Breakthrough Toward Quantum Computing

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Breakthrough Toward Quantum Computing

Posted by Soulskill on Monday July 18, 2011 @07:59AM from the advancing-in-fundamental-increments dept.

redwolfe7707 writes "Qubit registers have been a hard thing to construct; this looks to be a substantial advance in the multiple entanglements required for their use. Quoting: 'Olivier Pfister, a professor of physics in the University of Virginia's College of Arts & Sciences, has just published findings in the journal Physical Review Letters demonstrating a breakthrough in the creation of massive numbers of entangled qubits, more precisely a multilevel variant thereof called Qmodes. ... Pfister and researchers in his lab used sophisticated lasers to engineer 15 groups of four entangled Qmodes each, for a total of 60 measurable Qmodes, the most ever created. They believe they may have created as many as 150 groups, or 600 Qmodes, but could measure only 60 with the techniques they used.'" In related news, research published in the New Journal of Physics (abstract) shows "how quantum and classical data can be interlaced in a real-world fiber optics network, taking a step toward distributing quantum information to the home, and with it a quantum internet."

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*stare* by Spigot+the+Bear · 2011-07-18 08:10 · Score: 1

Right, magic, got it.
How do they work? by Normal+Dan · 2011-07-18 08:14 · Score: 2

How would one read the output of a quantum computer if they quantum state changes upon observation? Wouldn't it just spit out random numbers?

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1. Re:How do they work? by Anonymous Coward · 2011-07-18 08:22 · Score: 1
  
  Wouldn't it just spit out random numbers?
  Typically, yes, but this can be more useful than it sounds! What you want to do is perform a number of quantum operations such that, when you do measure your qubit, you will get the answer you want with probability >0.5. The operations you can perform on a qubit are very limited (you'll notice there are no AND operations, OR operations or anything that would allow you an IF statement) and you almost never get answer that's correct with absolute certainty, but they could still be fantastically useful. With just a few operations you can sometimes coerce a qubit into a state such that it will give you correct answer with probability between 0.5 and 1.0. Once you have that, it's just a matter of repeating the computation enough times to be confident.
2. Re:How do they work? by vlm · 2011-07-18 08:32 · Score: 2
  
  How would one read the output of a quantum computer if they quantum state changes upon observation? Wouldn't it just spit out random numbers?
  One term to google for is decoherence.
  The two paragraph wikipedia answer is at:
  http://en.wikipedia.org/wiki/Quantum_computer#Operation
  The multi-page answer at quantiki is at:
  http://www.quantiki.org/wiki/Basic_concepts_in_quantum_computation#Decoherence_and_recoherence
  My crappy slashdot car analogy is the internal state of my car is almost infinitely complicated, O2 sensor levels and thermostat bypass fractions. But you could theoretically compute an algebraic equation that boils down to can I drive 400 miles on a tank of gas? The answer at the end is, is the engine running or not, just one binary bit. All the hidden internal variables and states, zillions of them, like coolant temp, O2 loop state, etc, all collapse down to one bit. Its not really important what the internal state is when the engine shuts off, or if it shut off because the O2 loop leaned out of spec, or the fuel pump control loop when haywire when it sucked air, or...
  So, a 1024 qubit computer has 2^1024 internal variables all of a vaguely analog complex number value, and those 2^1024 values collapse down to a mere 1024 bits when you factor my RSA key... There's a darn near infinite number of possible values that collapse down to 1024 bits and you randomly get one of them.
  
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3. Re:How do they work? by Alsee · 2011-07-18 11:16 · Score: 3, Informative
  
