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Light-Based Computers Using Quantum Principles
Maddog2030 cites a story at Science Daily, writing: "Here's an interesting twist to all the news on quantum computing. A computer running similarly to a quantum based computer, except it runs on light at similar speeds for particular tasks. It also rids itself of the many complications introduced by quantum computing."
"Wow, Fred... a new computer? Why did you trade in the red one for the blue one?"
"I didn't... try walking toward it."
A factor of a billion is inconsequential when considering 256-bit keys; after all, a billion is less than 30 bits, so it's equivalent to cracking a 226-bit key on a conventional computer.
The TWINKLE device by Prof. Shamir can be used to factorize relatively large numbers.
http://www.simovits.com/archive/twinkle.pdf
And to all the scepticals out there: There are results that show that QC can achieve better results that standard computation models (factoring is not one of them as we don't know its hard). We've only merged from the level of understanding quantum bits to the level of having a few interesting algorithms. Give it a few more years for digestion and we'll know much more about what can and what can not be done with "non-standrad" tecniques.
Can't wait for the light-based Tetris.
Word is the U.S. Military is working on a "super quantum" computer that sends its instructions faster than the speed of light. This way, in the event of a nuclear attack, we can hit a button that stops incoming missiles by blowing them up before they are ever launched.
Because it's cheating. First of all, because it has got nothing to do with quantum computing. Searching a database in parallel is only one aspect of quantum computing. Other aspects, like Shor's algorithm, totally depends on entanglement, which is something completely different from interfence. It's even worse, Shor's algorithm uses the fact that the combination of entangled states and partial measurements result in the destruction of interference. The second reason is that it will take you a rather long time to find out which of the 50 frequencies is altered. You have to do an interference measurements, which involves measuring light intensities with a moving detector. This is slower than a clasical computer.
The device in question works using interference of light waves, interference which can be described using a classical wave-only description of light: i.e. light can be treated as a wave propogating in a 3-d field of real-valued vectors that describe the magnitude and direction of E and H at each point in space.
This is in contrast to quantum interference, which generally involves the superpostion of state vectors in a Hilbert space (of complex valued wave functions).
-David
Cheggit out, here's the picture of the first computer bug ever:
Debugged.
-kidlinux.
I kind of like the mudslinging here between the quantum and optics camps, but has anybody else been troubled by the glossing over of spatial complexity here? Anybody can build a device that will solve a problem in one step. The spoiler is that the device will grow in size (or in this case, frequencies) proportional to the complexity of the problem. The QC paper on database searches did this: they claimed that a "conventional computer" could only search n items in O(n) time. But "conventional" devices have been built which find an item in O(1) time, eg by indexing the items by value. It seems like we have a mutually interfering group of entangled misconceptions here.
Heck, you could probably shoot radar at the surface of a hard disk and tune it to find a particular bit pattern, "billions of times faster". Would that violate "classical computing limits"? Not at all.
Overall, I would say that this is a step in the right direction. If you read the article you'll find that the stumbling block was that the optical crowd thought that the particles had to be entangled for a device to work. I suspect that this misunderstanding arose from Deutsch when he used the term incorrectly to describe a QC.
Maybe next they'll discover that a DRAM can fetch a value from any location *in one step*. My gosh, that's amazing. (OK, I'm sarcastic, but I think the physicists have to be a bit clearer in proving that their whizbang devices are not spatially complex...and yes, I am reading the papers to try to clear this up).
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
Yes, they seem to be ignoring spatial complexity here. That was my reaction to the quantum paper on the same thing.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
Yes, I think the field is incredibly strange and wonderful, but not for the physics. The ignorance and mutual misdirection are entertaining. What other field has physicists, philosophers, and computer scientists, all misunderstanding each other in fundamental ways? Now we have the optics community involved. Maybe at least we can separate the wave mechanics from the rest of it all, if there is any remainder.
