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Data Storage Science Technology

Australian Researchers Demo Random Access Quantum Optical Memory 74

nuur writes "Researchers at the Australian National University have developed a new form of optical memory that allows random access to stored optical quantum information. Pulses of light are stored on a kind of 'optical conveyor-belt' that is controlled with a magnetic field. By manipulating the magnetic field, the conveyor-belt can be moved, allowing the recall of any part of the stored optical information. The research is published in Nature." You'll probably know after reading the abstract linked whether you'd be in the market to pay for the whole thing.
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Australian Researchers Demo Random Access Quantum Optical Memory

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  • All I know (Score:5, Funny)

    by Chuck Chunder ( 21021 ) on Thursday September 10, 2009 @09:46PM (#29385555) Homepage Journal

    You'll probably know after reading the abstract linked whether you'd be in the market to pay for the whole thing.

    All I know is that my head hurts.

  • Yeah, well (Score:5, Funny)

    by Anonymous Coward on Thursday September 10, 2009 @09:47PM (#29385565)

    For my storage requirements I need something more reliable than "random" access. Sheesh.

    • by bluelip ( 123578 )

      Hmmmm...... You run w/ no RAM?

    • I have random access to all of your data, one bit at a time. Here's a little example to prove it (sorry if this freaks you out):


      • by Sky Cry ( 872584 )
        Bullshit! All my data consists of 1s!
      • Of course there's a 0! I use base 1. All my data is 0s.
    • by Fred_A ( 10934 )

      For my storage requirements I need something more reliable than "random" access. Sheesh.

      Oh it's very reliable. You just don't know what your data will be until you read it.
      And then it's gone.

    • And no matter what you try to open it always opens your porn.
  • RAM?? (Score:5, Insightful)

    by bluelip ( 123578 ) on Thursday September 10, 2009 @09:50PM (#29385579) Homepage Journal

    Doesn't really sound like 'RAM". Sounds more like a tape storage device. The term 'RAM' was coined to indicate any spot in memory could be accessed in generally equal time. Tapes have to rewind, move.

    • Re: (Score:3, Interesting)

      by BikeHelmet ( 1437881 )

      But it could be fast enough that it doesn't matter. Perhaps someone that read the brief could chime in?

    • by potatog ( 996901 )

      RAM is not about O(1) read latency. Quantum information can be read only once, so _on-demand retrieval of arbitrary quantum states of light_ may prove useful in quantum computation.

      • by bluelip ( 123578 )

        Sounds like someone is about to drop out of CS and head towards a liberal arts degree.

        Read up on what RAM was/is and get back to us. It'll do you well to improve your HS Freshman midterm exams in basic CS theory.

      • It is (under physical constrains in out Universe, speed of light and such) is O(log(N)) in the best case (for N being number of addressable locations).

        And "conveyor-belt" would imply O(N) access time, which, in my book, is not RAM, but more like tape or HDD (possibly flying by at the speed of light, but still linear, not logarithmic!).

        But the experiment itself might be cool, everyone who have seen an optical table before should check out "A top view of the experiment" []

        • No, it would be O(1) for conventional RAM. You put the address on the address bus, toggle the control bits, and voila, the data is on the data bus. It makes no difference if the data is on the first page or the last page, or any place in between. It certainly does not depend on how big the RAM is.
          • How are you going to figure out *which* cell you're going to read from the RAM without looking at each of the O(log N) bits of the address? The decision to read from cell N depends on all O(log N) bits of N. It's not immediately obvious to me that *must* require O(log N) depth in your control circuitry, but it certainly isn't constant unless you allow unlimited fanin/fanout.

            • by Elbows ( 208758 )

              In practice, memory addresses on a given architecture have a fixed size (usually 32 or 64 bits), and the hardware can look at all the address bits in parallel, thus allowing O(1) access to any location in RAM. It's the same reason that you can add two integers in constant time.

