C3 Updated 2025-07-16
Physics course of the University of Oxford structure Updated 2025-07-16
Physics bibliography Updated 2025-07-16
Photon polarization Updated 2025-07-16
The knowledge that light is polarized precedes the knowledge of the existence of the photon, see polarization of light for the classical point of view.
The polarization state and how it can be decomposed into different modes can be well visualized with the Poincaré sphere.
One key idea about photon polarization is that it carries angular momentum. Therefore, when an electron changes orbitals in the Schrödinger equation solution for the hydrogen atom, the angular momentum (as well as energy) change is carried out by the polarization of the photon!
- clear animations showing how two circular polarizations can make a vertical polarization
- a polarizer can be modelled bra operator.
- light polarization experiments are extremely direct evidence of quantum superposition. Individual photons must be on both L and R states at the same time because a V filter passes half of either L or R single photons, but it passes all L + R photons
Photonic quantum computer Updated 2025-07-16
The key experiment/phenomena that sets the basis for photonic quantum computing is the two photon interference experiment.
The physical representation of the information encoding is very easy to understand:
- input: we choose to put or not photons into certain wires or no
- interaction: two wires pass very nearby at some point, and photons travelling on either of them can jump to the other one and interact with the other photons
- output: the probabilities that photos photons will go out through one wire or another
Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)
Source. This is a good introduction to a photonic quantum computer. Highly recommended.- youtube.com/watch?v=7wCBkAQYBZA&t=1285 shows an experimental curve for a two photon interference experiment by Hong, Ou, Mandel (1987)
- youtube.com/watch?v=7wCBkAQYBZA&t=1440 shows a KLM CNOT gate
- youtube.com/watch?v=7wCBkAQYBZA&t=2831 discusses the quantum error correction scheme for photonic QC based on the idea of the "Raussendorf unit cell"
Photon Updated 2025-07-16
Initially light was though of as a wave because it experienced interference as shown by experiments such as:
But then, some key experiments also start suggesting that light is made up of discrete packets:and in the understanding of the 2020 Standard Model the photon is one of the elementary particles.
- Compton scattering, also suggests that photons carry momentum
- photoelectric effect
- single photon production and detection experiments
This duality is fully described mathematically by quantum electrodynamics, where the photon is modelled as a quantized excitation of the photon field.
Photomask Updated 2025-07-16
Photoelectric effect Updated 2025-07-16
No matter how hight the wave intensity, if it the frequency is small, no photons are removed from the material.
This is different from classic waves where energy is proportional to intensity, and coherent with the existence of photons and the Planck-Einstein relation.
Phi Updated 2025-07-16
Phase shift gate Updated 2025-07-16
Phaser.js Updated 2025-07-16
Likely the best JavaScript 2D game engine as of 2023.Uses Matter.js as a physics engine if enabled. There's also an alternative (in-house?) "arcade" engine: photonstorm.github.io/phaser3-docs/Phaser.Physics.Arcade.ArcadePhysics.html but it appears to be simpler/less robust (but also possibly faster).
- github.com/photonstorm/phaser
- phaser.io/
- phaser.io/examples/v3.85.0/games contains the demo games
Phagocytosis Updated 2025-07-16
Peter Todd's hash collision puzzles Updated 2025-07-16
As mentioned at the prize was claimed at 8d31992805518fd62daa3bdd2a5c4fd2cd3054c9b3dca1d78055e9528cff6adc (2017-02-23) which spends several inputs with the same unlock script that presents two different constantants that have the same SHA-1:both givingIt was claimed on the same day that Google disclosed the collision: security.googleblog.com/2017/02/announcing-first-sha1-collision.html
printf 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 | xxd -r -p | sha1sum
printf 255044462d312e330a25e2e3cfd30a0a0a312030206f626a0a3c3c2f57696474682032203020522f4865696768742033203020522f547970652034203020522f537562747970652035203020522f46696c7465722036203020522f436f6c6f7253706163652037203020522f4c656e6774682038203020522f42697473506572436f6d706f6e656e7420383e3e0a73747265616d0affd8fffe00245348412d3120697320646561642121212121852fec092339759c39b1a1c63c4c97e1fffe017346dc9166b67e118f029ab621b2560ff9ca67cca8c7f85ba84c79030c2b3de218f86db3a90901d5df45c14f26fedfb3dc38e96ac22fe7bd728f0e45bce046d23c570feb141398bb552ef5a0a82be331fea48037b8b5d71f0e332edf93ac3500eb4ddc0decc1a864790c782c76215660dd309791d06bd0af3f98cda4bc4629b1 | xxd -r -p | sha1sumf92d74e3874587aaf443d1db961d4e26dde13e9cBoth of these are PDF prefixes, so they start with the PDF file signature, but are not fully viewable PDFs on their own.
Polytechnic Institute of Paris Updated 2025-07-16
Penalty kick left right Nash equilibrium Updated 2025-07-16
And before he kicks, the goalkeeper must also decide left or right, because there is no time to see where the ball is going.
Because the kicker is right footed however, he kicker kicks better to one side than the other. So we have four probabilities:
- goal kick left keeper jumps left
- goal kick right keeper jumps right
- goal kick left keeper jumps right. Note that it is possible that this won't be a goal, even though the keeper is nowhere near the ball, as the ball might just miss the goal by a bit.
- kick right and keeper jumps left. Analogous to above
PC game Updated 2025-07-16
Paulo Freire Updated 2025-07-16
en.wikipedia.org/wiki/Paulo_Freire:OMG so nice.
During his childhood and adolescence, Freire ended up four grades behind, and his social life revolved around playing pick-up football with other poor children, from whom he claims to have learned a great deal. These experiences would shape his concerns for the poor and would help to construct his particular educational viewpoint. Freire stated that poverty and hunger severely affected his ability to learn. These experiences influenced his decision to dedicate his life to improving the lives of the poor: "I didn't understand anything because of my hunger. I wasn't dumb. It wasn't lack of interest. My social condition didn't allow me to have an education. Experience showed me once again the relationship between social class and knowledge"
Pauli-X gate Updated 2025-07-16
The quantum NOT gate swaps the state of and , i.e. it maps:As a result, this gate also inverts the probability of measuring 0 or 1, e.g.
- if the old probability of 0 was 0, then it becomes 1
- if the old probability of 0 was 0.2, then it becomes 0.8
Paul Allen Updated 2025-07-16
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