1

Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 08/05/2021 05:07:25 »

Indeed, it shows to be careful about the basic quantum idealization of wavefunction collapse being instant - they have some hidden dynamics we should search for ... like EM wave of single photon being produced by electron dynamics - such photon carries energy difference and angular momentum (orbital or spin) of electron.

~1000 articles citing 2010 Science "Delay in photoemission": https://scholar.google.pl/scholar?cites=15193546925951882986&as_sdt=2005&sciodt=0,5&hl=en
E.g. 2020 "Probing molecular environment through photoemission delays" https://www.nature.com/articles/s41567-020-0887-8

Attosecond chronoscopy has revealed small but measurable delays in photoionization, characterized by the ejection of an electron on absorption of a single photon. Ionization-delay measurements in atomic targets provide a wealth of information about the  timing  of  the  photoelectric  effect,  resonances,  electron  correlations  and  transport.

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 08/05/2021 04:21:15 »

Regarding plane waves, shape of wind, there are EM waves also of huge sizes (e.g. https://en.wikipedia.org/wiki/Extremely_low_frequency ).
However, optical photons are very special type: e.g. produced by concrete deexciting atom, then distance/c later absorbed by another concrete atom.

There are observed delays in atomic processes, like ~21 attosecod delay in photoemission ( https://science.sciencemag.org/content/328/5986/1658 ) - EM radiation, being mainly response to electron dynamics, propagates ~6nm during this time.
So what exactly happens during such 21as of production of EM field of single optical photon?

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 07/05/2021 03:23:42 »

There is both EM wave governed by Maxwell equations, and quantum amplitude governed e.g. by Schrodinger -  "pilot" wave for psi=sqrt(rho) exp(-iS/hbar) Madelung substitution( https://en.wikipedia.org/wiki/Pilot_wave_theory#Mathematical_formulation_for_a_single_particle ).
For let say Mach-Zehnder interference, there is no doubts that "pilot" wave of quantum amplitudes propagates through both trajectories.

However, the question is about corpuscular part of wave-particle duality, does it also propagate through both trajectories, or maybe only through one like in this diagram (from http://redshift.vif.com/JournalFiles/V16NO2PDF/V16N2CRO.pdf ):


In case of interference of electron, it is elementary charge - cannot split in two, in experiments it is always nearly point-like charge ... also, scenarios with electron going through lower or upper arm differ by electric field around such setting influencing surrounding atoms - they are very different.
For single photons, there are e.g. these experiments measuring averaged trajectories of interfering photons: https://science.sciencemag.org/content/332/6034/1170.full


There are also experiments being able to use both wave and particle part of duality simultaneously, e.g. https://en.wikipedia.org/wiki/Afshar_experiment

So while quantum amplitude of single photon: the wave part of wave-particle duality seems to form e.g. plane waves, the corpuscular part seems to travel through a concrete trajectory (e.g. from the screen to our eyes).

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 06/05/2021 18:37:50 »

Sure very narrow in momentum spectrum, but rather nonzero: not a plane wave ... hard to imagine e.g. that photons going from screen to our eyes are plane waves (?)
If not zero, so what more specific can we tell about it?  (is this question of this thread)

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 06/05/2021 17:37:47 »

Size of photon makes sense also in QM: e.g. as width of wavepacket ( https://en.wikipedia.org/wiki/Wave_packet ), as uncertainty of quantum position operator, through adding terms in WKB approximation ( https://en.wikipedia.org/wiki/WKB_approximation ) etc.

So please elaborate what do you know about this basic question? (beside excuses)

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 06/05/2021 10:48:44 »

We know photon is EM wave - also from quantum perspective, it means e.g. ensemble of EM field configurations, wavepacket - we should know at least some its basic properties like size e.g. as uncertainty of position operator for such wavepacket.

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 06/05/2021 09:29:36 »

"The size and shape of single photon" http://dx.doi.org/10.4236/oalib.1107179 has nice looking models of photon:



The big question is how true they are???
Sadly, while many claim that physics is nearly solved, we know nearly nothing about such basic questions like EM field configuration and dynamics of photon (wavepacket) ...