  We can compare it to rolling dice, where the dice can be loaded to shift the percentages. If we put a weight on the 1, we might roll a 1 half the time and randomly get 2 through 6 the rest of the time. In quantum mechanics we can preform calculations that change how the dice are loaded. Ideally, we can load the die so strongly that 2 through 6 are driven down to zero percent, and 100% of the time we "randomly" roll a 1.
  Depending on the particular problem and the particular technology used, certain parts of the computer might not be working with a perfect-clean 100%. Particular parts of the computer might have the dice loaded to 99.9% randomly roll a particular result. Obviously we don't want a computer that's oly 99.9% right :D
  Different kinds of quantum computers deal with that in different ways. The simplest example is a quantum computer that works on a beam of photons or something. A beam of light might contain a trillion photons per nanosecond. If 99.9% of those photons randomly come out on the right answer, the right answer obviously lights up brightly. The 0.1% of photons lighting up the various wrong answers will be too dim to notice.
  For some quantum calculations they use the very simple technique of just running it a dozen times or something. There's basically a 99% chance you'll get a dozen matching correct answers, and a 1% chance you'll get eleven matching correct answers and one random error that you throw away. There is a minuscule chance you'll get (and throw away) two or possibly three garbage results out of the dozen, but the only way you would ever get a wrong answer from that is if the same wrong answer came up seven or more times at once, and mathematically that won't happen a million or billion years.
  However for a "real" desktop-type quantum computer, there's a much more complicated and powerful technique they would build in.... error correcting bits and error correcting codes. By adding in a few extra bits, the computer can automatically spot and correct any random wrong values as soon as the appear. All of the automatic error correction stuff might make the computer something like 50% bigger or maybe twice the size, but it can easily match the (effectively zero) error rate of standard computers.
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4. Re:How do they work? by mgiuca · 2011-07-24 17:44 · Score: 1
  
  Couldn't you also use a regular computer to verify it with 100% accuracy (for some classes of problems)?
  For example, I can (as I understand it) use a quantum computer to find the two prime factors of a semiprime number. Say that the QC can give me the correct answer with, say, 60% accuracy. Now I just need to take the answer and use a regular computer to multiply the two numbers and see if they give me the original number. If they don't, I ask the QC again until it gets it right. No need to continuously run the computation to reduce the probability of error. Is there some reason this might not work?
5. Re:How do they work? by Alsee · 2011-07-25 21:02 · Score: 1
  
  Yes, for most kinds of problems a normal computer can quickly verify whether a quantum result is correct. However I don't think a normal computer can verify certain kinds of "non-existence" or "optimum" results. For example if you plug in a problem and the quantum computer says no solution exists, a normal computer can't confirm that. Or if you plug in a traveling salesman problem asking for the shortest route and it gives you a short-route answer, a normal computer can obviously calculate the length of that route, but the normal computer generally can't verify that no shorter route exists.
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6. Re:How do they work? by mgiuca · 2011-07-26 01:04 · Score: 1
  
  Thanks! Very informative. And ... Slashdot requires that I say more than just this. Hmm. Extremely informative?
Re:Quantum Internet? by clyde_cadiddlehopper · 2011-07-18 08:15 · Score: 1, Funny

Cue Schrodinger's Goatse in 3-2-1...

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Re:Quantum Internet? by Anonymous Coward · 2011-07-18 08:18 · Score: 2, Funny

Quantum porn?
He or She does all possible things with another He or She all at once. If you really like what you see, don't blink because it will be something different by the time your eyelids open back up.
Re:Quantum Internet? by vlm · 2011-07-18 08:19 · Score: 1

Quantum internet, really? Will I be eating Quantum pop tarts while I surf Quantum porn?
It will almost certainly be the marketing term of the decade.
Much as I had "turbo sunglasses" in the 80s, because nothing says glare reduction than an turbocharger, and I bought a nano "i-pod" some years ago, i- as in internet when ironically its probably the only piece of consumer end-user electronics apple sold that decade without a web browser.
I'm sure I'll see stickers to put on my quantum computer that somehow make it faster, and quantum tennis shoes, RSN.

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um... by Charliemopps · 2011-07-18 08:19 · Score: 1

Someone clarify this for me: I thought that currently we could only entangle photons, and the photon entanglement could be explained by classical optics physics. So while it's "technically" entanglement, it's not what we are really after. Do we need to entangle non-photon particles or will photons be good enough?
1. Re:um... by jmizrahi · 2011-07-18 10:08 · Score: 5, Informative
  
  Neither statement is true. First, we have entangled many systems other than photons. We have entangled trapped ions, neutral Rydberg atoms, superconducting qubits, nuclear spin states, and the list goes on. There are advantages and disadvantages to each quantum computing architecture. One of the fundamental issues facing all quantum computing architectures is the question of scalability. It is not always clear how to go from 1 or 2 qubits to thousands or millions of qubits. Some architectures, such as trapped ions, lend themselves naturally to scaling. The significance of this work is that up to this point, it has been unclear how you might scale a photonic quantum computer. The authors of this paper have taken the first steps towards overcoming that obstacle. As to your second statement, observed photon entanglement cannot be explained via classical optics. It has been shown to violate a Bell inequality, which is the hallmark of non-classicality in quantum mechanics.
Re:First Quantum Post by blair1q · 2011-07-18 08:21 · Score: 1

