The odd behavior of a molecule in an experimental silicon computer chip has led to a discovery that opens the door to quantum computing in semiconductors.

In a Nature Physics journal paper currently online, the researchers describe how they have created a new, hybrid molecule in which its quantum state can be intentionally manipulated - a required step in the building of quantum computers.

“Up to now large-scale quantum computing has been a dream,” says Gerhard Klimeck, professor of electrical and computer engineering at Purdue University and associate director for technology for the national Network for Computational Nanotechnology.

“This development may not bring us a quantum computer 10 years faster, but our dreams about these machines are now more realistic.”

The workings of traditional computers haven’t changed since they were room-sized behemoths 50 years ago; they still use bits of information, 1s and 0s, to store and process information. Quantum computers would harness the strange behaviors found in quantum physics to create computers that would carry information using quantum bits, or qubits. Computers would be able to process exponentially more information.

If a traditional computer were given the task of looking up a person’s phone number in a telephone book, it would look at each name in order until it found the right number. Computers can do this much faster than people, but it is still a sequential task. A quantum computer, however, could look at all of the names in the telephone book simultaneously.

Quantum computers also could take advantage of the bizarre behaviors of quantum mechanics - some of which are counterintuitive even to physicists - in ways that are hard to fathom. For example, two quantum computers could, in concept, communicate instantaneously across any distance imaginable, even across solar systems.

Albert Einstein, in a letter to Erwin Schrödinger in the 1930s, wrote that in a quantum state a keg of gunpowder would have both exploded and unexploded molecules within it (a notion that led Schrödinger to create his famous cat-in-a-box thought experiment).

This “neither here nor there” quantum state is what can be controlled in this new molecule simply by altering the voltage of the transistor.

Until now, the challenge had been to create a computer semiconductor in which the quantum state could be controlled, creating a qubit.

“If you want to build a quantum computer you have to be able to control the occupancy of the quantum states,” Klimeck says. “We can control the location of the electron in this artificial atom and, therefore, control the quantum state with an externally applied electrical field.”

The discovery began when Sven Rogge and his colleagues at Delft University of Technology in the Netherlands were experimenting with nano-scale transistors that show the effects of unintentional impurities, or dopants. The researchers found properties in the current-voltage characteristics of the transistor that indicated electrons were being transported by a single atom, but it was unclear what impurity was causing this effect.

Physicist Lloyd Hollenberg and colleagues at the University of Melbourne in Australia were able to construct a theoretical silicon-based quantum computer chip based on the concept of using an individual impurity.

“The team found that the measurements only made sense if the molecule was considered to be made of two parts,” Hollenberg says. “One end comprised the arsenic atom embedded in the silicon, while the ‘artificial’ end of the molecule forms near the silicon surface of the transistor. A single electron was spread across both ends.

“What is strange about the ’surface’ end of the molecule is that it occurs as an artifact when we apply electrical current across the transistor and hence can be considered ‘manmade.’ We have no equivalent form existing naturally in the world around us.”

Klimeck, along with graduate student Rajib Rahman, developed an updated version of the nano-electronics modeling program NEMO 3-D to simulate the material at the size of 3 million atoms.

“We needed to model such a large number of atoms to see the new, extended quantum characteristics,” Klimeck says.

The simulation showed that the new molecule is a hybrid, with the naturally occurring arsenic at one end in a normal spherical shape and a new, artificial atom at the other end in a flattened, 2-D shape. By controlling the voltage, the researchers found that they could make an electron go to either end of the molecule or exist in an intermediate, quantum, state.

This model was then made into an image by David Ebert, a professor of electrical and computer engineering at Purdue, and graduate student Insoo Woo.

Delft’s Rogge says the discovery also highlights the current capabilities of designing electronic machines.

“Our experiment made us realize that industrial electronic devices have now reached the level where we can study and manipulate the state of a single atom,” Rogge says. “This is the ultimate limit, you can not get smaller than that.”

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More than 80 years have passed since the German scientist Hans Spemann conducted his famous experiment that laid the foundations for the field of embryonic development. After dividing a salamander embryo in half, Spemann noticed that one half — specifically, the half that gives rise to the salamander’s ‘belly’ (ventral) starts to wither away.

However, the other ‘back’ (dorsal) half that develops into its head, brain and spinal cord, continues to grow, regenerating the missing belly half and develops into a complete, though be it smaller, fully functional embryo.

Spemann then conducted another experiment, where this time, he removed a few cells from the back half of one embryo and transplanted them into the belly half of a different embryo. To his surprise, this gave rise to a Siamese twin embryo where an extra head was generated from the transplanted cells. Moreover, although the resulting embryo was smaller than normal, all its tissues and organs developed in the right proportions irrespective of its size, and functioned properly.

For this work, Spemann received the Nobel Prize in Physiology or Medicine in 1935.

But how does this happen? How exactly is the half embryo able to maintain its tissues and organs in the correct proportions despite being smaller than a normal sized embryo?

