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.