MessageToEagle.com - In a future of quantum computing, data will be treated and transmitted by lasers. The quantum properties of
light will endow machines with gigantic computing potential and an incredible execution rate.
An important discovery - a new way of emitting photons one at a time, with implications for the future of
quantum computing is reported by scientists led by Prof. Anna Fontcuberta i Morral, of the Laboratory of Semiconductor
Materials (LMSC) of Institute of Materials, Ecole Polytechnique Federale de Lausanne, Switzerland.
Scientists have constructed semiconductor nanowires with "quantum dots" of unprecedented quality.
Prof. Moral found that "quantum dots", or nanocrystals, appear naturally on a certain kind of semiconductor
nanowire during their fabrication process.
Nanowires, with a diametre of around a millionth of a millimetre (between 20 and 100 nanometres) are very
efficient at absorbing and manipulating light. By endowing them with nanocrystals or "quantum dots" it is possible
to make them emit unique photons, by charging them with a laser beam of a particular frequency.
The final structure can then emit photos one by one, after having absorbed light.
However, it's only the beginning and still much work remains to be done. At the present time the phenomenon of
the natural creation of dots is not understood by scientists.
In order to exploit the "quantum" potential of light it is necessary, among other things, to be able easily to emit
photons one by one.
The only hitch is that generating quantum dots on a nanowire is notoriously difficult.
The existing methods, which involve the use of a regular modulation of the composition of the nanowire all along its length, are
hard to reproduce and result in strucures with a relatively low output of photons.
Scientists at the LMSC discovered that perfectly functional quantum dots formed "naturally" on the surface
of certain nanowires during the fabrication process.
These dots appeared all by themselves at the interface
between two basic components: Gallium Arsenide (GaAs) and Aluminium Arsenide (AlAs).
"No doubt many scientists working on nanowires have created dots, without realising it," states Anna
Fontcuberta i Morral.
Credit: 2013 EPFL
"The calculations and simulations were carried out on the supercomputers of EPFL by the Laboratory of the
Theory and Simulation of Materials (THEOS) of Nicola Marzari," says Prof. Morral.
As a result, these structures showed a great working stability, which is rare when talking about nanotechnology.
What is more they are hard wearing and very bright, which means that their rate of photon output is incredibly
high. Even better, by controlling the fabrication of the nanowires, the size of the dots can be modulated and
adapted to measure.
Credit: 2013 EPFL
The wavelength of the emitted photons, which is directly dependent on the size of the dots,
can therefore be changed. It is then possible for the nanowire to receive a laser beam of a certain wavelength
or "colour", in order to generate photons of a certain colour - infrared, for example.
"It is also about seeing if it is possible to stimulate dots not only with lasers but electrically, in order to
make them as compatible as we can with all kinds of machine," explains Anna Fontcuberta i Morral.
In a traditional computer, calculations are based on the "bit", which can have one of two values: 0 or 1.
This is the essence of binary language. In a quantum computer the "qbit" (for example a photon) can have
several states at once, states of superposition. It can be either 0 or 1 or both at the same time.
The aim is maintain photons in their state of superposition so that the computer can carry out multiple
calculations in parallel, simultaneously, which will drastically increase the speed of data manipulation.
However this capacity for finding several states at once can not be achieved with a photon unless it is
isolated: sources of unique photons are therefore much sought after.
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MessageToEagle.com - In a future of quantum computing, data will be treated and transmitted by lasers. The quantum properties of
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