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 30/04/2021 19:35:57 »

Sure, the energy density of EM field of a photon might resemble ellipsoid as containing most of it hv energy, but there might be also some tail for the remaining part of energy.
Also, such hole is rather made of matter - leading to complex interactions with its orbitals, which might be difficult to properly interprete.

But generally I would indeed expect a gradual reduce of intensity for hole size at scale of wavelength - the first paper suggests wavelength/pi, e.g. based on microscope resolution:

the resolving power of a microscope (with monochromatic light) being  “a little less than a third of the wavelength”; λ/π is 5% less than λ/3, [12];

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Physics, Astronomy & Cosmology / Re: What is the size and shape of single optical photon?

« on: 30/04/2021 11:04:21 »

There should be some concrete evolution of EM field for single photon, having rho~|E|^2+|B|^2 energy density.

While it is a difficult question, we should at least try to know the basics like approximate size - and the two mentioned articles try to do it, most importantly discuss experimental arguments.
If not having anything better, we can start with discussing them - so what do you think e.g. about the experimental arguments quoted in the first post here? Are there any other?

For example, I remember there was argument that in Mach-Zehnder if we introduce ~1 period delay in one arm, we lose interference for single photons ... can anybody point some reference for that?

So I suggest that, if they have the right polarization, photons can fit through a long, narrow gap with a width much smaller than a wavelength.

Indeed this would interesting to check - maybe there are this kind of papers?

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Physics, Astronomy & Cosmology / What is the size and shape of single optical photon?

« on: 30/04/2021 05:23:37 »

Optical photon is produced e.g. during deexcitation of atom, carrying energy, momentum and angular momentum difference.
So how is this energy distributed in space - what is the shape and size of single photon?

Looking for literature, I have found started by Geoffrey Hunter, here is one of articles: "Einstein’s Photon Concept Quantified by the Bohr Model of the Photon" https://arxiv.org/pdf/quant-ph/0506231.pdf

Most importantly, he claims that such single optical photon has shape similar to elongated ellipsoid of length being wavelength λ, and diameter λ/π (?), providing reasonably looking arguments:

1) Its length of λ is confirmed by:

– the generation of laser pulses that are just a few periods long;
– for the radiation from an atom to be monochromatic (as observed), the emission must take place within one period [10];
– the sub-picosecond response time of the photoelectric effect [11];

2) The diameter of λ/π is confirmed by:

– he attenuation of direct (undiffracted) transmission of circularly polarized light through slits narrower than λ/π: our own measurements of the effective diameter of microwaves [8,p.166] confirmed this within the experimental error of 0.5%;
– the resolving power of a microscope (with monochromatic light) being  “a little less than a third of the wavelength”; λ/π is 5% less than λ/3, [12];

Is it the proper answer?
Are there other reasonable answers, experimental arguments?

Updates: Paper by different author: https://arxiv.org/pdf/1604.03869

the length of a photon is half of the wave length, and the radius is proportional to square root of the wavelength

2021 "The size and shape of single photon" http://dx.doi.org/10.4236/oalib.1107179
Related: https://physics.stackexchange.com/questions/612110/is-it-possible-to-confine-a-photon-in-less-than-its-wavelength

Here is some paper trying to model emission of photon from hydrogen: https://link.springer.com/chapter/10.1007/0-306-48052-2_20

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Question of the Week / Re: QotW - 21.04.19 - How do zip files work?

« on: 28/04/2021 20:36:35 »

Small update:
Instead of ancient zip, now your files are often written with modern zstd: 2-5x faster, better compression, e.g. in Linux kernel and products of hundreds of companies: https://en.wikipedia.org/wiki/Zstandard
On Apple with LZFSE: https://en.wikipedia.org/wiki/LZFSE
For DNA compression nearly default is CRAM: https://en.wikipedia.org/wiki/CRAM_(file_format)
In the next months JPEG(, GIF, PNG) should be successfully replaced with fresh JPEG XL - 3x smaller photos and many missing features: https://en.wikipedia.org/wiki/JPEG_XL

In place of Huffman coding (only complete bits), all the above use ANS (handling fractional bits): https://en.wikipedia.org/wiki/Asymmetric_numeral_systems

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Physics, Astronomy & Cosmology / Re: Is time travel possible?

