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## Under the Hood of Quantum Computing156

Posted by ScuttleMonkey
from the fun-facts dept.
nanotrends writes "Gordie Rose, the CTO of Dwave Systems, the venture funded company that plans to offer paid use of a superconducting quantum computer starting in 2007, reveals secrets of his quantum computer construction. It is based on nobium superconducting 'circuits of atoms' and is not RSFQ. (Rapid Single Flux quantum)."
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## Under the Hood of Quantum Computing

on Sunday August 20, 2006 @07:11AM (#15943598) Homepage
I read the article, but it didn't make it very clear - what will be the advantages of paid use of their quantum computer? Unless it's going to be faster than other supercomputers, I can't see the point.

Well, it's a quantum computer. Given the problem it might be like trying to make your CPU compete against a GeForce or ATI. If you try to do it all with CPU emulation, there's not much doubt who'll win. That said, I got the impression that current quantum computers have a so limited number of qbits (the computing power pretty much grows to 2^n with n bits), that it's faster and cheaper to just cycle through all 2^n possibilties one at a time. Currently the largest I've seen is a 12 qbit computer [blogspot.com]. Now 2^12 = 4096 states at once is a nice curiosity but nothing that makes my encryption keys worry. Basicly it's man vs Deep Blue at computer again - the quantum computer is great at testing many solutions at once but the sheer computing power of traditional computers takes home the victory. Now, if they can get hundreds of qbits together things will change massively. But the difficulty in keeping all those in a cohesive quantum state also raise drastically, so I think we're far off from a usable quantum computer.
• #### Re:RTFA, WTF? (Score:4, Informative)

on Sunday August 20, 2006 @07:12AM (#15943603)
... What have I missed here?

For starters; a link to the company's website instead of somebody's "See Spot run" blog post:

http://www.dwavesys.com/quantumcomputing.php [dwavesys.com]

KFG

• #### Re:"Quantum" computer is misleading (Score:5, Informative)

on Sunday August 20, 2006 @07:28AM (#15943619)
From dwave's site: "There are many potential ways to build quantum computers (QCs). Of these, four types have emerged as being most likely to succeed. These are based on (A) assemblies of individual atoms trapped by lasers; (B) optical circuits, for example using photonic crystals; (C) semiconductor-based designs, usually including atomic-scale control of dopant atom distribution or quantum dots; and (D) superconducting electronics. D-Wave focuses exclusively on superconducting electronics. This is because superconductors have the unique property that very large structures can be built out of them that behave according to the rules of quantum mechanics. Because of this, design of superconducting QCs does not require new technology development. This is in contrast to the other three types of QCs, in which information is stored using atoms or individual photons (particles of light), and controlling and manipulating this information requires technologies that do not yet exist. The two superconductors used to build QCs are aluminum and niobium. At room temperature these materials are metals. When they are cooled down close to absolute zero, the electrons in the metals pair to form particles called Cooper pairs. These particles carry charge in the superconductor. Cooper pairs are very different from electrons. One key difference is that Cooper pairs are what physicists call bosons, while electrons are fermions. Bosons are allowed to occupy the same quantum state, while fermions are not. In a superconductor, all the Cooper pairs can (and do) exist in exactly the same state. This means that all of the charge carriers in the superconductor are fundamentally linked. They directly inherit their behavior from the scale of a single Cooper pair. One way to think of this is that a chunk of superconductor amplifies the quantum effects that exist at the level of extremely tiny individual particles up to the scale of the whole chunk, even if the chunk is very large. This amplification of quantum effects is responsible for the well-known properties of superconductors, such as zero resistance to current flow and exclusion of magnetic field. It is also extremely useful for building components of QCs. Superconductors naturally shield themselves from external noise, creating a safe haven for quantum effects. This ability to build large things that behave like small things overcomes many practical problems in building real QCs."

on Sunday August 20, 2006 @07:52AM (#15943662)
"Now, if they can get hundreds of qbits together things will change massively."