I'm not trying to start a flamewar, but the claim that QM implies nondeterminism also falls into the unfounded hyperbole category. As someone wrote in Physical Review Letters a while ago, the stuff about trajectories not existing, and instantaneous quantum jumps, many worlds, etc., is a good way to keep from presuming too much information about a system, but it's not a proof of any deeper reality.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
I'm about at the same stage of understanding. I suspect that wave mechanics (as the opticists used) may underly a lot of the claims. QC relies heavily on Bennett's work in reversible computing. The idea is that information, and its underlying physical representation, can flow both ways through the logic gates, just as light can propagate or resonate both ways in an optical system. If the system is stable (that's something I'm not convinced of), then the observed wave function should reflect the proper relationship between the "input" and "output" (even if we, say, put in a known output and want to reverse to an input). Measurements against such a system should yield statistics that reflect the wavefunction at different parts of the system, and the wavefunction will represent something about the information we're seeking.
I don't see anything so mysterious about this. QM brings on a lot of handwaving (eg Deutsch's claim that QC "proves" that the many-worlds interpretation is correct), but I believe the opticists are on the right track when they say a lot of the logic can be done in non-quantum systems. QM at best provides a good source of waveforms to put through our interferometers.
---- "If we have to go on with these damned quantum jumps, then I'm sorry that I ever got involved" - Erwin Schrodinger
I did, but not nearly as much as this guy. I still have them Little Black Books to prove it, too!
**>>BELCH
Did anyone ever seriously play Traveller ? If so, what was the key to getting it to work ?
I bought the rules and thought it was a pile of poo. The individual combat system was awful and it didn't seem to have the aura of fun that say D&D had.
Donte Alistair Anderson Roberts - hi son!
Karma: Chameleon
I believe I still have the boxed set too, but only god knows why!!
Are they worth anything ?
Donte Alistair Anderson Roberts - hi son!
Karma: Chameleon
No one has ever shown that quantum computers could break a symmetric encryption at more than twice as fast as brute force, and the actual clocking of quantum gates is not that fast.
What everyone is talking about with encryption is Public Key, where quantum mechanics may be able to reduce the brute force test to n operations given an n bit key, and n quantum gates. This is particularly true of those built on prime numbers.
Interference *is* superposition (of out of phase waves). BTW: What quantum features of the light are they using exactly? Seems like the classical wave model to me. Acousic-optic transducers are used here (UT-Austin) as beam benders without so much hooplaah.
When I was able to do my own spam-armoring, you got a chance to email me. Now you can only hope I see your reply.
...both of which are elements in "quantum computing".
Cretin - a powerful and flexible CD reencoder
But if you can get results from a quantum computer without turning on the power, the off-quantum-computer should be more resistant to radiation than any other type of computer. You do need to give the computer time to not run, but a wind-up clock is rather resistant to radiation.
because its difficult to manipulate light in a conventional machine. we dont have fully optical switches yet commercially let alone a massively parallel optical processor. yes, its been known for a loong time since optical fibres carry multiple wavelengths of light and the human brain mimicks this with its massively parallel neurons but its not yet viable for commercial use -- the NSA might use it but most conventional machines cant be mass produced with it.
While this does sound very neat and seems like a fantastic idea, it does seem to have a few inherent limitations.
In order for this light interference method to work most efficiently, a single beam of light must be able to shine on the entire database at once. For small databases, no problem, but for large ones it seems an impossibility. Why not just do part of the database at a time? Well then you lose the reason you were doing this for in the first place, which is to make a single request to the database and come up with your answer.
Another limitation with the size of the database is the number of frequencies that the light must be split up into. I'm not sure of the actual number of frequencies that we know how to split light into, but there must be some limit. Potentially, with quantum computers, there would be no limitations. Just add more qubits.
So while this does sound very cool, I don't see it replacing quantum computers as the next big leap in computing.
---- El diablo esta en mis pantalones! Mire, mire!
you're thinking that an increase in speed of merely a billion times (or ANY physically possible multiplier) is going to help you brute force 256 bit keys?
</flame>
I suggest you go check up on the properties of exponents. A billion times faster is the same as reducing the keyspace by 30 bits: leaving you with a task equivalent to bruteforcing a 226 bit key on current hardware. If you make it a billion billion times faster, I need merely add 60 bits to my key to regain the previous level of security.