« on: 05/04/2021 09:51:17 »

While it is highly nonintuitive for us, there are lots of arguments for living in spacetime, time being only 4th dimension, fundamentally there it time/CPT symmetry, e.g.:
- in special relativity we literally change time direction by changing velocity,
- general relativity discusses behavior of entire 4D spacetime as kind of "4D jello",
- there are lots of arguments for time symmetry in quantum mechanics, e.g. path ensembles, unitary evolution, Wheeler, delayed choice experiments ... Bell violation: of inequalities derived assuming time asymmetry (hidden variables in the past) - no problem to violate them in symmetric models starting with Ising ( https://physics.stackexchange.com/questions/524856/violation-of-bell-like-inequalities-with-spatial-boltzmann-path-ensemble-ising ).

Talk with discussion and gathered experiments like Wheeler, delayed choice quantum eraser etc.:

Regarding free will, in spacetime "the future is already there" based also on our decisions ... which from our perspective were made by us - perspective with limited knowledge: "physics knows the future", but we don't - we are systems of atoms ruled by the same physics, making decisions based on our history, knowledge and current situation.

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Physics, Astronomy & Cosmology / Re: Is time travel possible?

« on: 01/04/2021 11:14:38 »

We live in 4D spacetime - time is just 4th dimension, past and future are already there: https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)
The question is if causality works in both time directions, and CPT theorem ( https://en.wikipedia.org/wiki/CPT_symmetry ) suggests that it should ... ?

For example laser stimulates photon emission, which cause target excitation later.
So could there be built CPT analogue of laser? Stimulating photon absorption - causing deexcitation of target earlier?

For FEL ( https://en.wikipedia.org/wiki/Free-electron_laser ) it seems doable: electrons in sinus-like trajectories, so after CPT we get just positrons traveling the same trajectories in opposite direction.
So could it cause e.g. faster deexcitation of constantly excited target (e.g. sodium lamp for narrow spectrum)?

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Physics, Astronomy & Cosmology / Re: Similarity between particle physics and superfluid e.g. fluxons?

« on: 10/03/2021 05:20:33 »

There are more long-range interactions for topological solitons in liquid crystals, e.g.:
- Coulomb: "Coulomb-like interaction in nematic emulsions induced by external torques exerted on the colloids" https://journals.aps.org/pre/abstract/10.1103/PhysRevE.76.011707
- dipole-dipole: "Novel Colloidal Interactions in Anisotropic Fluids" https://science.sciencemag.org/content/275/5307/1770
- quardupole-quadrupole: "Long-range forces and aggregation of colloid particles in a nematic liquid crystal": https://journals.aps.org/pre/abstract/10.1103/PhysRevE.55.2958



Skyrme models are for strong interaction ... so why can't we model all?

These liquid crystal systems are for uniaxial nematic - one distinguished axis everywhere ... bringing a question about natural generalization: biaxial nematic: 3 distinguished axes in 3D (4 in spacetime adds gravity) - giving particle-like configurations resembling 3 leptons, neutrinos, baryons, nuclei ...

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Physics, Astronomy & Cosmology / Re: Similarity between particle physics and superfluid e.g. fluxons?

« on: 04/03/2021 09:53:12 »

Very nice paper with observed particle-like topological configurations in liquid crystal:

"Annihilation dynamics of topological defects induced by microparticles in nematic liquid crystals": https://pubs.rsc.org/en/content/articlelanding/2019/sm/c9sm01710k#!divAbstract

There is also long-range interaction: F ~ charge1*charge2/D Coulomb-like formula (1.2) below:



ps. This discussion has developed in https://www.scienceforums.net/topic/124416-similarity-between-particle-physics-and-macroscopic-quantum-phenomena-like-fluxons/

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Physics, Astronomy & Cosmology / Re: Similarity between particle physics and superfluid e.g. fluxons?

