# Toward On-Chip Quantum Computing

#### CmdrTaco posted more than 6 years ago | from the a-laudable-goal dept.

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."*

## Hmm... (1, Funny)

## jrothwell97 (968062) | more than 6 years ago | (#21708780)

## Re:Hmm... (1)

## looseSpark (1012149) | more than 6 years ago | (#21708922)

## QC = 100% Bullshit (0, Troll)

## MOBE2001 (263700) | more than 6 years ago | (#21709508)

This post is both in the state of being the first and not the first post until I hit the submit button and decide the outcome by refreshing the page. That's quantum computing.Yeah. That's quantum computing alright, 100% bullshit [blogspot.com] . Now you idiots can mod me down as a troll but it's still bullshit. ahahaha...

## Run! (1)

## mstahl (701501) | more than 5 years ago | (#21715654)

Quantum trolling! It has begun....

## Relief (1)

## bdesham (533897) | more than 6 years ago | (#21708840)

## Questions of SW developer (1)

## should_be_linear (779431) | more than 6 years ago | (#21708878)

## Re:Questions of SW developer (-1, Troll)

## Anonymous Coward | more than 6 years ago | (#21708932)

I hope it will result in radical new software that can teach you English. Don't waste our time here if you write so poorly.

## Re:Questions of SW developer (2, Insightful)

## QuickFox (311231) | more than 6 years ago | (#21709058)

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

## Re:Questions of SW developer (-1)

## rucs_hack (784150) | more than 6 years ago | (#21709308)

For example, does it mean traditional programming languages will be modified, handling of variables will be different, maybe new operators?It does mean that the traditional view of the operating system will change, and that might change programming languages. A variable will still be a variable, same for constants, and when it comes down to it there are very few actual operators. I'm not aware of quantum mechanics introducing any new operators, so I can't see that they would be needed for quantum computing. It could be that the way we use them use will radically change.

Will it be able to solve Traveling Salesman in linear (or constant)time?TSP is NP-hard, so yes, it's tricky, but what do you mean solve? You mean as in if your solution is true for

ncities it will remain true forn+1?Any computer can

dothe TSP, so I guess you mean, could a quantum computer calculate a superior answer to the TSP for a large value ofn. One assumes you also mean 'and do it quicker'. And the answer is, I'm buggered if I know.Is it able to solve chess game?Chess, aside from being Zero Sum, does not have a single solution in the classic sense, such that it could be said to be solved that I am ware of. Any single solution, once described, could be negated (beaten) because of the extremely large combination of possible configurations possible on a chess board, and not all pieces move the same way. I seriously doubt there is one unbeatable strategy, since a player cannot control the first piece the other player moves.

## Re:Questions of SW developer (4, Informative)

## exp(pi*sqrt(163)) (613870) | more than 6 years ago | (#21709642)

> 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.

## Re:Questions of SW developer (-1, Troll)

## rucs_hack (784150) | more than 6 years ago | (#21709720)

## Re:Questions of SW developer (1)

## exp(pi*sqrt(163)) (613870) | more than 6 years ago | (#21711044)

## Re:Questions of SW developer (0, Flamebait)

## rucs_hack (784150) | more than 6 years ago | (#21712812)

## Re:Questions of SW developer (1)

## Poromenos1 (830658) | more than 6 years ago | (#21710164)

## Re:Questions of SW developer (1)

## exp(pi*sqrt(163)) (613870) | more than 6 years ago | (#21711008)

## Re:Questions of SW developer (0)

## Anonymous Coward | more than 6 years ago | (#21724180)

Wikipedia disagrees with your definition of zero-sum, and states that chess is, in fact, a zero-sum game.Not any more

[Sincerely,

Mass Communications Officer,

Guantanamo Bay,

USA^WCuba

Approved by: Police State Dept/Minitrue]

## The concept of a variable (1)

## mangu (126918) | more than 6 years ago | (#21710498)

Let me guess, would those new operators be something like this? [google.com]

The article you linked is strangely amateurish for someone who claims to know so much about quantum mechanics. To get a better grasp on the difference between quantum

mechanicsand quantumcomputing, I suggest that you start here. [wikipedia.org] As you say, let's try to raise the signal to noise ratio here.## Re:The concept of a variable (1)

## exp(pi*sqrt(163)) (613870) | more than 6 years ago | (#21710846)

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 ingredient).

I was hoping to find a good "square root of not" article on Wikipedia but I settled for the American Scientist one. I think it's not bad, in the sense that it doesn't bombard the reader with too much theory, but when you come away from it you may be able to start playing with the ideas yourself (make sure you get past page 1 of course). If you know better, please post here.

