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First 'Quantum Computer Chips' Demonstrated
holy_calamity writes "The first quantum computer chips have been made by two US groups, New Scientist reports. Both NIST and Yale have demonstrated chips where information was transferred between two superconducting qubits using a 'quantum bus'. The bus is made from a cavity that traps a single microwave photon as a standing wave — the NIST group also managed to use the bus to store data from one qubit for a short time. 'After encoding information in one qubit, they transferred it into the cavity for 10 nanoseconds before transferring it to the other qubit. Yale's chip used qubits around 1-micron square built on silicon, while NIST used larger 10-square-micron qubits on top of sapphire. In both prototypes, the bus between the qubits was between five and seven millimeters long.'"
I think what he was getting at is factoring a number quickly is very slow (np-complete) on todays hardware. With Quantum computers the problem does not take as long just like the NSA and some research groups try and break current encryption with a grid of computers because they just brute force their way past the encryption. The reason your average joe does not do this is because most people can not afford a large grid of computers. Well with quantum computers your average joe may not need a large grid of computers.
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Because, in theory, quantum superposition can be exploited to provide keys of arbitrary length; since each qubit can be 0 and 1 simultaneously, put enough qubits together and you ALWAYS have the right key.
The quantum chips TFA references are not designed around this principle, so this is all a little unrelated, but there is a reason why people expect widespread quantum computing to bring about the end of the useful life of today's ciphers.
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My understanding is quantum entanglement cannot be used to transfer information.
Well, it has never been successfully tested.
Yes, D-Wave's device is on a chip, but there are others long before that, too. I am not sure what the first solid-state qubit experiment was, but such experiments have been going on since the late 90's. The claim of these experiments is that they demonstrate the first quantum bus on a chip.
Readers may find the Yale group's press release interesting.
No, this is not correct. While it's true that if you put N qubits together in the correct superposition, you can make a state that is "equally spread out" over all 2^N possibilities, you cannot make the computer "favor" the correct one (at least not in the sense you are implying). Using Shor's algorithm you can factor a number in O((log N)^3), which is an exponential improvement to crack RSA. And yes, I am a physicist working on quantum computing.
"I think I can safely say that nobody understands quantum mechanics." - Richard Feynman
A superposition of states simply means that that the particle has an unknown value for the property being discussed. If you pick any random electron up off the street, its spin along any axis you choose to measure is in a superposition of states such that it might be up or down with equal probability. You can't measure this condition of being in a superposition of states because it is not a property of the electron. Rather, it is a condition of the information that you know about the electron. To use a bad coin flipping analogy, if you flip a coin and cover it before looking, you can say it is in a superposition of states between heads and tails with equal probability of each, not because there is anything special about the coin but because you simply don't know the definite answer.
Entanglement does not allow you to control anything at all about a distant particle. When particles are entangled, that means that measurements taken on both members of an entangled pair will correlate more often than our current understanding of the universe says should be possible. The measuring is a passive thing -- it gets information about the state of the particle. The correlations imply that somehow the entangled particles are linked over distance, or that the future of the pair of particles was predetermined at the time the entangled particles were created.
It cannot be exploited for communication because in order to even detect the strange correlations, you have to compare measurements, which requires getting information about those measurements to a common location. Suppose I'm doing an experiment with entangled photon polarization, and Alice is trying to send a message by modulating the angle of her polarizer. At Bob's detector, he's getting a 50% hit/miss with each photon that comes his way, no matter what angle Alice sets her polarizer to, and his measurement results are completely random.In order for Bob to decode the message, he has to know what Alice's measurements were. This is actually why photon entanglement is useful for encryption -- but it ain't gonna let us talk faster than light.
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