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Quantum Computing Breakthrough in Japan
An anonymous reader writes "A research team funded by NEC and RIKEN, Japan's Institute of Physical and Chemical Research, are the first to demonstrate a Controlled NOT (CNOT) quantum gate. The CNOT gate when coupled with a rotational gate would create a universal gate. The universal gate would be the basis for quantum computing. ETA for the first quantum computers: 10 to 100 years." When quantum computers first come to fruition, the best part will be reminiscing about how terrible computers were "back in the day."
All of todays encryption becomes irrelevant
It's possible to write very short computer programs that make useful calculations but would take a very long time to terminate. The reason that one who studies computer science is so concerned with Big-O estimates for algorithm running time is that some algorithms take so many steps that they are not feasible to implement - although writing the code for them might be simple. The faster you can compute operations, the fewer problems you have to ignore as being not feasible.
Quantum! The name does sound kind of cool. But try programming for one for a little while. That is something that you can do today with a simulator.
The only use for quantum computers in the future will be cryptography and very specially formulated problems. It won't run Quake VII or Windows 2015.
(Then again, if you chart processor and memory usage, you will find that nothing will run Windows 2015)
Modern schemes wouldn't be necessary because quantum cryptography would become the standard and is proven to be unbreakable by the laws of quantum mechanics.
Doesn't quantum cryptography require a point to point optic channel capable of successfully transmitting individual photons without interfering with their polarization (as well as detectors and receivers for such)? Even if people get fiber optic lines to their homes in the next few decades, I'm pretty sure we'll never see anything like that available to home users. If you want unbreakable cryptography today, you can use a one time pad with less inconvenience.
Not only that but they probably aren't the first to demonstrate in a solid either.
I worked in a lab that already did that late last year, in the Laser Physics Centre, ANU, as evidenced by a recent PhD thesis by Jevon Longdell, and many conference presentations. Although technically it was a controlled-phase gate, but they are functionally equivalent anyway.
Unfortunately writing papers takes a back seat to doing the work, so in the wider field few people know about it. It sucks to watch it happen.
The interesting thing about this method is that it is solid-state rather than some concoction of lasers and ultra-cold gasses.
Demonstration of conditional gate operation using superconducting charge qubits
T. YAMAMOTO1,2, YU. A. PASHKIN2,*, O. ASTAFIEV2, Y. NAKAMURA1,2 & J. S. TSAI1,2
1 NEC Fundamental Research Laboratories, Tsukuba, Ibaraki 305-8501, Japan
2 The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
* Permanent address: Lebedev Physical Institute, Moscow 117924, Russia
Correspondence and requests for materials should be addressed to T.Y. (yamamoto@frl.cl.nec.co.jp).
Following the demonstration of coherent control of the quantum state of a superconducting charge qubit, a variety of qubits based on Josephson junctions have been implemented. Although such solid-state devices are not currently as advanced as microscopic qubits based on nuclear magnetic resonance and ion trap technologies, the potential scalability of the former systems--together with progress in their coherence times and read-out schemes--makes them strong candidates for the building block of a quantum computer. Recently, coherent oscillations and microwave spectroscopy of capacitively coupled superconducting qubits have been reported; the next challenging step towards quantum computation is the realization of logic gates. Here we demonstrate conditional gate operation using a pair of coupled superconducting charge qubits. Using a pulse technique, we prepare different input states and show that their amplitude can be transformed by controlled-NOT (C-NOT) gate operation, although the phase evolution during the gate operation remains to be clarified...
CNOT has been done before. IBM in fact has demonstrated Shor's algorithm on 15 (the smallest number that can be factorized with that algorithm). This required 7 qubits.
If I remember correctly, the IBM experiment was done in a fluid state NMR system and as I understand it, they slightly cheat. They tackle the problem of decoherence, by throwing out non-coherent samples. However, all their quantum registers have to be within the same molecule and individualy addressable. In this case, they had 7 hydrogen atoms in some glycerol type molecule. Ofcourse, this makes scaling very difficult. In larger molecules, keeping the coherence under control becomes more and more difficult.
Storage is however difficult (keeping a superposition of qubits coherent for humanly-observable times is almost intractable)
Not completely true in atomic optical systems.
There have been experiments done with a Bose Einstein condensate (by Lene Hau) and in a simple vapor cell (in a group is Kaiserlautern), where they have imprinted the phase information of a laser beam on the atoms, effectively storing the light. In the case of Hau's experiment, the light could be recovered after upto a few hundred milliseconds.
Also, in experiments with single ions in a rf-trap, the coherence times turn out to be extremely long (only limited by the probability of the ion leaving the trap).