« on: 26/02/2021 11:50:51 »

There is a growing society of physicists going in this direction, e.g. here are lots of interesting talks for example toward such models of nuclei: http://solitonsatwork.net/?display=archive
Basic book: http://www.lmpt.univ-tours.fr/~volkov/Manton-Sutcliffe.pdf
Some recent liquid crystal experimental paper: https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-8-2-255&id=447762

Models of nuclei from https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.232002


ps. Nice mechanical realization of 1D topological solitons - both moving and traveling, with pair creation/annihilation:

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Physics, Astronomy & Cosmology / Re: Similarity between particle physics and superfluid e.g. fluxons?

« on: 18/02/2021 08:24:09 »

Let me take a bit further this analogy (can much further) - in superfluid biaxial nematic we would also need 1D fluxon-like configuration - along one of 3 distinguishable axes.
Such fluxons can e.g. form a short loop of one of 3 types - which should have much lower mass/energy than charge, be stable and extremely difficult to interact with, can transform between 3 types with internal rotation ... don't they resemble 3 neutrinos and https://en.wikipedia.org/wiki/Neutrino_oscillation ?

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Physics, Astronomy & Cosmology / Similarity between particle physics and superfluid e.g. fluxons?

« on: 07/02/2021 08:29:37 »

Especially in superconductors/superfluids there are observed so called macroscopic quantum phenomena ( https://en.wikipedia.org/wiki/Macroscopic_quantum_phenomena ) - stable constructs like fluxon/Abrikosov vortex quantizing magnetic field due to toplogical constraints.
There is observed e.g. interference ( https://journals.aps.org/prb/abstract/10.1103/PhysRevB.85.094503 ), tunneling ( https://journals.aps.org/prb/pdf/10.1103/PhysRevB.56.14677 ), Aharonov-Bohm (https://www.sciencedirect.com/science/article/pii/S0375960197003356  ) effects for these particle-like objects.

It brings question if this similarity with particle physics could be taken further? How far?
E.g. there is this famous Volovik's "The universe in helium droplet" book ( http://www.issp.ac.ru/ebooks/books/open/The_Universe_in_a_Helium_Droplet.pdf ).
Maybe let us discuss it here - any interesting approaches?

For example there are these biaxial nematic liquid crystals: of molecules with 3 distinguishable axes.
We could build hedgehog configuration (topological charge) with one these 3 axes, additionally requiring magnetic-like singularity for second axis due to hairy-ball theorem ... doesn't it resemble 3 leptons: asymptotically the same charge (+magnetic dipole), but with different realization/mass?

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Physics, Astronomy & Cosmology / Re: What is atomic orbial from QM interpretations perspective?

« on: 19/10/2020 14:18:29 »

Ps. Just found 2008 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.073003 "Scientists in Sweden film moving electron for the first time":

They see wave nature, but clearly localized - with traveling center, exactly as in walking droplets experiments https://dualwalkers.com/

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Physics, Astronomy & Cosmology / Re: What is atomic orbial from QM interpretations perspective?

« on: 19/10/2020 10:11:21 »

Remember that electron is charged - hence has accompanied electric field.

So what is electric field of orbital?
Is it superposition of electric field of electron being in each point?
Or maybe it is one electric field averaged over electron position?

I don't think that there is a qualitative change

Indeed we are entering the complementary principle ( https://en.wikipedia.org/wiki/Complementarity_(physics) ) allowing to measure only one at once.
But measurement is very destructive process, the question is if they are objectively both?
One experiment using both is Afshar's: https://en.wikipedia.org/wiki/Afshar_experiment
A more recent one "Simultaneous observation of the quantization and the interference pattern": https://www.nature.com/articles/ncomms7407
For atom-like models with orbital quantization, there are great walking droplets experiments e.g. https://www.nature.com/articles/ncomms4219 or www.pnas.org/content/107/41/17515.short