I think the point of the article is that D-Wave Corp claims to be able to create qbits from "large" objects (ie; large enough to be fabricated using standard IC fabrication techniques), but with niobium rather than silicon. This enables them to create a quantum computer without all the hassle of having to manipulate individual atoms as the present research lab quantum computers do. From the article:

Superconductors are the only type of material that we know of where big lithographically defined devices (like really big. Like centimeter on a side big.) can be built that behave just like they were atomic-sized.

Since supercooling is required, it's highly unlikely that you or I will be able to afford one of these things any time soon (assuming it's not all marketing hype in the first place), but you can be assured the NSA and other government "intelligence" agencies will be able to afford as many as they want because of all the tribute they demand from us on pain of imprisonment, in the form of exorbitant taxation.

<paul@prescod. n e t> on Sunday August 20, 2006 @07:58AM (#15943677)

I read the article, but it didn't make it very clear - what will be the advantages of paid use of their quantum computer? Unless it's going to be faster than other supercomputers, I can't see the point. Is there some other advantage I'm not aware of?

Yes, of course the goal is to be substantially faster than other supercomputers: for certain classes of problems. These are outlined on the company's website ( http://www.dwavesys.com/optimization.php [dwavesys.com] ) and ( http://www.dwavesys.com/quantumcomputing.php [dwavesys.com] ). But if you want a "Neutral Point of View" , I'll quote wikipedia:

It is widely believed that if large-scale quantum computers can be built, they will be able to solve certain problems faster than any classical computer...
Integer factorization is believed to be computationally infeasible with an ordinary computer for large numbers that are the product of two prime numbers of roughly equal size (e.g., products of two 300-digit primes). By comparison, a quantum computer could solve this problem relatively easily. If a number has n bits (is n digits long when written in the binary numeral system), then a quantum computer with just over 2n qubits can use Shor's algorithm to find its factors. It can also solve a related problem called the discrete logarithm problem. This ability would allow a quantum computer to "break" many of the cryptographic systems in use today, in the sense that there would be a relatively fast (polynomial time in n) algorithm for solving the problem....
This dramatic advantage of quantum computers is currently known to exist for only those three problems: factoring, discrete logarithm, and quantum physics simulations. However, there is no proof that the advantage is real: an equally fast classical algorithm may still be discovered (though some consider this unlikely). There is one other problem where quantum computers have a smaller, though significant (quadratic) advantage. It is quantum database search, and can be solved by Grover's algorithm. In this case the advantage is provable. This establishes beyond doubt that (ideal) quantum computers are superior to classical computers.

From D-Wave's website:

For several decades, computer scientists have been trying to classify all of the problems we know of. Whenever a new problem comes up, it is placed in one of the existing categories of problems. These categories describe how difficult the problems within it are, and why.

One of the most interesting categories contains problems that are called NP-complete. These all have the feature that in order to solve the problem all possible solutions must be tried, and the number of possible solutions grows exponentially with the problem size.

An example is the Travelling Salesman Problem, although there are literally thousands of them. This category is a particularly interesting target from a commercial perspective because most real-life business problems are in it.

...

Quantum computers can be used to get approximate solutions to large NP-complete optimization problems much more quickly than the best known methods running on any supercomputer.

• #### It just sounds a lot like a RSFQ chip. (Score:4, Informative)

on Sunday August 20, 2006 @08:24AM (#15943721)
From what has been described on the blog and website, i'm not convinced that what they're working on is much more than simply a superconducting RSFQ - Rapid Single Flux Quantum - chip, which although can concievably run at a breakneck speed compared to todays Silicon CPU's, is not a Quantum Computer in the normal sense. This thing isn't going to run Shor's Algorithm. Also, i'm surprised to notice that there are people here who still consider QCs as science fiction - they're not. Quantum Computing has been practical in the lab since the 90's - and, for example, composite numbers have been factorised in polynomial time. The challenge faced by QCT research groups around the world at present is mainly building the things with a large number of qubits, and still maintaining successful operation. With regards to solid state devices such as the Kane QC model, one of the approaches being investigated involves building multiple small QCs and interconnecting them via conventional microelectronics - perhaps SETs, RSFQs, spintronics or maybe even plain old silicon microelectronics - to create a useful, many-qubit, computer.
• #### ACK (Score:3, Informative)

by Anonymous Coward on Sunday August 20, 2006 @08:31AM (#15943736)
As a physicist who had courses in Quantum Computation I had to vomit when I just read the Title Superconducting Quantum Computer.