              • by PaulBu ( 473180 )

                Of course O(log(N)) for *fixed* N is the same as O(1)! the dangers of O-notation is that in different contexts people can to disagree what relevant N is. Yes, you can sort N fixed-length integers in NlogN time, but what if integer length is growing?

                As to memory access, one can argue that there is also O(sqrt(N)) term in it for conventional semiconductor RAM, organized as squarish matrix: one can access it only as often as it takes to charge word line (with capacitance proportional to sqrt(N), where N is num

    • by Ihmhi ( 1206036 )

      If you want to be pedantic about it, all those little electron-y bits and whatnot move around in RAM too.

      So I guess I have four gigs of tape drives plugged into my motherboard right now.

  • Cool. (Score:5, Funny)

    by Nerdfest ( 867930 ) on Thursday September 10, 2009 @09:56PM (#29385615)
    It may, or may not, be useful.
  • meh (Score:3, Informative)

    by mindbrane ( 1548037 ) on Thursday September 10, 2009 @09:57PM (#29385625) Journal
    check it out [], i still dunno, so meh
  • by burning-toast ( 925667 ) on Thursday September 10, 2009 @10:34PM (#29385831)
    Quantum... heh... does that mean if you read your memory the data is destroyed? :-D
    • Re: (Score:1, Funny)

      by Anonymous Coward
      Nah, what it means is you can no longer refer to it as "tranny porn", it's "a superposition of states" porn.
    • No, simply that your data may or may not be there until you actually go to check it.

      Sort of like using NT Backup.
    • No, this is a special kind of quantum memory. The data is still there, it's only the storage mechanism that is annihilated [], so you'll want to stand well clear of it.

  • that this article follows the one about Turing...
  • by harryjohnston ( 1118069 ) <> on Thursday September 10, 2009 @11:16PM (#29386005) Homepage

    Unfortunately from the description it would appear that the memory is not quantum addressable ... that is, you can't use a set of qubits as the address of which qubit to read. For a fully general-purpose quantum computer, we will probably need quantum addressable memory.

  • by Cordath ( 581672 ) on Thursday September 10, 2009 @11:53PM (#29386163)
    While light can be bounced around, absorbed and re-emitted fairly well in a classical sense, it gets tricky when you start trying to store single photons that have been intentionally "dicked with" to encode quantum information. (i.e. Quantum bits, or qubits) What this paper is talking about is one way of implementing quantum memory for successfully storing and recalling photonic qubits. (i.e. light)

    Now, the computer geeks out there probably heard "qubits" and immediately thought "OooOOOooo... Quantum Computers!". Not so fast. Photonic qubits are generally too quick to decohere (even when stored in memory such as this) and difficult to interact with to be good candidates for quantum computing. It's certainly not impossible, and perhaps even probable in the long-run, but atomic qubits are currently more promising and more widely being looked at for quantum computing. What a photonic quantum memory is immediately useful for is communications. i.e. Quantum cryptography. More specifically, building quantum repeater networks.

    If you know a little about computer networks, you know that signals traveling over long distances have to be boosted by repeaters every so often or loss humps your data. Optical networks are exactly the same. After a few hundred kilometers of fiber you have a lot of loss. Unfortunately, unlike classical bits, which can simply be copied, qubits cannot be reliably copied. (Google the "no cloning" theorem if you care.) The work around is a little complex to explain (it's essentially a daisy chain of entanglement swapping), but requires quantum memory to work.

    The short of it is, this sort of quantum memory will allow us to build longer distance quantum encryption networks than currently exist. (Quantum crypto is currently being used by some European banks.) At first, this might allow banks in North America to jump on the Quantum bandwagon. It's hideously expensive at the moment, naturally, and probably less economical than running volkswagen's full of hard-drives with one-time-pads on them back and forth, but in principle nothing about this tech is any more expensive than the repeaters the internet currently runs on. Economy of scale should eventually kick in, and these quantum crypto networks will be pretty handy if quantum computers manage to toast public key encryption. (Authentication, of course, is another issue entirely...)