The thing about quantuum computers is that they are good at reducing the order of complexity of certain computations -- in this case factorisation. You only need to start worrying about symmetric keys when a quantum computer can solve NP problems in P time. But then you REALLY have to start worrying, because ALL symmetric ciphers are in NP.
Not possible. If all the energy of a supernova could be channeled into a ideal computer that did nothing but count, it would only get up to 2^219. (from Applied Cryptography by Bruce Schneier). Brute force attacks will never work against keys of sufficient length; you will need to find a weakness in the cryptographic algorithm (or find the sticky note the user wrote his password on, which is a much better bet).
How to solve most of our problems: 1.Lots of nuclear plants. 2.Cure aging.
Photons are pretty stable against these kinds of interference, since they don't interact strongly with matter. So, as long as you use high quality optical elements, you can do quantum computation experements at room temperature. Unfortunately, the lack of interactions makes it hard to implement quantum gates, making systems larger than 2 qubits difficult.
NMR quantum computer experements are also at room temperature, but have their own problems.
No, with this sort of device you do not have to iterate over the frequencies. If the 'on' bits of the modulator retard the light passing through them by, 2n-1/1 wavelengths and the off bits have no effect then when the beam is recombined you can just bounce it of a grating/prism into a linear array of detectors and there's your answer. The slow bit is reading the detectors, ie. as usual its the optical->electronic bit thats slow.
This sounds more like holographic computing, rather than quantum computing. In QC, a search would involve manipulating the system until one state is left. In this article's example, you still have to iterate over the frequencies to find the frequency that changed. As I am given to understand QC, were this a true analog to QC you'd simple have one color standing alone, with no searching.
www.eFax.com are spammers
Agreed. I have no points left :(
Really? I would have thought the transducers to be higher than 20khz. And when the jeep drives by, its really only the longest wavelengths that you hear.
"except it runs on light at similar speeds" - don't you mean wavelengths?? Isn't that whole speed of light declared as a constant and not a variable or a pointer??
Wheeeee
I suppose a unit of quantum speed could be how long your average gate operation takes. In an ion trap QC it's about 10^-3 s. Or a clock speed of 1 milliHertz. Crap, in other word.
:wq
If you didn't get basic atomic structure in grade school you should just be taken out and shot.
They pretty much glossed over any details. I'll wait for the article in Nature.
I'm trying to teach myself to set people on fire with my mind... Is it hot in here?
...me without mod points. Ah well.
TomatoMan
-- http://frobnosticate.com
But you don't have to look at the whole bunch of them individually. And regardless, you don't have to look at them at all. They are sorted, which was the goal.
-no broken link
There are 7-qbit quantum computers.
-no broken link
Another example is finding the bounding convex polygon for a set of n points. I don't remember the runtime for the algorithm, but for the real world it's O(n): you get a board, nail in the n points, then find a rubber band and wrapp it around the nails.
The article describes another one of these problems that is solved faster with a physical process, in this case looking up a record in a database. By physically encoding data differently, you can find a record in a large set in a single step (well, maybe not since you still have to FFT the light to find the frequency, so I'm still not sure how this is faster than the O(log n) of an index, remember FFT is also O(log n) where n is the number of frequencies, and you need the number of frequencies to be the same as the number of records so it seems equivelent to me, but there may be some other way of determining the frequency of the altered light).
This can't be used to crack RSA, and it's not a general method of algorithmically running through a large number of possiblilities concurrently, which we get with quantum computers. There may be a way to crack RSA generically with a physical process (didn't Shamir come up with an optical process for 512 bit RSA). But this has nothing to do with that.
-no broken link
Egan's homepage can be found at http://www.netspace.net.au/~gregegan/.
Lawrence Person (lawrencepersonh@gmailh.com (remove all "h"s to mail)
http://www.lawrenceperson.com/
"If the database in question were the Manhattan phone book, the search for a single phone number could take a conventional computer several million searches, while a light-based device could pinpoint the number in just one."
The operations it takes to search through a million-entry sorted database isn't a million. It's proportional to log2(n). Think about it. Divide it in half. Is the current entry bigger or smaller? Bigger->Divide the bottom half in half and repeat. Smaller->Divide the top half in half and repeat.
