Question about this quantum dot experiment:

http://phys.org/news/2016-06-path-quantum-dots-electrically-controlled-cavities.html#nRlv

It said previous efforts had photon's with 1/20th the intensity of the ones from the latest experiment.

If they are talking about individual photons, wouldn't the energy of any photon of a given wavelength be the same? say a 400 NM photon, another 400 would be exactly the same energy per photon.

So when they say one is stronger than the other, they are talking about absolute numbers of photons, not the energy of a single photon of X wavelength, right?

Originally posted by sonhouse
http://phys.org/news/2016-06-path-quantum-dots-electrically-controlled-cavities.html#nRlv

It said previous efforts had photon's with 1/20th the intensity of the ones from the latest experiment.

If they are talking about individual photons, wouldn't the energy of any photon of a given wavelength be the same? say a 400 NM photon, another 400 would be ex ...[text shortened]... ing about absolute numbers of photons, not the energy of a single photon of X wavelength, right?

It's a little unclear from the article. According to the Wikipedia page on brightness it is a subjective thing, it is the perception of luminance and often (incorrectly) used to mean that. This would make sense because the probability of the emitted photon interacting with a photon detector depends on the wavefunction overlap (how much of the photon's wavefunction overlaps with the detectors electron's wavefunction). The group were trying to produce highly directional photons, so the wavefunction overlap will be greater and so the photon will have a higher chance of interacting with the detector than a spherically symmetric wave would. So I think that the source is brighter in the way a torch with a reflector is brighter than a torch with the reflector removed - it's not that the bulb is emitting more energy, it's just that more of it is going in a useful direction.

Originally posted by DeepThought
It's a little unclear from the article. According to the Wikipedia page on brightness it is a subjective thing, it is the perception of luminance and often (incorrectly) used to mean that. This would make sense because the probability of the emitted photon interacting with a photon detector depends on the wavefunction overlap (how much of the photon's ...[text shortened]... that the bulb is emitting more energy, it's just that more of it is going in a useful direction.

Which would be a function of multiple photons, not an individual photon I would assume.

Originally posted by sonhouse
Which would be a function of multiple photons, not an individual photon I would assume.

I'm not quite sure what you mean by that, so to be sure I'll cover both bases.

According to the article it's a single photon effect. By brightness they mean something like cross-section. They can produce a directional beam with a single photon. At the one particle level the "Schrodinger" equation is the wave equation one gets from Maxwell's equations - all quantum mechanics adds is the relation between energy and frequency. This changes if we allow for interactions or very high energies - the coupling depends on the energy scale which is something you need a particle accelerator to notice and photons with an energy of more than about 1MeV can become an electron-positron pair - but in this very low energy (~1eV) single particle setting we can safely ignore that. So apart from the amplitude having to give a probability of one of the photon existing the classical field and the photon wave function are the same, provided there is only one photon. This directionality at the individual photon level causes the detector to be more likely to detect the incoming photon.

Their thing emits one photon at a time. I assume they did a series of trials and measured the number of times they detected the photon coming out in the right direction, and used that as a measure of brightness. So if that was what you meant I think you're right.