Traffic rules for spontaneous emissions

Experimental breakthrough in quantum optics

Apparently, it has been possible to influence the light emission in the decay of individual quantum emissions (quantum dots). The materials used can be thought of applications in miniature lasers, sun racks or future quantum computers.

The coincidence plays a fundamental role in quantum mechanics. Is Z. B. An atom in an excited state of energy, for example because it is part of a hot gas, will give it its energy in the form of radiation again, as a Package (Photon with appropriate frequency). But when?

Emitting atom

There is only one statistical statement: After a certain time, the half of the excited atoms have emitted light – one speaks of the life of the excited state. For the individual atom, however, you can not make a prediction at all – that’s why one speaks of spontaneous emissions.

The deeper cause for the randomness of the emission time is the physically speaking, "disarray" surroundings. Normally she preferably prefer no light frequency, but let all equally. If the atom is put into a chamber with reflective, things look different. If the emission frequency corresponds to the resonant frequency of the chamber, the life of the excitation is tangled, the radiation is stronged.

The optical properties of photonic crystals correspond to those of mother of pearl or the edition on butterfly flights. Gross. 2 mm.

1987 postulated Eli Yablonovitch (then Bell Telephone Co., now UCLA) and John Sajeev from the Princeton University independent of each other that appropriately produced crystals, actually structures made of refractory material with inconspicuous, in roughly regular cavity, for light of certain wavelength had to be completely immailing, while they were otherwise translucent. The dream of "Optical semiconductor" proved to be a strong motivation, and in 1992 the first "photonic crystal" manufactured.

Experiment and results

Peter Lodahl and his team from the University of Twente, Enschede publishers now in Nature (Vol. 430, 5 August 2004), how they used photonic crystals to influence the lifetime of excited quantum material. They placed a number of so-called "Inverse opals" in principle through and by porose blocks from titanium dioxide (TiO2), you know it from the paint box: a covering woman), with tetrahedrically arranged cavity. Think of a box full of billiard balls, regularly arranged, and then replace material and air …

The diameter of the cavity was 370 nanometers (millionths of millimeters, nm) in the narrowest grid and 580 nm farthest. It was embedded in the emitters, small balls from the semiconductor Cadmium Selenid (CDSE), diameter in the smallest case 3.8 nm, up to 6 nm. The cadmium selenide balls behave like Quantum Dots: they have a ground state and an excited state (modeling a 2-level system) and emit a photon of the corresponding frequency when decaying the excited state. The excitation happens by means of laser light. As a reference for emission behavior, massive TiO2 blocks were doped with the quantum dots – as a homogeneous environment they do not prefer frequencies or directions.

Electron microscopic image of one of the photonic crystals used

The behavior of the Quantum Dots doubled now derive from the coarse ratios. Compared to the reference, for certain combinations of emitter grooves and lattice width resulted in a lifespan of life and emission of 50%, in other combinations a shift of 30% (with appropriate lengthening of life). In contrast to the above-mentioned example with the atom in the resonator, the effect is much broadband, and of course the effort is unevenly smaller – everything takes place at room temperature, under normal prere and with FURS Blobe Eye visible objects. Decisive for further development is that the data found can be explained by the theoretical model and the effect is obviously well understood.

How could it continue

Photonics, the technological counterpuck on electronics, is now dealing with a wide variety of applications of photonic crystals:

  1. When taking advantage of the emission, more effective solar cells can think of less losses between collecting and removing the irradiated energy.

Even more important are the applications for telecommunications and the IT:

  1. It was able to build photonic crystals made of semiconductor material – integrated circuits connecting electrical and optical effects for most absorbest miniaturization.
  2. The construction of miniaturized lasers was able to benefit from the scanning of the emission, Z. B. For optical storage media.
  3. An interesting application would be an optimized one-photon source emitted in a variety of regularly diminishes, D. H. After stimulating reliable in a short period of time (quantum computing, quantum cryptography).
  4. And of course, the use of photonic crystals as storage and printed circuit blocks can be speculated in a quantum computer – not that it lacked in this regard. The special charm of this path is that the material properties even take control of the quantum effects, with relatively simple production and in principle unproblematic deployment.
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