There are only two Quantum Algorithms with applications in real live AFAIK Shor's factoring Algorithm to find the Prime Factors of a number in polynomial time, and a boosted search algorithm, which gives a \sqrt(O) speed boost. The largest number Shor's Algorithm could be used on is 15. And it won't be usefull before we reach 16 bit's or so (which we won't in my lifetime with any of the approaches discussed today). The larges stable aray of qubits is 8 AFAIK, and you cannot do anything with those so far everybody is just working on stbility and prooves of concept.

1) Hence there is no usefull quantum computer in existence. Anyone who want's to sell you one is a liar.

Superconductivity, is well known and not very hard to achieve. I can make pretty much any material superconducting if you just give me a liquid Helium 3/4 demixer. So once I have a working quantum computer, I can add some lead, empty a bottle of Liquid Helium over it, and claim, that I have a super conducting Quantum computer. To be fair it's often inherent in the design of a Quantum computer that it needs to be very cold. But it doesn't always need to be so. But what remains is

2) Saying a quantum computer is superconducting doesn't add any infomation about the usefullness of such a device.

So what could this headline mean:
Someone allows you to use his NMR (Nuclear Magnetic Resonance) device if you give him money.

(NMR is standard in todays chemistry labs, and very simple useless quantum algorithms (see "Deutsch algorithm") have been implemented with it.)

Where is the beef? Can an article still be kicked out at this stage?

on Sunday August 20, 2006 @09:12AM (#15943806) Journal
As far as I know, only RSA-style cryptograophy is affected by quantum computing. There are other ways to do public key encryption, such as elliptical curve cryptography [wikipedia.org] that should be unaffected, as they depend on a different class of problem being hard, and of course quantum computing won't help with symmetric key crypto at all.

The NSA has been advising the security community against using RSA-style encryption for some time now - it's not like they're trying to keep the weakness a secret for some nefarious reason.
• #### QP =? NP (Score:3, Informative)

<benjaminhocking@ ... om minus painter> on Sunday August 20, 2006 @10:14AM (#15943945) Homepage Journal
Actually, it would mean that QP = NP. This is considered more likely than P = NP, but as with P=?NP no one has yet shown it to be true or false.

on Sunday August 20, 2006 @10:14AM (#15943947)
I do believe you're mistaken. Quantum bits are exactly like regular bits in their possible observable states - that is, they are either "on" or "off" when observed. The interesting part of quantum computing comes from the fact that, when they're not being observed, they exist in a superposition of both "on" and "off" states. Now, if you put 8 of these bits together, you have a 'qbyte' which, while when it's observed it can only represent the same range as a regular byte, can be used in calculations representing every single possible permutation of the data at once - i.e. every number from 0 through 255. Each bit you add doubles the number of states you can simultaneously test using this superposition property - this is what the GP meant when he said that quantum computing scales as 2^n.

on Sunday August 20, 2006 @11:39AM (#15944165)
That sounds rather stupid. Why only test for "on" or "off" when you can test for any of the states?

Two points: what other states, and how do you propose we measure them? Quantum bits will typically have only the 1/on and 0/off states, by design - partly because it meshes well with our classical computing methods, and partly because most make use of concepts like spin which are naturally in up/down or the like. When isolated, they evolve into a state expressed by a|0> + b|1>, where a and b are the probability that you will observe the 0 state or the 1 state, respectively. This superposition state is impossible to observe, since the wavefunction collapses into one or the other on observation, so we can only observe either the 1 or the 0. More generally, you have a state for the entire register which is the superposition of every possible 'classical' state, with individual probabilities of being observed when you check the register of a, b, c and so forth.

Also, your post makes little since, everything is observed, which is why it exists, just because it isent observed by humans dosent mean its not observed,

This is very true, in general, and is the very reason why quantum computing is hard. The qubits have to be completely isolated from everything except the read/write mechanism, so that these particles will only be observed by humans, and nothing else, otherwise many of the requirements to make a quantum computer effective cannot be reasonably achieved.