    Now, I haven't had a chance to read the Nature paper yet. I've read this groups past papers though, and they really are world leaders in experimental CRIB implementation. Last I checked, they still didn't have adequate efficiency to make their tech useable (must be greater than 50% recall to be practical). Still, CRIB is one of the more promising methods out there.
    • Re: (Score:3, Interesting)

      by Anonymous Coward

      Unfortunately, unlike classical bits, which can simply be copied, qubits cannot be reliably copied. (Google the "no cloning" theorem if you care.) The work around is a little complex to explain (it's essentially a daisy chain of entanglement swapping), but requires quantum memory to work.

      Correct me if I'm wrong here, but wouldn't that same work-around also allow someone to functionally tap into a quantum communications network, thereby invalidating the cryptographic utility of quantum communications?

      • by Cordath ( 581672 ) on Friday September 11, 2009 @01:51AM (#29386621)
        Depends on the type of network. For plain ol' BB84 systems relying on sending single qubit states, absolutely. You wouldn't use that over a quantum repeater network though. You'd likely use one of several quantum key distribution schemes relying on shared entanglement. (e.g. Ekert 92)

        Here's the principle on which quantum repeater networks will operate:

        Alice (----- Entangled Photon Pair Source -----) Bell State Measurement (------ Entangled Photon Pair Source -----) Bob

        What we want is for Alice and Bob to each wind up holding half of an entangled pair of photons. The two sources create two pairs of entangled photons and send the halves in opposite directions. Alice and Bob initially receive photons that have nothing to do with each other. However, when the other halves of Alice and Bob's pairs are annihilated together in the Bell State Measurement in the middle, the entanglement of the annihilated photons is swapped to Alice and Bob's photons such that they wind up being entangled together. The nice thing about this is that Alice and Bob can verify that they share entangled pairs and there's no way for anyone in the middle to fool them, provided Alice and Bob authenticate each other and there are no real-world deficiencies in their apparatus. In essence, Alice and Bob don't have to trust the man in the middle even though he's handling their photons.

        To build a quantum repeater network, you just expand this out in a giant daisy chain with many many steps. Quantum memory is necessary for caching photons at each node in the chain so that you can wait for all nodes to be ready before proceeding with the bell state measurements. Caching is necessary because the probability of photons reaching each of the stations in the network simultaneously is no better than the probability of one photon going from end-to-end. i.e. Not bloody likely over long distances.

        P.S. Funny aside: The first BB84 system built by Bennett and Brassard (the first quantum crypto system ever built), had some rather noisy pockel cell's controlling measurement bases such that you could tell what basis Alice was measuring in from the sound of the cell. Additionally, Alice and Bob were on the same lab bench, so an eavesdropper in between them would necessarily be inside the room. It was therefore famously joked that the first quantum crypto system was only secure if any potential eavesdropper was stone deaf! This is an example of a side-channel attack that can occur when reality doesn't quite live up to theory, and is the sort of thing people building any kind of crypto system, quantum or otherwise, have to worry about.
    • I wonder; as some start playing around with using quantum entanglement to create a not, do the string theorists start worrying about their jerking a knot in the universe(s?).
  • by Anonymous Coward
    ... is there anything you CAN'T do?
  • by Linker3000 ( 626634 ) on Friday September 11, 2009 @06:31AM (#29387843) Journal

    Can you just imagine it...

    "It looks like you want to save your last hour's edits to disk. Well, maybe they're in Quantum RAM, maybe they're not. Do you want me to have a look?"

    [YES] [NO] [BOTH]

  • "Damnit Al, why haven't I leaped!"
    "Ziggy says you have to manipulate the magnetic field first!"
  • And now all my porn's upside down.
  • I would love to tag it but, the new /. code doesn't allow Firefox to interact with the main page. For those of you using IE, I suggest you tag it with "RAQOM".

Never let someone who says it cannot be done interrupt the person who is doing it.