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Nasa buys into 'quantum' computer

A $15m computer that uses "quantum physics" effects to boost its speed is to be installed at a Nasa facility.
It will be shared by Google, Nasa, and other scientists, providing access to a machine said to be up to 3,600 times faster than conventional computers.
Unlike standard machines, the D-Wave Two processor appears to make use of an effect called quantum tunnelling.

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Quantum cryptography
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More accurate than Heisenberg allows? - Uncertainty in the presence of a quantum memory

Quantum cryptography is the safest way to encrypt data. It utilises the fact that transmitted information can only be measured with a strictly limited degree of precision. Scientists at Ludwig-Maximilians-University (LMU) in Munich and ETH Zürich have now discovered how the use of a quantum memory affects this uncertainty.
A quantum particle is hard to grasp, because one cannot determine all its properties precisely at the same time. Measurements of certain parameter pairs such as position and momentum remain inaccurate to a degree given by Heisenberg's Uncertainty Principle. This is important for the security of quantum cryptography, where information is transmitted in the form of quantum states such as the polarisation of particles of light.

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Title: Towards high-speed optical quantum memories
Authors: K. F. Reim, J. Nunn, V. O. Lorenz, B. J. Sussman, K. C. Lee, N. K. Langford, D. Jaksch & I. A. Walmsley

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers and quantum communications. To date, quantum memories have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in caesium vapour.

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Quantum computer hits hydrogen bullseye

A basic quantum computer has successfully tackled one of the most challenging tasks facing chemists today - calculating molecular energy from basic scientific principles.
Although knowing a molecule's energy can help predict reaction rates, the computer power needed and complexity of working it out from first principles forces chemists to use approximations, which may be inaccurate. Andrew White of the University of Queensland, Australia, explains that a 2005 study calculated full models for hydrogen and helium, but couldn't go any further.

'They said that for the foreseeable future lithium looks impossible. If you took a molecule with 100 electrons, you couldn't even solve that using every computer in the world at once.'

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"One of the most important problems for many theoretical chemists is how to execute exact simulations of chemical systems. This is the first time that a quantum computer has been built to provide these precise calculations" - Alán Aspuru-Guzik, assistant professor of chemistry and chemical biology at Harvard.

In an important first for a promising new technology, scientists have used a quantum computer to calculate the precise energy of molecular hydrogen. This groundbreaking approach to molecular simulations could have profound implications, not just for quantum chemistry, but also for a range of fields from cryptography to materials science.

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The latest quantum algorithm is generating excitement among physicists. It tackles linear equations: expressions such as 3x + 2y = 7 and typically written with unknowns on one side and constants on the other. Many high schoolers learn the trite mechanics of solving systems of such equations by eliminating one unknown at a time. Speed becomes crucial when systems contain billions of variables and billions of equations, which are not unusual in modern applications such as simulations of weather and other physical phenomena. Efficient algorithms can solve large, "N by N" systems (systems having N linear equations and N unknowns) by computer. Still, calculation time grows at least as fast as N does: if N gets 1,000 times larger, the problem will take at least 1,000 times longer to solve, often more.
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First-ever calculation performed on optical quantum computer chip
A primitive quantum computer that uses single particles of light (photons) whizzing through a silicon chip has performed its first mathematical calculation. This is the first time a calculation has been performed on a photonic chip and it is major step forward in the quest to realise a super-powerful quantum computer.

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Scientists closer to build a practical quantum computer
Physicists at the National Institute of Standards and Technology (NIST), US, have demonstrated sustained, reliable information processing operations on electrically charged atoms (ions), thus raising prospects for building a practical quantum computer.
The new work overcomes significant hurdles in scaling up ion-trapping technology from small demonstrations to larger quantum processors.

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