A universal quantum computer still is a vision. Special quantum
systems that promise to solve certain tasks more quickly than a
classical computer, however, are already playing an important role in
science. To reliably find a certain element in unsorted data, a
conventional computer has to run through all search elements
successively in the most unfavorable case. A quantum system with an
implemented Grover's search algorithm quadratically accelerates search.
Research teams headed by Professors Wolfgang Wernsdorfer and Mario
Ruben of KIT, together with scientists of the Institut Néel (Grenoble),
have succeeded in doing this: The scientists applied Grover's algorithm
to a molecular magnet and, thus, created a quantum system, whose task is
the rapid finding of search elements in unsorted data.
In their latest research project, they demonstrated feasibility of a
quick search for a small database of four elements. "But this method can
be implemented in any quantum system with many, non-equidistant energy
levels, which opens up the way towards a universal quantum search
algorithm," Professor Ruben says.
The scientists implemented Grover's algorithm in a molecular magnet
that was subjected to superposition with specially designed microwaves.
Superposition is a quantum effect, in which a particle assumes different
states at the same time. Upon execution of the quantum operations, a
single-molecule transistor read out the search results. An animation
illustrates this process.
Wolfgang Wernsdorfer, Professor of KIT's Physikalisches Institut and
Institute of Nanotechnology (INT), emphasizes that the quantum states
were manipulated at very low temperatures using electric fields
exclusively. "That is why we hope that this technology can be integrated
into current electronic devices," Wernsdorfer adds.
The customized molecule transistor was synthesized by Mario Ruben's
team at INT and KIT's Institute for Inorganic Chemistry. In its center, a
terbium atom with a pronounced magnetic moment, a spin, is located. The
terbium is surrounded by organic molecules that shield it against
external impacts.
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