Furthermore, longer storage times are not really needed. For Shor's algorithm, you don't need a quantum harddrive, you only need quantum registers . You might argue that you need a coherent database for something like a Grover search, but there are a couple of nice ideas about that as well. Using something called a pulse-shaper, you can create very short laser pulses, that consist of multiple frequency components, that have a well determined phase with respect to each other. This pulse shaper is programmed with classical data, but if you shoot the pulses on a molecule, you can populate many excited states coherently, thus initializing you quantum registers. Grover searching have been performed in experiments in this way.
Quantum computers are interesting because they can carry out operations massively parallel by exploiting quantum states instead of by duplicating processing units. It's important to realise that this is a limiting factor of a quantum computer: It WILL NOT speed up problems that can't be restated to take advantage of the parallelism that a quantum computer offers.
The most likely use of quantum computers for the foreseeable future would be as simple co-processors for a conventional computer, with just a small number of qubits, as there are many smaller tasks that could likely be speeded up dramatically. Imagine doing string searches and comparisons where every character is compared against the pattern at once for instance - would have a dramatic impact on query times for databases and full text search systems... Systems depending on large amounts of matrix calculations would be another.
Applying quantum computing in piecemeal for algorithms that are small, self contained and frequently used will be immensely beneficial long before software engineers catch up and get experience with developing algorithms for quantum computers.
Disclaimer: I haven't spent much time reading up on quantum computers, so I'm likely completely clueless about the subject :-)
"Unless you have someone on a gray coat to take a bible inside a black suitcase chained to his arm to the recipient of your message."
As a matter of fact, I can, without problem, get a Multi Megabyte Key, available worldwide, without anyone the wiser...
It's called "Project Gutemberg", for one, or any place you can DL fixed texts,software or anything you like (say, what about usinf MS SP4 update as a key? it's available, and makes a key about 200Mo...)
OTP is real, works nice and is easily implementable. Internet got us here 8)
So, my DSL modem is black, and has a grey cat5 cable connected to it. I think I'll use it as my courrier 8)
It takes 40+ muscles to frown, but only four to extend your arm and bitchslap the motherfucker
"If you want unbreakable cryptography today, you can use a one time pad with less inconvenience."
I can't think of a more *IN*convenient method of cryptography. True OTP is nearly impossible because you would a) have to know the length of the data you're encrypting beforehand and b) exchange the OTP (ideally in person or in a worst-case over multiple channels) to make the encrypted data usable by more than just yourself. It's trivial to impliment the algorithm, unfortunately, the problem shifts to key management.
If you want to read the problem with OTPs, in Schneier's own words.. have a peek about 2/3 of the way down the page.
-AC
Just because it's hard to find an answer, doesn't mean it's hard to verify it. Consider the canonical example of factorisation - checking the results is trivial.
What good is a quantum computer for besides breaking encryption? It seems like that's the only problem-solving ability of quantum computers that is ever mentioned.
Why are you letting these clowns ruin our country?
I find it significant (and maybe a little alarming as well) that it was Japan, and not the U.S., who made this apparent breakthrough. To my eyes, although I would say "Congrats!" to the Japanese, it makes a pretty sad statement about how our own industrial base (read: large companies) values (or doesn't) heavy R&D and engineering.
How much engineering and R&D has been "outsourced" or "downsized" in the past two decades, in favor of delivering short-term "Shareholder Value?"
What happened to long-term survival and growth of a company vs. short-term profits? Just as two examples, Bell Labs is a pale shadow of what they once were, as is Boeing. How much further is it going to go before the U.S. is merely a mass "user" of the products that our "global partners" think up and turn out?
Bruce Lane, KC7GR,
Blue Feather Technologies
Picture these staggering fast processing speeds applied to genetic algorithms/programming. For those who don't know, in a very rough sense (don't nitpick) this involves:
1. You want a program that take input X and produces output Y
2. Generate a whole bunch of random programs. Most will do nothing even resembling producing the output Y, but some will suck more than others.
3. Feed the input X, and see what output each program produces. Take the least terrible program from the batch, make a bunch of copies
4. Then for each copy, change it randomly a little, eg flip a few bits.
5. If there isn't any program in the bunch that's good enough for you, go back to 3.
6. Otherwise, you have your program and didn't have to write it yourself. In fact, you don't even need to have the slightest idea how to solve the problem, just how to state it.
The only problem with this is that it may take a really, really long time to evolve an acceptable program. Often too long to be worth bothering. But with speeds as ridiculous as they propose for quantum computers, what program couldn't you evolve in say, a day? Or, for that matter, why not just generate every possible piece of machine code of a given length, run them all through an emulator at sickening speeds, and see if any of them solved the problem? I think that if you have truly sick processing power like this, then almost any problem is solvable with relative ease. Maybe I overstate the case, but you see what I'm getting at.