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A visualization of the molecule. The triangular depression on the bottom right represents the arsenic atom. The dots in the center saucer are bonding locations for a single electron. The yellow dots in the upper left center are bonding locations in which the electron is in a quantum state.  (Source: Purdue University image/David Ebert)
Nanoelectronics researchers discover a bizarre shaped molecule in one of their devices can act as first known quantum state-manipulable atom

Imagine a tiny arsenic atom embedded in a tiny strip of silicon atoms.  An electric current is applied.  Something strange arises on the surface -- an exotic molecule.  On one end is the spherical submerged arsenic atom; on the other end is an "artificial" flat atom, seemingly 2D, created as an artifact.  The pair form an exotic molecule, which has a shared electron, which can be manipulated to be at either end, or in an intermediate quantum state.

Thus arose one of the most confusing, most promising, and strangest breakthroughs in the newly formed field of quantum computing. 

Quantum computing is the term referring to a unique type of computing that takes advantage of physics phenomena on a very small subatomic scale.  Whereas a traditional computer works in bits -- 1s and 0s, which represent the presence or absence of groups of electrons -- a quantum computer use qubits -- multi-state units based on the position and characteristics of a single electron.  A single qubit can encode far more information leading to faster, smaller computers.

Imagine a census computer.  In a modern computer, information would be stored across trillions of bits, encoding the person's name, address, and status.  In a quantum computer this same information could be stored across a much smaller handful of bits.  The computer could "see" multiple people's information simultaneously, allowing for instant processing of vast amounts of data and easier searches.

Further quantum computing looks to exploit other unusual physical phenomena such as entanglement, which allows two atoms at a distance to instantly communicate.  Such communication could be faster than light without violating relativity.

In order to construct a full quantum computer, you must have an atom or molecule capable of containing multiple quantum states.  Formerly, such a manipulable molecule remained undiscovered, but with the discovery of the exotic compound, quantum computing hopes are invigorated.

Gerhard Klimeck, professor of electrical and computer engineering at Purdue University and associate director for technology for the national Network for Computational Nanotechnology remarked, "Up to now large-scale quantum computing has been a dream.  This development may not bring us a quantum computer 10 years faster, but our dreams about these machines are now more realistic."

He continued, "If you want to build a quantum computer you have to be able to control the occupancy of the quantum states.  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 new molecule was first discovered by Sven Rogge and his colleagues at Delft University of Technology in the Netherlands.  His team was experimenting on impurities in nano-scale transistors.  They found that a single atom was transporting electrons, but could not find the impurity responsible.  It turned out it was not an impurity, but a synthetic atom with an unknown proton/neutron character, created by the electrical current.  The exotic atom was flat and formed a molecule with an arsenic atom on the transistor.

Much of this picture only became clear thanks to the work of physicist Lloyd Hollenberg and colleagues at the University of Melbourne in Australia who helped to explain the molecule's strange behavior and appearance.

Hollenberg explained, "The team found that the measurements only made sense if the molecule was considered to be made of two parts.  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, and graduate student Rajib Rahman used the analysis to develop a three million-atom model in nano-electronics modeling program NEMO 3-D to analyze the behavior.  From this, they determined that the exotic flat atom represented a controllable quantum state atom, via its electron.  The quantum state was voltage dependent, the necessary characteristic for an electricity-based quantum computer.

Last David Ebert, a professor of electrical and computer engineering at Purdue, and graduate student Insoo Woo, helped transform the model into an image to help visualize the discovery.

Delft's Rogge, the first of the discoverers stated, "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.  This is the ultimate limit, you cannot get smaller than that."

The breakthrough, like many historic ones (such as the discovery of Penicillin), was largely accidental.  And it is extremely fortunate, in that it may one day allow complex, incredibly powerful quantum computers to become reality and solve many complex sets of problems.





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