So how many times can you divide a phone book in half before you're guaranteed to find your answer? log2(n).
Exactly! But since there are no gates which have been realized *physicaly* outside of a few prototypes, there is no known speed yet.
-david
That article was insipid to the point where I couldn't finish it. A few points in the first few paragraphs are worth mentioning:
1) Quantum speeds? WTF is that? There's no such unit, not even associated with quantum computing.
2) The device "mimics quantum interference". No, it's light; it displays quantum interference. Light is photons, quantum particles. Dur.
3) "performs some tasks a billion times faster". This is what I call a 'crazy number' since it's not based on any sort of measurement and thrown in only for show-value.
Don't get me wrong, I'm active in QC research and I like what the folks at Rochester are doing, so, too, the folks in an optics group at Los Alamos. But whoever wrote that Science Daily article is whacked out. It cheapens everything.
So, it looks like this thing can do computations about a billion times faster then conventional methods....that's gotta knock a hole in current key lengths and security...I wonder how fast this thing has to get before brute forcing a 256 bit key becomes feasible. (big math people out there anywhere?)
Fortunately, that should also offer a slew of new possibilities for encryption schemes that were previously too slow or bulky.
On your mark, get set, encrypt
----------
ah honey, we're all resplendent - Bill Mallonee
In our real spacetime, you probably won't get radiation resistance. Quantum effects are all extremely susceptible to any sort of interference. AFAIK, any sort of quantum computing device only works as close to absoulte zero temperature as you can get.
what does this do to all the companies spending *billions* on quantum research? does this mean they are screwed? or does this mean they accelerate their research? i hope for the latter... (not just because i work for one, i assure you...)
The REAL sam_at_caveman_dot_org is user ID 13833.
The term debugging originated supposedly when they found a bug in between the relais of one of the first computers. I was just thinking what would happen if they actually build one of these machines and had to debug it: would they find a firefly??
Disclaimer/shameless plug: I've recently compiled a semi-technical paper on some of the theory behind quantum computing, as a project in our undergraduate physics course.
--
Escher was the first MC and Giger invented the HR department.
Oh come on people if this isn't +5 informative then Eric Raymond isn't ugly
'There is a Light that never goes out.'
In analysing this sort of thing, the "size" of the problem is usually taken as the logarithm of the number of entries (ie the number of bits required to label each item). Since the strength of the output beam decreases linearly with the number of entries, it falls off exponentially with problem size.
Now, it can be shown that even with a Quantum Computer, the best we can do is to speed up the search by the square root of the number of entries. So 10^6 entries takes 10^3 searches, and so on. This isn't an exponential speedup (which is impossible for Unordered Search), but I can't see that this "light interference" method could match a quantum machine.
And it certainly couldn't match the exponential speedups on Factoring, the killer app for Quantum Computing.
StuP
This would be the perfect computer to crack open when you're drunk/stoned/whatever. "Wow, look at the pretty colors....wooowww...."
The Blaster Master Fighting for Truth, Justice, and Evil Pie since 1979
To search the database, Walmsley directs a beam of light toward the modulator. The light is first split into two, with one part traveling through a prism so that a rainbow of different frequencies of light shines on the modulator. Each frequency shines through a different compressed or expanded part of the tellurium dioxide, which bends that frequency of light the way a straw appears bent when sticking out of a glass of water. The rainbow of frequencies is then recombined into a single beam. By mixing the new beam with the original beam that entered the device, a single frequency will emerge as having been altered by its trip through the database.
Doesn't the beam of light have to contain the data that the user is looking for so that the match can be made? How is the data encoded into the light and how much data can be encoded? Guess I need more info. It kinda strikes me that all that guy is doing is using the 2d method of storage and the availability of air as a transmission medium for light to establish a connection to EACH section of the data storage medium. What's that got to do with quantum computing.
Urgh. I'm feeling rather confused today.
Pinky: "What are we going to do tomorrow night Brain?"
Pinky: "What are we going to do tomorrow night Brain?"
