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Quantum Computing Using Traditional Transistors
Ocean Consulting writes "UCLA is reporting progress on the quantum computing front by announcing success in controlling the spin of a single electron using an ordinary transistor." It's been a long road for the researchers involved, and even the project lead, Hong Wen Jiang admits, "...our initial theoretical calculations were very favorable, and gave us confidence to persevere."
This would be something to help drive down the cost. Quantum computing on the desktop would finally be a evolutionary step in computing. (Up'ing clockspeed constantly and decreasing chip size is not evolutionary.) Though, quantum computing on the desktop probably means time to stop using passwords due to sheer power to brute force them.
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They're actually using pulsed microwave bursts to manipulate the electron's spin, not the transistor itself, really.
Most encryption algorithms rely on it being easier to multiply numbers than to factorise them. Quantum computers can easily factorise a large number into a product of primes.
This is how quantum computers can break encryption
I'm not sure what they mean by the encryption that is secure though; Quantum encrytion as such is completely separate from Quantum computers, it is just a clever method using detection of the polarisation of light.
The sending computer begins by sending photons in one of four configuations, two each for the x shape and + shape
The detectors can only tell the difference between the two states if they are detecting using the correct shape.
The reciever then transmits a list saying which detector shape it used for each bit, and the sender sends back information saying when it was a correct guess, thus establishing a cipher key
Now, if someone is intercepting the signal, they will not guess the same way as the reciever, thus they wont have the cipher key at the end (I can't remember if they are detectable becuase they screw with the polarisation or not).
Thus unbreakable crytography.
[Disclaimer: IANAPhysicist, and I know that because I read The Code Book by Simon Singh. He describes it properly and accurately (both secure cryptography and breaking today's algorithms with quantum computers)]
ah, mod points
It is secure and it allows encrypted communications to be spied on. What they don't tell you is that the encrypted comunications are encrypted using standard encryption methods around today. Things that can be cracked by exhaustive search.
Using a quantum computer it can search every possible key simultaneously, cracking the encryption almost instantly. An example to understand this, you are in a building searching for your briefcase. Normal computers would go through every room one by one until they find it. A quantum computer would find the briefcase by existing in every room at the same time, finally settling (existance wise) in the room with the briefcase.
They also mention quantum cryptography being uncrackable, this is true. If someone eaves drops on communication that is encrypted, it inherently destroys the data. The users will recognize intrusion and the eavesdropper cannot decrypt the message because the data has been destroyed.
So yes, quantum computers can decrypt normal encryption that can be broken by exhaustive search and they can be used to provide quantum cryptograph which is a theoretically unbreakable form of communication.
They're talking about communications where if someone is snooping on the conversation you will know it. This is done using entanglement. Here's a real world example:
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http://www.newscientist.com/news/news.jsp?id=ns99
I believe people are already doing this with fiber optics. You can detect very accurately if someone is tapping a fiber optic channel.
Yes, quantum communication is not magically DOS proof.
taken! (by Davidleeroth) Thanks Bingo Foo!
The quantum channel is only used for creating one-time pads (OTP). The channel is eavesdrop-sensitive so you know which bits are compromised and you don't use them in the OTP. Then when you have generated a large enough shared OTP, you use it to encrypt the message and simply send that over regular channels, and since no one else has your securely generated OTP, that message is unbreakable.
taken! (by Davidleeroth) Thanks Bingo Foo!
how about a lot more then the amount of pr0n you can watch during your lifetime?
The following link may be helpful for those of us who are a little fuzzy on quantum computing: http://www.cs.caltech.edu/~westside/quantum-intro. html
As someone who has taken a course in quantum computing, I can tell you that this article has numerous inaccuracies and misleading statements. The section you highlight is an example. Many current encryption algorithms are based on the fact that it is difficult to factor large numbers (products of two primes). An algorithm for doing so efficiently has already been developed for quantum computers. So, as soon as we can build quantum computers (larger than a few qbits), today's toughest encryption algorithms will essentially become obsolete overnight.