But not if they actually try to read it.
imagine a beowulf makerbot.. by decora · 2011-07-18 08:24 · Score: 1

of these things...
Price Pfister? by nog_lorp · 2011-07-18 08:25 · Score: 1

I hear Price Pfister is releasing a breakthrough new design in Commodes, called the Qmode!
Re:Quantum Internet? by ThePeices · 2011-07-18 08:29 · Score: 1

"Quantum internet, really? Will I be eating Quantum pop tarts while I surf Quantum porn?"
No, you will not be going down on slutty pop music singers while looking at porn on a quantum computer.
You are just not an A-list celebrity.
am I the only one ? by Chuby007 · 2011-07-18 08:30 · Score: 1

am I the only one that has no idea of what that post means ? don't lie !
Re:First Quantum Post by Schmorgluck · 2011-07-18 08:41 · Score: 1

Actually, since you couldn't know for certain that your post would be first before you had posted it, it was in a quantum state of being first and not-first until you collapsed its wave function by posting it.
Or something like that...

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Re:Quantum Internet? by equex · 2011-07-18 08:48 · Score: 1

Haha! Why AC? This is a good joke!

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Level 60!?! by Kamiza+Ikioi · 2011-07-18 09:02 · Score: 1

I never got past level 3 in Q-bert! First Pacman, then Donkey Kong, now Q-bert. This is getting serious.

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Re:Fucking Qubits... by maxwell+demon · 2011-07-18 09:16 · Score: 1

You don't want your qubits to fuck. When they fuck, they don't work.
But maybe that's why we have so much trouble with getting more qubits. If we let them fuck, maybe they'll multiply by themselves!

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Re:Quantum Internet? by mrops · 2011-07-18 09:26 · Score: 1

You wouldn't know if its a porn or a preacher giving a sermon until you hit play, and then as soon as you observe it, it won't be either.
Re:Quantum Internet? by Dogtanian · 2011-07-18 10:32 · Score: 1

Quantum porn?
He or She does all possible things with another He or She all at once. If you really like what you see, don't blink because it will be something different by the time your eyelids open back up.
You mean like a pornographic version of that Doctor Who episode with the scary statues?

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Re:Obligatory: But Will It Ecrypt My Google Mail by peragrin · 2011-07-18 10:34 · Score: 1

Sure but china has already hacked your password anyway so there isn't much point.

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Re:Quantum Internet? by Dogtanian · 2011-07-18 11:00 · Score: 1

I bought a nano "i-pod" some years ago, i- as in internet when ironically its probably the only piece of consumer end-user electronics apple sold that decade without a web browser.
Sure, but remember the "i" prefix originated (as far as Apple were concerned) with the original iMac, not the iPad. The former was Apple's "comeback" product and culturally prominent at the time (remember the late-90s translucent coloured plastic fad it sparked). In that case it *did* supposedly stand for "Internet".

I'm assuming that the name "iPod" was then chosen to piggyback on the success and name recognition of the iMac, regardless of whether the "i" was relevant. The fact that the iPod was even more successful than the iMac makes it easy to forget that it didn't originate Apple's iNaming scheme(!)

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Re:Quantum Internet? by Alsee · 2011-07-18 11:25 · Score: 1

Quantum link to goatse... you don't know if you saw it or not, but you're absolutely certain that you don't want to know.
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Re:Quantum Internet? by Greyfox · 2011-07-18 11:36 · Score: 1

Hmm. Looks like a wormhole...

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Re:Quantum Internet? by Lanteran · 2011-07-18 12:12 · Score: 1

You won't know if this link is goatse until you click it and collapse the wave function!

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this is not a breakthrough... by Gravis+Zero · 2011-07-18 12:19 · Score: 1

it's a quantum leap. :)

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Re:Quantum Internet? by tsotha · 2011-07-18 12:59 · Score: 1

You will be surfing porn an /. at the same time. And, probably, eating both chocolate and strawberry pop tarts.
Hey... by tsotha · 2011-07-18 13:00 · Score: 1

How many of these "breakthroughs" are going to have to happen before I can actually buy something. It's like a breakthrough and not a breakthrough at the same time.
1. Re:Hey... by Sulphur · 2011-07-18 20:06 · Score: 1
  
  How many of these "breakthroughs" are going to have to happen before I can actually buy something. It's like a breakthrough and not a breakthrough at the same time.
  As soon as they get 640k qbits. No one will ever need more than that.
Quantum mechanics is... by jamiesan · 2011-07-18 14:20 · Score: 1

Just the universe's way of waffling Schrodinger: Are you being wishy washy? Universe: Well... yes and no.
Re:Quantum Internet? by Thing+1 · 2011-07-18 14:50 · Score: 1

Hmm. Looks like a wormhole...
What, Morgan Freeman's?