Brain: "I would tell you Pinky but this 120 char limi
So you manage to prove that data retrieval using light is viable but how viable is the storage medium? It won't be any good having a brilliant information retrieval tool if you loose the data every time you have to reboot or if the storage medium requires 1 square cm per bit.
Pinky: "What are we going to do tomorrow night Brain?"
Pinky: "What are we going to do tomorrow night Brain?"
Brain: "I would tell you Pinky but this 120 char limi
My seventh grade social studies teacher showed us punched cards with the holes along the edges. You ran a long metal pin through the holes and lifted, and the cards where the edge was punched away stayed in the tray. Repeat for multiple WHERE clauses. At least that could handle multiple cards with the same value.
"If the database in question were the Manhattan phone book, the search for a single phone number could take a conventional computer several million searches, while a light-based device could pinpoint the number in just one"
Unless you use a database of course...
Will code a sig generator for food
Anyone ever spend the extra mega-credits to get a fiber optic based computer for their starship?
Though in Traveller, you didn't get better performance, you just got radiation resistance.
Well there is a bit of a difficulty in explaining exactly where the computational power of a quantum computer comes from. Kind of like asking where the power of a classical computer comes from (and don't say "from the power company" damnit (yes, I'm from California)).
But the "power" of quantum algorithms over classical algorithms makes itself clear when you realize that all efficient quantum algorithms make use of a COLLECTION of quantum systems. When you take the polarization of a single photon and use polarization filters you essentially have a single quantum bit of information corresponding to the two polarizations. But in order to make a quantum algorithm, you need to put a bunch of these qubits together and they must interact in a non-trivial manner. Thus you need to get someway for the polarization of one photon to interaction with the polarization of another photon. This is really a pain in the ass to do without destroying the photon or the coherence of the polarizations.
So I guess what I am saying is that when you take a bunch of quantum systems and build a quantum algorithm, the power of the algorithm comes from the dynamics of the interaction of multiple quantum systems.
The fact that quantum computers are probabilistic and rely have a "collapse" of the wavefunction at the end of the computation are sort of secondary to the issue of where the power comes from.
dabacon
As has been pointed out by many posters already, this is not what nearly all researchers would call a quantum computer. A universal quantum computer, from a physicists perspective, is a computer built with pieces which obey quantum mechanics AND can be used to EFFICIENTLY simulate the effects of systems obeying quantum mechanics. This EFFICIENCY condition is extremely important, because, for instance, your classical computer can simulate quantum physics...it just takes it a hell of a long time for most reasonably sized problems!
The device described (poorly) in the article fails to achieve an efficient simulation of quantum systems because the number of frequencies needed in order to perform a given simulation will scale exponentially in the size of the quantum computer being simulated. Albeit technologically interesting, the computation performed by the experiment is not something which a classical computer cannot do as efficiently.
But what really troubles me is the quote attributed to Walmsley in the article:
"We wanted to show that the implementations which have been done with quantum computing have an exact analogy that is just as effective in light-based processes," says Walmsley.
Just as effective?! That is a just not true. Is this a case of a scientist being quoted out of context or is it a case of a scientist who doesn't understand the issue?
Yes, MTIOQC (my thesis is on quantum computing), so I feel like I have a little bit vested in this issue. Being so biased, I hope that this is just an out of context mistake.
I would like to think that our enlightment grows with time, but every new article I read about quantum computing research seems to be filled with more and more hyperbole (oh do I hate the words "paradigm shift" and "synergy") and less and less good science. Don't get me wrong, I think quantum computing has a promising future both in actual future practice as well as in helping shed light on areas of physics (We all learned that quantum mechanics destroyed the computer-like determinism of Newtonian mechanics, but now we think that, while the universe is not a big classical computer, the universe may be a big quantum computer!), but irresponsible press releases drive me bonkers.
dabacon
This is definitely not scalable. They claim it runs at "Quantum speeds" which isn't even really a word. There is no such thing as "Quantum speed", a quantum computer can take just as long for any particular algorithm as a classical computer, the special thing about QC is just that the speed scales polynomially with input size rather than exponentially. This is *not* true of the light interference system they describe, for many reasons some of which have been pointed out here already. (The time it takes to iterate through the outputs, the size of the beam, the number of beam splitters you would need, and the limited bandwidth of the light spectrum). None of these things scale polynomially with the input size so claiming that this is a substitute for Qc is nothing more than a trick to get funding. Plus, the idea isn't exactly new. I attended a conference on Quantum Computing at Georiga Tech over a year and a half ago where we discussed this very idea, and all parties (many PhD CS and Quantum Physicists among us) agreed that it could not yield the power of a quantum computer.
