Can a Human See a Single Photon? (1996)

Post by abdullahkhalids » Fri, Jan 20, 2023, 11:28 PM UTC

abdullahkhalids wrote: post #122

xhrpost wrote: post #106

Earlier quoted context omitted.

> To optimize this ratio in practice, we used the multi-pixel sensor of an electron multiplying charge-coupled device (EMCCD) camera as our idler detector (Fig. 1a). As the EMCCD can detect multiple photons simultaneously, it allowed us to identify and reject, that is, post-select, all events other than those where a single-photon pair was generated with a higher efficiency than with more traditional single-photon av…

There is a process called spontaneous parametric downconversion (SPDC), where if you shine laser of frequency f at a crystal, it will with small probability p emit two photons of frequency f/2 (energy conservation in play here). If done correctly, the outgoing laser light and the two photons all travel in different directions and so can be separated and further directed using mirrors or optical fiber cables. Because…

                                        +---------------------+
                                        | Heralding detector  |
                                        |                     |
                                        +---------------------+
                                       /
                                      /
                       +----------+  /  Photon 1
                       |          | /
    Laser beam ------> | Crystal  | ------------> Outgoing laser beam
                       |          | \
                       +----------+  \ Photon 2
                                      \
                                       \
                                        To human eye

Post by d_tr » Fri, Jan 20, 2023, 11:40 PM UTC

HPsquared wrote: post #110

d_tr wrote: post #49

Earlier quoted context omitted.

> Is the back of an eye a sufficient observer? :) It definitely is. The retina "measures" photon positions, which is why you see images. Observation is just interaction, no need to consider whether A can observe B. If they interact, some kind of observation takes place.

When the photon passes through the lens and the watery liquid part, its path is bent by refraction. Does that process also count as an "interaction", or is that different to what happens when the photon hits the retina?

Post by tshaddox » Sat, Jan 21, 2023, 1:41 AM UTC

photochemsyn wrote: post #64

lebubule wrote: post #15

Recent experiments have put the claim to test Overview https://www.nature.com/articles/nature.2016.20282 The actual work https://www.nature.com/articles/ncomms12172 > Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance.

Interesting study, though if you look at the results 'significantly above chance' looks to be 0.60 +/- .05, which is indeed better than 0.50 but not what anyone could call reliable detection. I wonder if trained owls could detect single photons, or if their night vision is based on just having much larger lenses that collect more light? It seems that all rods in retinas are activated by single-photon-absorption, it's…

Post by BlueTemplar » Sat, Jan 21, 2023, 2:24 AM UTC

somat wrote: post #61

superposeur wrote: post #6

I’ve been aware of this fact as Feynman points it out in the course of the lectures, but find it totally nuts — there is some sense of scale I’m missing. Matter consists of discrete chunks, atoms, but these chunks are so infinitesimal and numerous that there is no question of seeing them and any effect involving a handful of them is far, far below the human scale. Light also comes in chunks, and the number of these c…

I am not a physicist but fun fact, In transit there is no such thing as a photon(electro magnetic waves can transit at any energy level) however light can only interact with matter at discrete energy levels, so the photon(a discrete energy level of light) only exists there, at the interaction with matter. For some very good practical optics you can do a lot worse than the Huygens Optics youtube channel. https://www.y…

Post by jiveturkey » Sat, Jan 21, 2023, 9:10 PM UTC

sandworm101 wrote: post #70

danbruc wrote: post #34

On a related note, you can hear sounds that displace your eardrums on the order of an atomic diameter. At least that is something I heard years ago, a quick search turned up this StackExchange question [1] so there may be some truth to this, I did however not read the answers too carefully. They actually seems to suggest that the threshold is even quite a bit smaller which makes me somewhat cautious of the claim, but…

>> sounds that displace your eardrums on the order of an atomic diameter. That isn't all that surprising really. This isn't one atom moving a tiny bit. It is billions and billions of atoms all shifting back and forth together.