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Re:I'll believe it when I see it. by Wandering+Idiot · 2011-07-18 16:34 · Score: 1

I don't suppose you'd care to elaborate on what your brilliantly simple Theory of Everything involves, would you? (Presumably not, since it's much easier to just imply you have one and act smug, rather than proposing a theory and running the risk of actual criticism)
Que the Sam Beckett jokes by PDX · 2011-07-18 17:05 · Score: 1

If the wmap cold spot is an alternate universe then a tachyon beam might be able to break past dimensional barriers that exist between universes. If the other universe has two cold spots then a hub of data could be formed. Imagine the total output of every universes' data collections piped across dimensional barriers. The rate of data is limited by the phase data and the rotation of the beam. Multi-verse theory has proved correct. The downside is not knowing if anyone can survive in the other universe. The challenge is to detect FTL signals.
Re:Quantum Internet? by narcc · 2011-07-18 19:05 · Score: 1

In the before time, in the long long ago, we had tons of stuff prefixed with "e" or "i" -- how Apple managed its now near monopoly on that particular lower-case vowel prefix is anyone's guess.

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Re:Quantum Internet? by Sulphur · 2011-07-18 19:57 · Score: 1

In the before time, in the long long ago, we had tons of stuff prefixed with "e" or "i" -- how Apple managed its now near monopoly on that particular lower-case vowel prefix is anyone's guess.
Favorite letter?
LOL cats by jjbarrows · 2011-07-18 23:28 · Score: 1

Should be funny, not dead and/or alive, long live classic internet!
Will I get a quantum camera... by gestalt_n_pepper · 2011-07-19 00:31 · Score: 1

to see what might have been?

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Re:I'll believe it when I see it. by Maritz · 2011-07-19 05:23 · Score: 1

Physicists are headed in exactly the wrong direction with their current superstring theories and M-theory. If they would just let the math guide them, the solution would be obvious.
Please, elaborate. In detail. I wouldn't understand but it would be fun to try and ask someone who would understand to put it into thick bastard terms for me. You ought to drop a quick email to the likes of Brian Greene, Ed Witten etc if you get a minute.

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Bad description of entanglement by harryjohnston · 2011-07-19 17:58 · Score: 1

From TFA: "imagine that two people, each tossing a coin on their own and keeping a record of the results, compared this data after a few coin tosses and found that they always had identical outcomes, even though each result, heads or tails, would still occur randomly from one toss to the next". That's badly wrong. (Although I'm sure the researcher understands quantum mechanics, it was probably the PR guy who got it wrong!)
Entanglement really isn't all that mysterious; it just seems strange if you haven't gotten your head around non-commuting observables. Entangled particles are the quantum analogue of classical correlations - so it isn't as if two people are tossing separate coins, which of course aren't correlated.
Instead, imagine choosing a playing card at random from a shuffled deck and (without looking) cutting it in half and putting the two halves in separate envelopes. Keep one envelope and send the other to a friend living near Alpha Centauri. Open the envelopes at the same (pre-arranged) time. Gee whiz, you both simultaneously see two halves of the same card. Magic! (Well, maybe not.)
That's the classical playing card. A quantum playing card is weird: you can't see whether the card is black or red and whether it is odd or even at the same time. If you find out whether the card is black or red the number on the card changes at random; if you find out whether it is odd or even the suit of the card changes at random. Just to really make things awkward, you can choose to make a measurement that one third looks at the card's colour and two thirds looks at whether the card is odd or even (yes, I know that doesn't even make sense but that's the way it works). Then ... if you cut a whole bunch of cards in half, do different measurements each time, and take care of a few loopholes, you find that the statistics you get prove that until you looked at each card (or half of it) it didn't actually have a specific colour or a specific number, just a wavefunction describing the probabilities. This is called Bell's Inequality.
My advice: if you don't need to understand it, don't bother trying. The important point is that it's the quantum cards (non-commuting observables) that are weird, not the fact that you can cut them in half (entanglement).
(Incidentally, if the card has been cut into two, and you look at the colour of each half, the numbers on the two halves change independently of one another. The entangled cards aren't mystically bound together forever. Only the initial measurement is the same.)