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July 07, 2008

Dwave showing some experimental proof of quantum coherence matching Landau Zener Transitions for their quantum computer

Dwave Systems is a company that is trying to make commercial quantum computers is solidifying the theoretical and experimental evidence that they have in fact created quantum computers. Dwave should be releasing quantum computers with thousands of qubits before the end of 2008. A successful implementation of a true quantum computer will make certain classes of tough math and science problems many billions of times faster to solve. For example, the formula for calculating the solving time can change from N**4 to N * square root of N where N is the size of the problem to be solved. Bottom-line. A lot of interesting and useful things that are not solvable now become solvable.

Seth Lloyd is a co-author of the research paper and he leads a quantum information research group at MIT
Seth Lloyd has performed seminal work in quantum computing and quantum communication

There are encryption schemes which are resistant to quantum computers. So ecommerce can be made secure even if there are successful quantum computers. These AQC (Adiabatic Quantum computers) are not well suited to running the Shor algorithm for breaking encryption.



Dwave Systems finds that the behavior of their qubit agrees to a high degree of accuracy with theoretical predictions for Landau-Zener transition probabilities for a double-well quantum system coupled to 1/f magnetic flux noise. They demonstrate that in this large decoherence limit, the quantum mechanical behavior of this qubit is the same (except for possible renormaliza-
tion of ¢) as that of a noise-free qubit, as long as the energy bias sweep covers the entire region of broadening W.

They have published a paper on these LZ transition experimental tests. "Landau-Zener Transitions in an Adiabatic Quantum Computer"
J. Johansson, M.H.S. Amin, A.J. Berkley, P. Bunyk, V. Choi, R. Harris, M.W. Johnson, T.M. Lanting, Seth Lloyd, and G. Rose

The close agreement between theory and experiment for a single qubit undergoing a LZ transition in the presence of noise supports the accuracy of our dynamical models, including both the noise model and the model of a single superconducting qubit that has been isolated from its surrounding qubits in an adiabatic quantum computer. Future experiments will test the behavior of multiple coupled qubits undergoing a LZ transition in the presence of noise.



Dwave's CTO Geordie Rose writes on Landau-Zener Quantum Computation

The probability of remaining in the ground state after an LZ transition doesn’t depend on the environment at all for broad classes of QC-environment couplings. This is another facet of the wonderful inherent noise-resistant properties of the AQC model, and is a great example of how many-body physics can help reveal deep truths about quantum information theory.

While we continue to call the model AQC, I think it’s fair to say that maybe because of our solid-state physics bias we’re thinking of it more and more as LZQC.


FURTHER READING
Seth Lloyd of MIT on Dwave systems. Seth is a co-author of the recent paper.

There are algorithms for encryption which would be resistant to Shor's algorithm on quantum computers. So we would still be able to encrypt financial transactions.

Wikipedia on Landau-Zener transition/formula

Wikipedia on Adiabatic theorem



Quantum annealing could be millions of times faster than classical computers

Quantum computers could make very powerful pattern matchers

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