Saturday, May 14, 2011

Another quantum computer

AAAS Science reports:
Four years ago, an upstart tech company created a stir when it claimed to have built a quantum computer—a thing that, in principle, could solve problems ordinary computers can’t. Physicists from D-Wave Systems in Burnaby, Canada, even put on a demonstration. But other researchers questioned whether there was anything quantum mechanical going on inside the device. Now, the D-Wave team has published data that they say prove quantum phenomena are at work within its chip. ...

The results won’t end the controversy over D-Wave's technology, however. ...

Stay tuned. Johnson says the D-Wave team members will have more publications to back up their claim that they really have a quantum computer.
The research has been published in (UK) Nature:
This programmable artificial spin network bridges the gap between the theoretical study of ideal isolated spin networks and the experimental investigation of bulk magnetic samples. Moreover, with an increased number of spins, such a system may provide a practical physical means to implement a quantum algorithm, possibly allowing more-effective approaches to solving certain classes of hard combinatorial optimization problems.
I am seeing a pattern here. Someone makes a dubious quantum computer claim. There is some skepticism. The researchers say that a real quantum computer is just around the corner. No one wants to admit that quantum computers are impossible.

Here is more info:
To demonstrate quantum annealing, the researchers first adjusted the eight qubits to resemble a 1D chain of magnets, where each qubit wants to point in the same direction (up or down) as its two neighbors. The researchers then set the qubits on the ends of the chain in opposite directions, and allowed the six qubits in the middle to orient their spins with their neighbors. Since this set-up forces two neighboring qubits to have opposing spins, the process resulted in a “frustrated” ferromagnetic arrangement. Then, by tilting the qubits in the same direction and raising the energy barrier, the researchers caused the system to move toward one specific arrangement of frustrated spins, which is the ground state.

Qubits can flip spins in two ways: through a quantum mechanical mechanism (tunneling) and a classical mechanism (thermal activation). Since thermal activation destroys the quantum nature of the qubit, the researchers had to show that the qubits were flipping spins due solely to quantum tunneling. They did this by applying a current to the system until both tunneling and heat-driven transitions stopped, and the qubit “froze.” By repeating this process at different temperatures, the researchers could determine that annealing occurred by tunneling alone. In other words, the results cannot be explained by classical physics.
This is supposedly the proof for an 8-qubit computer. It is a scam.

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