Despite many years of research, this question has remained unanswered — until now. More than 80 years since Spemann’s classic experiment, Profs. Naama Barkai, Benny Shilo and research student Danny Ben-Zvi of the Weizmann Institute of Science’s Molecular Genetics Department, together with Prof. Abraham Fainsod of the Hebrew University-Hadassah School of Medicine, Jerusalem, have finally discovered the mechanisms involved.

Previous studies have shown that the growth and development of cells and organs within the embryo is somehow linked to a special group of substances called morphogens. These morphogens are produced in one particular area within the embryo and then spread throughout the entire embryo in varying concentrations. Scientists then began to realize that the fate of embryo cells, that is to say, the type of tissue and organ they are eventually going to develop into, is determined by the concentration of morphogen that they come into contact with. But this information does not answer the specific question as to how proportion is maintained between organs?

The idea for the present research came about when Weizmann Institute scientist Prof. Naama Barkai and her colleagues developed a mathematical model to describe interactions that occur within genetic networks of an embryo.

The data ascertained from this model suggest that the way morphogens spread throughout the embryo in different concentrations is different than previously thought. The team predicts that an inhibitor molecule, which is secreted from a localized source at one side of the embryo and can bind the morphogen, acts as a type of ferry that ’shuttles’ the morphogen to the other side. Therefore, the mathematical model suggests that it is the interactions between the two substances that enable the embryo to keep the relative proportion between organs constant, irrespective of its size. Indeed, these predictions have been validated by experiments conducted on frog embryos by the research team.

The importance of the role of these morphogenic substances, as well as their mechanism of action, is evident by the fact that they have been conserved throughout evolution, where different variants can be found to exist in species ranging from worms to fruit flies and up to higher species including humans. Therefore, understanding the processes that govern embryonic cell development could have many implications. For example, it may lead, in the future, to scientists being able to repair injured tissues.

Prof. Naama Barkai’s research is supported by the Kahn Family Foundation for Humanitarian Support; the Helen and Martin Kimmel Award for Innovative Investigation; the Carolito Stiftung; the Minna James Heineman Stiftung; the PW-Iris Foundation; and the PW-Jani. M Research Fund.

Prof. Benny Shilo’s research is supported by the Y. Leon Benoziyo Institute for Molecular Medicine; the Dr. Josef Cohn Minerva Center for Biomembrane Research; the J & R Center for Scientific Research; the Jeanne and Joseph Nissim Foundation for Life Sciences Research; and the Mary Ralph Designated Philanthropic Fund. Prof. Shilo is the incumbent of the Hilda and Cecil Lewis Professorial Chair in Molecular Genetics.

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Wellcome Trust scientists have identified a key region of the brain which encourages us to be adventurous. The region, located in a primitive area of the brain, is activated when we choose unfamiliar options, suggesting an evolutionary advantage for sampling the unknown. It may also explain why re-branding of familiar products encourages to pick them off the supermarket shelves.

In an experiment carried out at the Wellcome Trust Centre for Neuroimaging at UCL (University College London), volunteers were shown a selection of images, which they had already been familiarised with. Each card had a unique probability of reward attached to it and over the course of the experiment, the volunteers would be able to work out which selection would provide the highest rewards. However, when unfamiliar images were introduced, the researchers found that volunteers were more likely to take a chance and select one of these options than continue with their familiar — and arguably safer — option.

Using fMRI scanners, which measure blood flow in the brain to highlight which areas are most active, Dr Bianca Wittmann and colleagues showed that when the subjects selected an unfamiliar option, an area of the brain known as the ventral striatum lit up, indicating that it was more active. The ventral striatum is in one of the evolutionarily primitive regions of the brain, suggesting that the process can be advantageous and will be shared by many animals.

“Seeking new and unfamiliar experiences is a fundamental behavioural tendency in humans and animals,” says Dr Wittmann. “It makes sense to try new options as they may prove advantageous in the long run. For example, a monkey who chooses to deviate from its diet of bananas, even if this involves moving to an unfamiliar part of the forest and eating a new type of food, may find its diet enriched and more nutritious.”

When we make a particular choice or carry out a particular action which turns out to be beneficial, it is rewarded by a release of neurotransmitters such as dopamine. These rewards help us learn which behaviours are preferable and advantageous and worth repeating. The ventral striatum is one of the key areas involved in processing rewards in the brain. Although the researchers cannot say definitively from the fMRI scans how novelty seeking is being rewarded, Dr Wittmann believes it is likely to be through dopamine release.

However, whilst rewarding the brain for making novel choices may prove advantageous in encouraging us to make potentially beneficial choices, it may also make us more susceptible to exploitation.

“I might have my own favourite choice of chocolate bar, but if I see a different bar repackaged, advertising its ‘new, improved flavour’, my search for novel experiences may encourage me to move away from my usual choice,” says Dr Wittmann. “This introduces the danger of being sold ‘old wine in a new skin’ and is something that marketing departments take advantage of.”

Rewarding the brain for novel choices could have a more serious side effect, argues Professor Nathaniel Daw, now at New York University, who also worked on the study.

“The novelty bonus may be useful in helping us make complex, uncertain decisions, but it clearly has a downside,” says Professor Daw. “In humans, increased novelty-seeking may play a role in gambling and drug addiction, both of which are mediated by malfunctions in dopamine release.”

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