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Superradiance: Quantum Effect Detected in Tiny Diamonds:
"Superradiance" is the phenomenon of one atom giving off energy in the form of light and causing a large number of other atoms in its immediate vicinity to emit energy as well at the same time. This creates a short, intense flash of light.
Up until now, this phenomenon could only be studied with free atoms (and with the use of special symmetries). Now, at TU Wien (Vienna), it was measured in a solid-state system. The team used nitrogen atoms, built into tiny diamonds that can be coupled with microwave radiation. The results have now been published in the journal Nature Physics.
[...] "When the atom absorbs energy, it is shifted into a so-called excited state. When it returns to a lower energy state, the energy is released again in the form of a photon. This usually happens randomly, at completely unpredictable points in time," says Johannes Majer[...]. However, if several atoms are located close to each other, an interesting quantum effect can occur: one of the atoms emits a photon (spontaneously and randomly), thereby affecting all other excited atoms in its neighborhood. Many of them release their excess energy at the same moment, producing an intense flash of quantum light. This phenomenon is called "superradiance."
"Unfortunately, this effect cannot be directly observed with ordinary atoms," says Andreas Angerer, first author of the study. "Super radiance is only possible if you place all the atoms in an area that is significantly smaller than the wavelength of the photons." So you would have to focus the atoms to less than 100 nanometers -- and then, the interactions between the atoms would be so strong that the effect would no longer be possible.
One solution to this problem is using a quantum system that Majer and his team have been researching for years: tiny defects built into diamonds. While ordinary diamonds consist of a regular grid of carbon atoms, lattice defects have been deliberately incorporated into the diamonds in Majer's lab. At certain points, instead of a carbon atom, there is a nitrogen atom, and the adjacent point in the diamond lattice is unoccupied.
[...] Just like ordinary atoms, these diamond defects can also be switched into an excited state -- but this is achieved with photons in the microwave range, with a very large wavelength. "Our system has the decisive advantage that we can work with electromagnetic radiation that has a wavelength of several centimeters -- so it is no problem to concentrate the individual defect sites within the radius of one wavelength," explains Andreas Angerer.
(Score: 5, Informative) by Anonymous Coward on Thursday September 06 2018, @04:55AM (1 child)
It's clear from my fellow soylentils comments that you don't understand what's going on here so allow me to explain.
They mention microwaves, but let's think in terms of visible light because it's a bit easier to imagine.
What they are saying is that if you pack a group of atoms in together and that total packing is the wavelength of a given photon, then you shoot a photon in there, all the atoms will all give off a photon at the same time.
This seems to violate conservation of energy but it's only because you're assuming the photon coming out is somehow being multiplied. It isn't, it's brand new photon.
Let's assume a crystal containing 10 nitrogen atoms packed into a lattice of 75nm. This is the wavelength of high intensity UV and you could do this with current lithography techniques.
They are tightly packed, but only 1 atom can absorb the photon, this atom gets an electron kicked up into a higher orbital.
As it's being boosted, the energy travels to the other 10 atoms and is distributed, instantly because they are so close together that from the perspective of the photon, they are all the same atom.
At some point the excited electron tunnels back to ground.
When it does this, the other electrons around the other atoms do so at the same time.
What is emitted though are 10 photons at a wavelength of 750nm, which is the far end of visible red but not quite infrared.
The interesting thing about this is that these photons ought to be colimated (laser) and they ought to be entangled.
So in a nutshell this isn't playing billiards, it's dropping a rock in a still pool and watching the waves lap against the sides of the pool.
(Score: 2) by PinkyGigglebrain on Thursday September 06 2018, @06:07AM
Thank you. This explanation made sense, explained what the big deal was about this story, and how Superradiance is different than what happens in a LASER.
I hope someone with mod points can give your comment the +5 Informative it deserves.
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."