November 26, 2005

Other tech: Holographic-memory discs may put DVDs to shame

The discs, developed by InPhase Technologies, based in Colorado, US, hold 300 gigabytes of data and can be used to read and write data 10 times faster than a normal DVD. The company, along with Japanese partner Hitachi Maxell announced earlier in November that they would start selling the discs and compatible drives from the end of 2006. InPhase says the technique could theoretically be used to store up to 1.6 terabytes of data on the same size of disc and to read data at 120 megabits per second. This is 340 times the capacity of an ordinary DVD and 20 times the data rate.

November 24, 2005

Possible Path to 100+ Qubit Quantum computers

It seems that bubbles of electrons lined up in ultracold liquid helium could be used to build a quantum computer capable of carrying out a staggering 10 to the 30th power simultaneous calculations. To make an electron bubble, start with liquid helium that has been cooled below 2.17 kelvin so that it behaves like a superfluid, a state of matter with zero viscosity. Now inject a fast-moving electron into the superfluid. When the electron eventually slows to a halt after numerous collisions with helium atoms, it creates a cavity about 3.8 nanometres across by repelling nearly 700 atoms' worth of helium around it (New Scientist, 14 October 2000, p 24).

It is this cavity that makes the electron bubble so very valuable. In a quantum computer, the quantum entities need to be isolated from their surroundings to preserve their fragile states. "What could be more isolated than an electron in a bubble?" asks Weijun Yao of Brown University in Providence, Rhode Island the originator. "The electron inside each bubble interacts very weakly with the background helium atoms."

Yao says 0s or 1s could be encoded in the electrons' spins. In the presence of a magnetic field, the spin can either be parallel or anti-parallel to the field. Crucially, an electron's spin can exist in both states at the same time, enabling the qubit to be both 0 and 1.

According to Yao, large numbers of electrons, each in its own bubble, can be neatly caged using a combination of a device called a linear quadrupole trap, which traps the electrons in a line, and a set of conducting rings, which create a voltage "valley" for each bubble (see Diagram).

All the spins can be initialised to the same value by cooling the apparatus to 0.1 kelvin. You can then manipulate the electrons by applying a combination of a magnetic field gradient along the line and varying the frequency of the voltages in the quadrupole trap. This changes the spin of individual electrons and makes them interact to perform logicgate operations ( cond-mat/0510757). To read the spin of an electron, the voltage at the end of the electron chain can be lowered so that each bubble drifts in the magnetic field gradient at a velocity that depends on the electron's spin. This drift velocity can be read using lasers.

Because each qubit carries two values, a quantum computer with two qubits could carry out four parallel calculations, one with three qubits eight calculations, and so on. "I see no major technical obstacles to the system I envisage working with 100 qubits," says Yao. "That means it could do 1000 billion billion billion operations all at once."

New Tool: Inside a quantum dot: Tracking electrons at trillionths of a second

New Research Enabling Tool: Researchers at the EPFL (Ecole Polytechnique Federale de Lausanne) have developed a new machine that can reveal how electrons behave inside a single nano-object. The results from initial tests on pyramidal gallium-arsenide quantum dots are presented in an article in the November 24 issue of Nature. The machine developed by Professor Benoit Deveaud-Pledran and his EPFL colleagues is the first tool that can track the passage of an electron in a nanostructure – at a time scale of ten picoseconds and a spatial resolution of 50 nanometers.

The EPFL researchers replaced the standard electron gun filament on an off-the-shelf electron microscope with a 20 nanometer-thick gold photocathode. The gold is illuminated by an ultraviolet mode-locked laser, generating an electron beam that pulses 80 million times per second. Each pulse contains fewer than 10 electrons. The electrons excite the sample, causing it to emit light. The spectroscopic information is collected and analyzed to recreate the surface morphology and to trace the path the electrons follow through the sample.

Deveaud-Pledran and his colleagues tested their new machine on pyramidal quantum dots. These 2-micron-high nano-objects, specially synthesized in the lab of EPFL professor Eli Kapon, contain several different nanostructures, making them ideal test objects. When the electron beam impacts the pyramid, the electrons diffuse towards the closest nanostructure. From there, the diffusion continues until the point of lowest energy is reached -- the quantum dot at the tip of the pyramid. The time traces corresponding to each of these nanostructures reveal just how critical that 10- picosecond time resolution is; with even a 100-picosecond resolution, important information would be lost.

November 21, 2005

The Impossible Is Possible: Laser Light from Silicon

\Now a trio of Brown University researchers, led by engineering and physics professor Jimmy Xu, has made the impossible possible. The team has created the first directly pumped silicon laser. They did it by changing the atomic structure of silicon itself. This was accomplished by drilling billions of holes in a small bit of silicon using a nanoscale template. The result: weak but true laser light. Results are published in an advanced online edition of Nature Materials. In order to make his silicon laser commercially viable, Xu said, it must be engineered to be more powerful and to operate at room temperature. (Right now, it works at 200°C below zero.) But a material with the electronic properties of silicon and the optic properties of a laser would find uses in both the electronics and communications industries, helping to make faster, more powerful computers or fiber optic networks. the team created a template, or “mask,” of anodized aluminum. About a millimeter square, the mask features billions of tiny holes, all uniformly sized and exactly ordered. Placed over a bit of silicon then bombarded with an ion beam, the mask served as a sort of stencil, punching out precise holes and removing atoms in the process. The silicon atoms then subtly rearranged themselves near the holes to allow for light emission.

The creation of billions of holes could be done more precisely if molecular nanotechnology capabilities existed. These kinds of material alterations to generate new properties would be more commonplace at that point.

Discussion of ranking countries in nanotechnology

A Lux Research article divides nations are into four categories. The details are discussed at soft machines. Dominant (USA, Japan, Germany and South Korea) - strong both in basic research and commercialisation, Ivory Tower (UK and France), strong in basic research but weaker in commercialisation, Niche Players (Israel, Singapore and Taiwan), weaker in basic research but strong in commercialisation of selected regions. China falls into the Minor League category, weak on both measures, and so not even in the top nine of nanotech powers. The report does suggest that China is moving strongly forward but there is no suggestion that it will overtake the current leaders. China is starting to spend more and publish more. The press release focuses on china “CHINA: MOVING FROM LAGGARD TO POWER PLAYER IN NANOTECHNOLOGY”. The recent Lux research study was based on aggregated a total of 17 metrics, of which the publications count and total spending. China was still weak both in nanotechnology activity and in its capacity to use nanotechnology to drive economic growth. Tntlog discusses how not all spending is equal and soft machines has an article that not all research publishing is equal.

Advancement in the creation of nanostructures using Scanning tunneling Microscopes

Francesca Moresco and colleagues at Freie University in Berlin said the interaction between the tip of a STM and atoms or molecules bound to a surface can be used to construct impressive nanostructures, such as the quantum corral. The researchers said they combined STM manipulation techniques with the ability of a molecule to assemble nanostructures by sucking up and depositing atoms where needed. Moresco and colleagues say they go a step further by moving and organizing metal atoms on a substrate with the help of a well-designed six-leg organic molecule.

The research is detailed in the in the December issue of Nature Materials.

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