• #### Complete nonsense (Score:1, Informative)

by Anonymous Coward on Sunday August 20, 2006 @11:54AM (#15944194)
This article is total crap. IAAP (figure it out) in the field of spin based electronics, closely aligned with efforts to develop qc. As described in the article, these circuits are not quantum bits. Nb metal that is held at low temp will enter the so called "ground state" of the material where all electrons are in a single state. Great. you have a macroscopic quantum state. Problem is that superconducting states do not exist outside of the superconducting metal. in fact they have a region of "normal state" i.e. non-superconducting electrons that forms a small skin on the outside of the material. This is mostly the result of disorder in the material, thermal fluctuations etc. This means that if you hare trying to create 2 q-bits in this way, you will have trouble "coupling" them together. if there is no coupling, no information transfer, no interaction, and no "computation". Building q-bits is easy, anyone can do it. Coupling q-bits and controling that coupling interaction is the hard part. superconducting states cannot couple to each other if they are discrete disconnected structures. This article is total bs. inverstors beware.
• #### MIT Technology Review Article on DWave (Score:4, Informative)

on Sunday August 20, 2006 @11:56AM (#15944200)

Computers have infiltrated nearly every field of business and science, and they keep getting faster. Nonetheless, researchers routinely encounter problems impossible for even the most powerful supercomputers to solve. The remedy could be quantum computers, which would use the fantastic properties of quantum mechanics to crack such problems in seconds rather than centuries. Since the 1980s, physicists in academic labs and at firms such as IBM, Hewlett-Packard, and NEC have pursued a variety of quantum computing approaches, but none seems likely to deliver a working machine in less than 10 years.

Company: D-Wave Systems

Amount invested: $22 million Canadian (about$17.5 million U.S.)

Key founders: Geordie Rose, Alexandre Zagoskin, Bob Wiens, Haig Farris

Technology: Quantum computers

Vancouver startup D-Wave Systems, however, aims to build a quantum computer within three years. It won't be a fully functional quantum computer of the sort long envisioned; but D-Wave is on track to produce a special-purpose, "noisy" piece of quantum hardware that could solve many of the physical-simulation problems that stump today's computers, says David Meyer, a mathematician working on quantum algorithms at the University of California, San Diego.

The difference between D-Wave's system and other quantum computer designs is the particular properties of quantum mechanics that they exploit. Other systems rely on a property called entanglement, which says that any two particles that have interacted in the past, even if now spatially separated, may still influence each other's states. But that interdependence is easily disrupted by the particles' interactions with their environment. In contrast, D-Wave's design takes advantage of the far more robust property of quantum physics known as quantum tunneling, which allows particles to "magically" hop from one location to another.

Incorporated in April 1999, D-Wave originated as a series of conversations among students and lecturers at the University of British Columbia. Over the years, it has amassed intellectual property and narrowed its focus, while attracting almost \$18 million in funding, initially from angel investors and more recently from the Canadian and German governments, and from venture capital firms. The company plans to complete a prototype device by the end of 2006; a version capable of solving commercial problems could be ready by 2008, says president and CEO Geordie Rose.

The aggressiveness of D-Wave's timetable is made possible by the simplicity of its device's design: an analog chip made of low-temperature superconductors. The chip must be cooled to -269 C with liquid helium, but it doesn't require the delicate state-of-the-art lasers, vacuum pumps, and other exotic machinery that other quantum computers need.

The design is also amenable to the lithography techniques used to make standard computer chips, further simplifying fabrication. D-Wave patterns an array of loops of low-temperature superconductors such as aluminum and niobium onto a chip. When electricity flows through them, the loops act like tiny magnets. Two refrigerator magnets will naturally flip so that they stick together, minimizing the energy between them. The loops in D-Wave's chip behave similarly, "flipping" the direction of current flow from clockwise to counterclockwise to minimize the magnetic flux between them. Depending on t

• #### Re:Woo Woo science (Score:3, Informative)

on Sunday August 20, 2006 @12:47PM (#15944372)
Maybe you should look into this really nice bunch of intros to quantum computing. [qubit.org] (Click on "Tutorials").
• #### I guess Josephson junctions and/or vaporware (Score:3, Informative)

on Sunday August 20, 2006 @12:51PM (#15944391)
This smells vaguely like vaporware. At least none of the speakers at this years or last years Spin and Qubit conference [isis.ku.dk] seemed nearly as optimistic as these guys, even though there were several top notch people (and last year the focus was VERY much quantum computing).