Yes but quantum computing Sounds So Much Cooler....
In all seriousness, this is the sort of situation where the Internet is more a hinderence than a help. Over time discussions such as this will polarize the lay community either for or against a particular area of research, wher two areas of research strive to achieve similar goals.
Public Opinion greatly influences funding of research, so I hope that premature dabates of which technology is superior, won't shape decisions to fund one or the other, since ther is the possibility that one or the other area of research might hit a brick wall at some time in the future, at which point it wll be nessecery to pursue the other area of study. It would be bennefitial to all to have continued both areas of research in parrelel.
Don't get me wrong. I don't believe that discussions like this alone will influence the course of research, but merely that the colaborative enviroment the Internet offers will promote (suprisingly) colaboration to the point where only one research path will be pursued by both teams, working together, rather than competing, as it were.This is an area whewre competition is a positive thing in academic research. I merely question the degree to which the Internet actually contributes to this.
--CTH
--
--Got Lists? | Top 95 Star Wars Line
So in the case of Walmsley's device, 50 different frequencies of light shine through the modulator, and if the 20th frequency is the altered one, then Walmsley knows that the bit of information he was searching for is located at position 20 in the database. A conventional computer would have had to check 20 times to find the location. It sounds all so simple that I can't help but ask : why nobody ever thought of it?
There's always sufficient, but not always at the right place nor for the right folks.
In my yoga class, there's a guy who lives on prana (air) and light. This strikes me as remarkably similar to that philosophically. It's the coolest thing I've heard in a long time.
Francine Hardaway, Ph.D. "It's not what happens to you; it's how you come to it." http://www.stealthmode.com
So we convert the problem from scanning a spatial array to scanning a frequency array. Don't we still have to analyze the frequencies to figure out which one has been altered?
I suppose that each frequency could go to a parallel detection array, which would then drive some sort of interrupt, however this would seem to become unwieldy as the problem space increases.
Can someone explain further just how the detection of which frequency of light was changed would actually work in practice with a large problem space?
In case you haven't noticed, there is a [so-called] Ten Year Gap in the levels of technology that the military and government R&D comes up with, and what hits the store shelves for us to buy. We get the R&D hand-me-downs that they're unthreatened to release, as well as odds and ends that they never had any real use for in the first place. That means No Such Agency and most of the rest of the alphabet gestapo have at least ten years on us in tech level when it comes to cryptography. Personally, I'm inclined to think of the disparity as a curve. If they can do ten years, they can do twenty or a hundred years. All they have to do is set the pace of R&D release just slightly slower than the rate at which they innovate, and there's a gradually widening chasm of tech levels. And lest we forget, civillian technology is cancellable at a stroke using electromagnetic pulse should they consider it warranted. Reminiscent of Zelazny's Lord of Light.
The recombinant beam isn't compared to the original beam. When you recombine the two beams you create interference. Depending on how you set it up, the interference could be constructive or destructive for the target or background frequencies. In other words, you can rig it so that only the correct frequency will make it through, and either a)detect frequency directly to determine which value is correct or b)use a prism to spread the beam again and project it against a wide detector and see which frequencies are appearing/not appearing, and thus which is correct.
While this is a neat trick, it isn't readily scalable and thus will be of limited use compared to a quantum computer. It is working in parallel, but with only 50 values. You could expand that number by using multiple units, but based on the capabilities quoted in the article the system can only be scaled linearly, while a quantum computer can scale exponentially.