## Re:The concept of a variable (1)

## blueg3 (192743) | more than 6 years ago | (#21711060)

## Re:The concept of a variable (1)

## maxwell demon (590494) | more than 6 years ago | (#21712972)

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:The concept of a variable (1)

## blueg3 (192743) | more than 5 years ago | (#21714792)

## Re:The concept of a variable (1)

## maxwell demon (590494) | more than 5 years ago | (#21717990)

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 Hadamard operator should be more fundamental than the square root of CNOT, the phase gate, or any other non-classical one-qubit operator.

You're right that it has no classical equivalent. Nor has sqrt(NOT), phase shift, or any other one-qubit operation other than the identity and NOT.

## Re:Questions of SW developer (2, Interesting)

## blueg3 (192743) | more than 6 years ago | (#21709528)

I don't remember offhand the set of problems that are trivialized by quantum computing, but the difficulty of many problems changes drastically. For example, you can find an element in an unsorted array using a quantum computer in constant time.

## Re:Questions of SW developer (1)

## maxwell demon (590494) | more than 6 years ago | (#21712868)

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 more powerful (but how much more powerful isn't yet known; it gets exponential speedup for factorization relative to the known classical algorithms, but there's not yet any proof that there's no classical algorithm which could do that as well; however database search can be speeded up from O(N) to O(sqrt(N)), so there's definitively speedup).

No, just in O(sqrt(N)) time.

## Re:Questions of SW developer (1)

## blueg3 (192743) | more than 5 years ago | (#21714804)

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").

## Re:Questions of SW developer (1)

## kryten_nl (863119) | more than 6 years ago | (#21709594)

## Re:Questions of SW developer (1)

## Jeff DeMaagd (2015) | more than 6 years ago | (#21709616)

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

## Enleth (947766) | more than 6 years ago | (#21708956)

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...

## Re:Looks like /. stories have quantum states, too. (2, Funny)

## FST (766202) | more than 6 years ago | (#21709046)

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

## maxwell demon (590494) | more than 6 years ago | (#21712990)

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

## Jimminey Cricket (224848) | more than 6 years ago | (#21709020)

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).

## Re:free first submission of other article (1)

## ibillin (1203690) | more than 6 years ago | (#21710404)

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

## maciarc (1094767) | more than 6 years ago | (#21709084)

## Quantum Crystal Computers? (1)

## MikeUW (999162) | more than 6 years ago | (#21709114)

## Re:Quantum Crystal Computers? (0)

## Anonymous Coward | more than 6 years ago | (#21709354)

## It's Obvious......I should have waited (1)

## hyades1 (1149581) | more than 6 years ago | (#21709410)

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.

## Re:It's Obvious......I should have waited (1)

## kryten_nl (863119) | more than 6 years ago | (#21709630)

## Re:It's Obvious......I should have waited (1)

## hyades1 (1149581) | more than 6 years ago | (#21709670)

## decryption (1)

## cadeon (977561) | more than 6 years ago | (#21710144)

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't require ever-expanding key sizes?

## Re:decryption (1)

## ibillin (1203690) | more than 6 years ago | (#21710578)

## Nonsense (0)

## Anonymous Coward | more than 6 years ago | (#21710170)

Uh, vacuum tubes and transistors work with QM principles.

## Exponentially more difficult to build? (1)

## BlueParrot (965239) | more than 6 years ago | (#21710172)

Has this issue been resolved yet ? If not it appears that you would just be gaining performance at the expense of reliability. 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. I seem to remember that there were more fault resistant QC schemes, but that they suffered memory needed instead (i.e, performance and stability scales, but number of qubits needed does not ). Obviously that would cause just as many problems since running rapidly with a large amount of memory would have to compete against several slow machines in parallel.

As much of a nuisance as it would be, it appears quite plausible that quantum computers might have a "tradeof" relation of some sort, similar to the uncertainty principle. Something along the lines of:

S*E*t*M*T > C

Where S is the complexity of the problem, E is energy needed, t is time to complete a calculation, M is the amount of memory needed (roughly the mass of the computer ), T is temperature, and C is a non-zero constant. It is pure speculation of course, and even if it turns out to be true C might be very small (i.e M = 1kg might be absolutely massive when measured on atomic scales ), but there could be a lot of catches to scaling these things...

## Re:Exponentially more difficult to build? (1)

## Soleen (925936) | more than 6 years ago | (#21710678)

<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.

## Re:Exponentially more difficult to build? (1)

## SeekerDarksteel (896422) | more than 6 years ago | (#21711442)

## Energy required exponential? (1)

## Myria (562655) | more than 6 years ago | (#21710660)

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

## What doesn't obey QM ? (1)

## noshellswill (598066) | more than 6 years ago | (#21711902)

## Reversible Logic Synthesis (1)

## kEnder242 (262421) | more than 6 years ago | (#21712446)

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 (1)

## Team Zissou (887422) | more than 6 years ago | (#21712900)