However, quantum computing also provides a secure means of communication. This means of communication is not secure because it uses some fancy cryptographic coding; it is "secure" because of the way it makes use of quantum physics, as opposed to classical physics. In essence, if two parties are communicating through a quantum channel using a secure quantum communication protocol, it is impossible for a third party to eavesdrop on the conversation. Note: I really mean impossible. Not just "difficult but maybe possible in the future with more processing power". I mean impossible as in doing so would require breaking the laws of physics (as we understand them today). An attempt to eavesdrop would (a) irrecoverably corrupt the data being communicated, and (b) be detectable by both parties (so they could halt communications as soon as the attempt to eavesdrop was detected). The probability that an eavesdropper would be successfull is vanishingly small. I.e., the eavesdropper would basically have to "guess" correctly for each bit of the communication.
So, the statement the article makes is innane. Sure, existing encryption algorithms will be easily breakable with quantum computers. But because of that, no one who cares about security will use them anymore. What's to stop terrorists from using their own quantum computers and communication channels? It will be as impossible for the government to intercept their communications as it will be for terrorists to intercept the government's communications. The same goes for the average user - you and me.
Our privacy may be "sacrificed" for a short transitionary period (in which some people have quantum computers but others still use classical encryption), but this will only last until quantum computers become commercially viable. Quantum computing is a big win for our privacy in the long run!
First off: I am not an expert, just someone who watches this closely and has read a lot of books on the subject. (Hint: The fabric of reality and Quest for the Quantum computer are very good, not to difficult to read)
...But: what is good about this is that it is being done with conventional approaches: an ordinary transistor. Now they can use everything that is known to transistors to proceed and make it better. (what is not so good is that they still need to do it at _very_ low temperatures.)
In a sense, nothing has been achieved here that hasn't been achieved with other methods. These guys are strugling with just one quantum spin, which doesn't even make one qubit (you have to do more) where others like some researchers from IBM have already combined 4 qubits. Making just one qubit isn't all that difficult these days, but combining them in a way that they are still usable is increasingly difficult when the number of qubits increases. It's called the problem of decoherence.
Please login to access my lawn
Must confess I am being pedantic here, so I may be annoying, but....
Usual 3 dimensional spin is characterized by speed (revolutions per second) and the axis the object is spinning about.
Yes, but with quantum mechanical particles, nothing is spinning. There is not one part of an electron that is rotating about another. (see my warning about 'pedantic' above!)
Flipping spin means reversing the axis - i.e. changing the direction of rotation.
But with quantum mechanical particles, there is no real 'direction' - its a relative property, and direction is meaningless when there are only limited states.
Its a metaphor, an analogy, and that is all. We have absolutely no idea what is 'really' happening at the 'electron' level. All we have is some math that gives answers. I strongly believe that using terms like 'spin' gives a false impression of understanding. Eventually terms like 'spin' and 'orbit' are so frequently used they crowd out alternative metaphors.
My understanding was that this is not true. At best you get the square root of the number of steps that would be required for a non-quantum brute force search. This means that key sizes are effectively halved, but that isn't an insurmountable problem.
Bingo. Which is why the AES competition required support for 256 bit keys, when even 128 bits is out of reach by any conceivable technology.
Factoring is one such case, which is why quantum computing spells the death of RSA.
Not true, necessarily. Shor's algorithm is algorithmically faster than the generalized number field sieve, but there is a constant in there. We don't know how big that constant is, and we won't until we have a quantum computer big enough to run Shor's algorithm (30 qubits or so, IIRC). It's entirely possible that Shor's algorithm is only faster then the GNFS once you hit keysizes of 10,000 bits, in which case it doesn't matter. OTOH, if Shor's algorithm is faster than the GNFS on 256 bit keys, we are, indeed, in some trouble. Of course running Shor's algorithm on a 1024 bit RSA key would take quite a large quantum computer, too.
And, as you mention, there is no algorithm for compute discrete logarithms much faster than usual on quantum computers. I haven't heard about such an algorithm, anyway. Doesn't mean it doesn't exist, of course.
Summary: algorithmic complexity is not the sole determinant of algorithm running time.
In summary, quantum computing is powerful, but not a magic wand that makes all classical encryption schemes invalid.
Thank you. Every time a quantum crypto or quantum computing store pops up here, the hype level seems to increase by several orders of magnitude. It's really annoying.
Saying that something is spinning in the classical sense imputes an angular momentum on the object. But the quantum of angular momentum has different units than the quantum of spin. Hence, quantum spin is fundamentally different from classical spin. And this is one of the rationales that has been argued for decades for why quantum spin should be given another name.