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October 14, 2008

Quantum Key communication 100 times faster, tunable Josephson metamaterial

1. Toshiba Research Europe Ltd, a company belonging to the Toshiba group, achieved a quantum key data transmission speed of 1.02Mbps at a distance of 20km, which is 100 times faster than conventional speeds.

Also, a speed of 10.1Kbps was demonstrated at a transmission distance of 100km, according to the company. This was made possible by adopting an APD (avalanche photo diode), which is usually used for optical communication, as a single photon detector and enhancing the drive frequency of the detector to more than 100 times higher than the conventional frequency, Toshiba said.






Items 2 through 4 are from Nature Physics advanced online publication:


In the JILA/NIST “noiseless” amplifier, a long line of superconducting magnetic sensors (beginning on the right in this colorized micrograph) made of sandwiches of two layers of superconducting niobium with aluminum oxide in between, creates a 'metamaterial' that selectively amplifies microwaves based on their amplitude rather than frequency or phase. Credit: M. Castellanos-Beltran/JILA

2. Amplification and squeezing of quantum noise with a tunable Josephson metamaterial could increase the speed and precision of quantum computers.

M. A. Castellanos-Beltran, K. D. Irwin, G. C. Hilton, L. R. Vale & K. W. Lehnert

It has recently become possible to encode the quantum state of superconducting qubits and the position of nanomechanical oscillators into the states of microwave fields. However, to make an ideal measurement of the state of a qubit, or to detect the position of a mechanical oscillator with quantum-limited sensitivity, requires an amplifier that adds no noise. If an amplifier adds less than half a quantum of noise, it can also squeeze the quantum noise of the electromagnetic vacuum. Highly squeezed states of the vacuum can be used to generate entanglement or to realize back-action-evading measurements of position. Here we introduce a general-purpose parametric device, which operates in a frequency band between 4 and 8 GHz. It adds less than half a noise quantum, it amplifies quantum noise above the added noise of commercial amplifiers and it squeezes quantum fluctuations by 10 dB.


Azonano has more information on the new quantum amplifier

3. Entanglement theory and the second law of thermodynamics.

Fernando G. S. L. Brandão & Martin B. Plenio

Entanglement is central both to the foundations of quantum theory and, as a novel resource, to quantum information science. The theory of entanglement establishes basic laws that govern its manipulation, in particular the non-increase of entanglement under local operations on the constituent particles. Such laws aim to draw from them formal analogies to the second law of thermodynamics; however, whereas in the second law the entropy uniquely determines whether a state is adiabatically accessible from another, the manipulation of entanglement under local operations exhibits a fundamental irreversibility, which prevents the existence of such an order. Here, we show that a reversible theory of entanglement and a rigorous relationship with thermodynamics may be established when considering all non-entangling transformations. The role of the entropy in the second law is taken by the asymptotic relative entropy of entanglement in the basic law of entanglement. We show the usefulness of this approach to general resource theories and to quantum information theory.


4. Reliable neuronal logic devices from patterned hippocampal cultures. Cultures of living neurons are patterned in a way to form functional logic devices.

Ofer Feinerman, Assaf Rotem & Elisha Moses

Functional logical microcircuits are an essential building block of computation in the brain. However, single neuronal connections are unreliable, and it is unclear how neuronal ensembles can be constructed to achieve high response fidelity. Here, we show that reliable, mesoscale logical devices can be created in vitro by geometrical design of neural cultures. We control the connections and activity by assembling living neural networks on quasi-one-dimensional configurations. The linear geometry yields reliable transmission lines. Incorporating thin lines creates 'threshold' devices and logical 'AND gates'. Breaking the symmetry of transmission makes neuronal 'diodes'. All of these function with error rates well below that of a single connection. The von Neumann model of redundancy and error correction accounts well for all of the devices, giving a quantitative estimate for the reliability of a neuronal connection and of threshold devices. These neuronal devices may contribute to the implementation of computation in vitro and, ultimately, to its understanding in vivo.

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