In any case, the technology that comes to mind when I hear "very cold superconducting niobium quantum computer" is Josephson junctions [wikipedia.org]. There's an article on it here [arxiv.org].

What people does DWave have? What have they published previously?
• #### I would be surprised it they manage.... (Score:2, Informative)

on Sunday August 20, 2006 @04:20PM (#15945100) Journal
to build a working Quantum Computer until 2007. It would be a nice surprise, actually....

As a small disclaimer: I work in QC field. There are a few approaches to building a superconducting quantum computer, but there are not many experiments coupling even two Qubits. One paper discussing one of the few experiments which worked is:

But there are severe problems with superconducting qubits, namely that the quality of the insulators used in standard processes are not good enough for building a working QC right now.
(http://eiffel.ps.uci.edu/cyu/publications/qubit.p df#search=%22mooji%20qubit%22,

It's not that these fundamental problems could not be adressed by developing better insulators or using other approaches
(http://www.solid.phys.ethz.ch/wallraff/content/sc ience/QuantumComp.html, http://link.aps.org/doi/10.1103/PhysRevLett.95.210 503 [aps.org]), but it is unlikely that any quantum computer will provide cheaper computing power for NP-hard problems than the cell processor until quite a while from now. In my personal opinion and also the opinion of some other people which i talked to is that the timescale for that is something like 10-15years of intense research.

But indeed, superconductors are one of the best candidates (others: atom traps etc.).

The role of D-Wave is that they are trying to push the development of superconducting QC to something which can be sold or where at least the patents can be sold. So it is natural (and probably good) that the external represantation on what they got is optimistic. But maybe it is important to point out to the slashdot readers that the blog of the CEO of a company is for sure an optimistic assumption what the future may hold and not the full criticism imposed by a peer-review in a scientific journal........

Another thing which makes it difficult to assess what they got is that D-Wave is usually pretty uninformative about what their specific plans are. Thats understandable because they spend a lot of money (for a company) into something where they will get out patents which would be weakened by prior art if they talk to loud.
• #### "like getting two qubits to interact..." (Score:3, Informative)

on Sunday August 20, 2006 @10:33PM (#15946230) Homepage
Check out the sidebar under "Published Stuff", especially this [arxiv.org] link... Next objection, please...

Paul B.
• #### Re:I think it will. (Score:3, Informative)

on Monday August 21, 2006 @12:26AM (#15946555)

A Brief History of Quantum Computing [ic.ac.uk] contradicts all your quantum-computing assertions: "In effect, a calculation performed on the register is a calculation performed on every possible value that register can represent." That's in its description of Shor's algorithm, which also contradicts your feedback-driven characterization, saying it produces very-likely factors and succeeds by simply retrying until one of its answers works.

That link also describes Grover's algorithm, cutting brute-force search from O(N) to O(N^0.5). That alone is enough to put AES-128 in range of today's horsepower (but not enough to reach AES-256). Maybe it's provably impossible to reduce symmetric decryption to less than linear search, I don't know.

The number of plausible-but-wrong decryptions of a cipher block you know the plaintext for is zero, so unicity distance is only trivially relevant; if you insist, we can say it's exactly the cipher block size regardless of the plaintext language in this specific case.

on Monday August 21, 2006 @02:36AM (#15946872)
That's not really how quantum mechanics works.

Everything is not observed. It cannot be observed. Mathematically there are certain things that cannot be observed, but that still exist, and can still be interacted with.

The mathematics of quantum mechanics suggests that certain things happen so long as there's no attempt to observe them. There are all sorts of crazy experiments that verify this result, but in summary it's as you read: under quantum mechanics there are things that are certain ways only so long as you don't look.

Before you think this is all hogwash, quantum mechanics is actually one of most successful theories that physics has ever proposed.

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