve problems in (asymptotically) less time", then yes, quantum computers can be mo

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Clearly in the above I was using the definition of powerful that makes sense, not the other typical definition ("capable of solving a larger body of problems").

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Is it able to solve chess game?.

"Solving" of the chess game like American Checkers was solved is not really a problem of computational speed (I mean it could be done by our civilization if we decided it would be worth it), but more of storage. There are more possible chess positions then there are atoms on Earth. http://en.wikipedia.org/wiki/Shannon_number [wikipedia.org] http://pages.prodigy.net/jhonig/bignum/qaearth.html [prodigy.net]

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## Looks like /. stories have quantum states, too. (Score:1)

This time, the cat is de... Er, the story is duped. Well, OK, not really an exact dupe, but looks like it references the same information, just from different sources...

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## free first submission of other article (Score:2, Informative)

http://arxiv.org/abs/0707.3311 [arxiv.org]

Reading the two papers careful, it turns out the photonic crystal paper is only at the "onset" of strong coupling (the decay rate is still about 2x faster than the coherent light-matter coupling rate) while the microdisk paper is actually strongly coupled (the coherent coupling rate is faster than any decay or dephasing).

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## Now all we need is... (Score:1)

## Quantum Crystal Computers? (Score:1)

## It's Obvious......I should have waited (Score:2)

You might notice that I posted basically the same feline reference twice a day ago under "Light-based Quantum Circuit Does Basic Maths".

Please apply one here, along with any obscure reference to quantum physics and/or time you may think appropriate.

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## decryption (Score:1)

As I understand it, encryption gets it's power from the fact that it takes a whole lot of computing power to guess the key, but if you have the key, everything goes well.

If everyone has these much more powerful computers, aren't we back to where we started? I'd think we'd end up at about the security level we are now, just with more overhead. Can quantum computing provide us with a new encryption method, which doesn'

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## Exponentially more difficult to build? (Score:2)

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<quote> Being able to factor large integers quickly is not much use if you have to repeat the calculation many times to make sure it was correct.</quote>

Wrong, it is usally much cheaper to check that answer is correct than to find the answer.

For example once quantum computer has factored a large number, it is simple to check the calculation even with regular PC by multiplying those numbers and compare with the orgincal large number.

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## Energy required exponential? (Score:2)

If such things are possible, I hope when the qubit count reaches ~2048 that someone factors the Xbox public key.

## Reversible Logic Synthesis (Score:2)

All about what you can and can't do with quantum computing (and how to implement it)

If you don't want to wade through everything, skip to Chapter 11.

http://books.google.com/books?id=0e8LbxngITsC&pg=PA229&dq=reversible+logic+synthesis&sig=l1bT9QLXAuEkhqLlmnU8gopwndY [google.com]

## All optical signal processing (Score:1)