En busca del circuito integrado óptico/Searching for an optical integrated circuit

Hoy día, Internet y los ordenadores necesitab ser cada vez más rápidos y más potentes. Sin embargo, las CPU's convencionales limitan el rendimiento de los ordenadores, por ejempo, al producir una enorme cantidad de calor. La causa de ésto son los millones de transistores que conmutan o amplifican las señales electrónicass en las CPU's: un centímetro cuadrado de CPU puede emitir hasta 125 watios de calor, es decir diez veces más que un centímetro cuadrado de una estufa eléctrica.
Por esto, los científicos llevan mucho tiempo intentando producir circuitos integrados que operen con fotones en lugar de electrones. La razón es que los fotones no solo generan mucho menos calor que los electrones, sino que también permiten transferir datos a mayor velocidad.
El grupo de investigación liderado por Vahid Sandoghdar, Profesor del Laboratorio de Química-Física del Instituto Suizo Tecnológico de Zurich, ha hecho un avance decisivo al crear un transistor óptico con una única molécula.
Para ello se aprovecha el hecho de que la energía de la molécula está cuantizada: cuando la luz del láser golpea una molécula que está en su estado fundamental, la luz es absorbida. A la inversa, es posible liberar la energía absorbida con un segundo rayo láser. Esto sucede porque el rayo cambia el estado cuántico de la molécula, con el resultado de que la luz del del segundo rayo es amplificada.
Según Jaesuk Hwang, primer autor del estudio, “la amplificación de un láser convencional puede hacerse con un número enorme de moléculas”. Sin embargo, los científicos de Zurich han conseguido producir amplificación estimulada con una única molécula. Para ellos han necesitado enfriarla a menos 272 grados centígrados, es decir 1 grado por encima del cero absoluto.
Utilizando un rayo láser para preparar el estado cuántico de una única molécula de forma controladad, los científicos pueden atenuar o amplificar simultáneamente un segundo rayo láser, una forma de operar idéntica a la de un transistor convencional. Estos componentes podrían preparar el camino para un fuuro ordenador cuántico.

Internet connections and computers need to be ever faster and more powerful nowadays. However, conventional central processing units (CPUs) limit the performance of computers, for example because they produce an enormous amount of heat. The millions of transistors that switch and amplify the electronic signals in the CPUs are responsible for this. One square centimeter of CPU can emit up to 125 watts of heat, which is more than ten times as much as a square centimeter of an electric hotplate.
This is why scientists have been trying for some time to find ways to produce integrated circuits that operate on the basis of photons instead of electrons. The reason is that photons do not only generate much less heat than electrons, but they also enable considerably higher data transfer rates.
The research group led by Vahid Sandoghdar, Professor at the Laboratory of Physical Chemistry of ETH Zurich, has now achieved a decisive breakthrough by successfully creating an optical transistor with a single molecule.
For this, they have made use of the fact that a molecule’s energy is quantized: when laser light strikes a molecule that is in its ground state, the light is absorbed. Conversely, it is possible to release the absorbed energy again in a targeted way with a second light beam. This occurs because the beam changes the molecule’s quantum state, with the result that the light beam is amplified.
According to Jaesuk Hwang, first author of the study, “amplification in a conventional laser is achieved by an enormous number of molecules”. However, the ETH Zurich scientists have now been able to generate stimulated emission using just one molecule. The researchers therefore needed to cool the molecule down to minus 272 degrees Celsius, i.e. one degree above absolute zero.
By using one laser beam to prepare the quantum state of a single molecule in a controlled fashion, scientists could significantly attenuate or amplify a second laser beam. This mode of operation is identical to that of a conventional transistor. Thus component parts such as the new single molecule transistor may also pave the way for a quantum computer.

Tomado de/Taken from ETH Zurich

Resumen de la publicación/Abstract of the research paper
A single-molecule optical transistor
J. Hwang, M. Pototschnig, R. Lettow, G. Zumofen, A. Renn, S. Götzinger & V. Sandoghdar
Nature 460, 76-80 (2 July 2009) doi:10.1038/nature08134
The transistor is one of the most influential inventions of modern times and is ubiquitous in present-day technologies. In the continuing development of increasingly powerful computers as well as alternative technologies based on the prospects of quantum information processing, switching and amplification functionalities are being sought in ultrasmall objects, such as nanotubes, molecules or atoms. Among the possible choices of signal carriers, photons are particularly attractive because of their robustness against decoherence, but their control at the nanometre scale poses a significant challenge as conventional nonlinear materials become ineffective. To remedy this shortcoming, resonances in optical emitters can be exploited, and atomic ensembles have been successfully used to mediate weak light beams7. However, single-emitter manipulation of photonic signals has remained elusive and has only been studied in high-finesse microcavities or waveguides. Here we demonstrate that a single dye molecule can operate as an optical transistor and coherently attenuate or amplify a tightly focused laser beam, depending on the power of a second 'gating' beam that controls the degree of population inversion. Such a quantum optical transistor has also the potential for manipulating non-classical light fields down to the single-photon level. We discuss some of the hurdles along the road towards practical implementations, and their possible solutions.