Now if the can/do have a way to use those 50+ bits exponentially, that's a whole other story. All of this depends on how the data is stored within the tellurium dioxide and thus how it affects the light traveling through it representing the database. Although the method indicated is a linear search the article seems to indicate that it has much more potential.
In any case, either the article overstated things or did not report the technique correctly.
cryptochrome
---If you can't trust a nerd, who can you trust?
The following was in response to a question similar to my previous statement, which I received very promptly from Iam Walmsley:
You are correct in the statement that the scalability of our experiment is no better than that of a classical system. (I don't think the UR News Release claimed otherwise, did it? If so, I'd better check with our PR people!) The point is really a different one:
First, we have shown formally that any information processing system based on quantum interference alone (e.g. a single Rydberg atom, or a single photon) can be implemented with equal efficiency with an all-optical interferometer. The important physics here is to realize that with a quantum computer the information in the register has no reality until you read it out, and so you must account for the readout resources in determining the efficiency of the computer.
Second, we implemented an all optical version of Bucksbaum's Rydberg atom Grover search to show that our hypothesis is correct. The resource scaling in both is slightly better than that of Grover's second search algorithm, since we do not need the inversion-about-the-mean operation he proposed. Instead, we use part of the input as a reference beam and make use of interference to do the phase-to-amplitude conversion.
This might leave one with the impression that all interference based schemes, including those based on quantum interference alone, can never do better than a classical machine. But recent articles by D. Meyer (PRL, 2000) and E. Knill et al (Nature, 2001) show that interference without entanglement can be used to advantage over classical computers. Therefore we are now seeking to implement the algorithms they analyze optically, and to provide a measure for evaluating the resources needed for them.
Hope this helps - rest assured we are certainly not claiming that we can do everything full-blown quantum computers can, only those that are based on single-particle interference alone.
Parenthetically, one can look for a single marked element in a database of 2^50 items using our method quite easily, provided the database is binary encoded to begin with. But such encoding schemes are also available in classical machines. For unary encoding we are limited to 50-element databases. Perhaps this is what you meant in your second paragraph.
Best regards
IAW
---If you can't trust a nerd, who can you trust?
So far we have 3 people posting who claim to be doing Quantum Computing research. No wonder we're not getting any closer to getting a QC built.. all the researchers are posting on slashdot all day.
According to the article, or at least to my limited understanding of it, each 'record' needs to be represented simultaneously on 'modulator.' Wouldn't this then cause a restriction on the size of your computer, based on the size of the modulator?
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
*smirks*
Let's look at the story for a second here folks.
The scientist set up a data-storage device (in this case an acoustically massaged medium), then an information retrieval was carried out against the medium. This retrieval was carried out in parallel. Now this is fairly exciting news, but it has some serious distance to go before it manages to become something general enough to threaten the intellectual-share of true quantum-entaglement computing schemes.
The promises for the device so far seem to be in determining data returns along mulitple paths. In effect, the thing is performing the many many calculations (in this case actually only data-retrievals). However, it's performing them in parallel.
In addition, I'm curious as to how the data is retrieved. If the recombinant beam must be compared to the original beam along all the frequency divisions, there's another indivisible operation requiring some length of time.
But....
It is an interesting method of encoding/decoding data from a medium to a laser without transducers. I'd say that this technology has great promise as a method to be derived from to create all-optical switching fabrics that are actually data-sensitive (how'd you love it if you could decode, process, and filter packet data from the very laser transmission that carried it down the fat fiber pipe...?)
Nietzsche on Diku:
sn; at god ba g
:Backstab >KILLS< god.
actual digital information through binary
code? Electricity runnning through
circuits. What is one way to get
electricity? Light. There, it's as simple
as that. I even made a formula for you guys:
Light = Electricity = Binary Circuits = Digital Data.
somebody once asked / 'could I spare some change for gas / I need to get my self away from this place' / I said 'Yep. What a concept. I could use a little fuel my self and we could all use a little change
-All Star, Smash MOuth
You should state it as : I can't see THE LIGHT (would be faster than audio or even RF but what is actually new here?). But I think you're absolutely right about all the rest.
Don't mind this dude, half of the time he goes half naked, and that's not the same as full time quarter naked, is it ??