Position and momentum space Updated 2025-07-16
One of the main reasons why physicists are obsessed by this topic is that position and momentum are mapped to the phase space coordinates of Hamiltonian mechanics, which appear in the matrix mechanics formulation of quantum mechanics, which offers insight into the theory, particularly when generalizing to relativistic quantum mechanics.
One way to think is: what is the definition of space space? It is a way to write the wave function such that:And then, what is the definition of momentum space? It is of course a way to write the wave function such that:
- the position operator is the multiplication by
- the momentum operator is the derivative by
- the momentum operator is the multiplication by
physics.stackexchange.com/questions/39442/intuitive-explanation-of-why-momentum-is-the-fourier-transform-variable-of-posit/39508#39508 gives the best idea intuitive idea: the Fourier transform writes a function as a (continuous) sum of plane waves, and each plane wave has a fixed momentum.
Bibliography:
PostgreSQL Updated 2025-07-16
PostgreSQL feels good.
Its feature set is insanely large! Just look at stuff like: stackoverflow.com/questions/1986491/sql-split-string-by-space-into-table-in-postgresql/1993058#1993058
If Oracle is the Microsoft of database, Postgres is the Linux, and MySQL (or more precisely MariaDB) is the FreeBSD (i.e. the one that got delayed by legal issues). Except that their software licenses were accidentally swapped.
The only problem with Postgres is its name. PostgreSQL is so unpronounceable and so untypeable that you should just call it "Postgres" like everyone else.
German learned society Updated 2025-07-16
Helium Updated 2025-07-16
PostgreSQL logging Updated 2025-07-16
Ubuntu 21.10 has a certain default level of logging by default to:but it does not log everything, only/mostly errors it seems.
/var/log/postgresql/postgresql-13-main.logSetting:under:and then restarting the server:just works.
log_statement = 'all'/etc/postgresql/13/main/postgresql.confsudo service restart postgresqlRealtime monitoring for long queries instead: stackoverflow.com/questions/8597516/app-to-monitor-postgresql-queries-in-real-time
Power, performance and area Updated 2025-07-16
This is the mantra of the semiconductor industry:
- power and area are the main limiting factors of chips, i.e., your budget:
- chip area is ultra expensive because there are sporadic errors in the fabrication process, and each error in any part of the chip can potentially break the entire chip. Although there areThe percentage of working chips is called the yield.In some cases however, e.g. if the error only affects single CPU of a multi-core CPU, then they actually deactivate the broken CPU after testing, and sell the worse CPU cheaper with a clear branding of that: this is called binning www.tomshardware.com/uk/reviews/glossary-binning-definition,5892.html
- power is a major semiconductor limit as of 2010's and onwards. If everything turns on at once, the chip would burn. Designs have to account for that.
- performance is the goal.Conceptually, this is basically a set of algorithms that you want your hardware to solve, each one with a respective weight of importance.Serial performance is fundamentally limited by the longest path that electrons have to travel in a given clock cycle.The way to work around it is to create pipelines, splitting up single operations into multiple smaller operations, and storing intermediate results in memories.
Representation of the Lorentz group Updated 2025-07-16
One of the representations of the Lorentz group that show up in the Representation theory of the Lorentz group.
State of the art Updated 2025-07-16
The Final Encyclopedia Updated 2025-07-16
Program Raspberry Pi Pico W with C Updated 2025-07-26
Ubuntu 22.04 build just worked, nice! Much feels much cleaner than the Micro Bit C setup:
sudo apt install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi libstdc++-arm-none-eabi-newlib
git clone https://github.com/raspberrypi/pico-sdk
cd pico-sdk
git checkout 2e6142b15b8a75c1227dd3edbe839193b2bf9041
cd ..
git clone https://github.com/raspberrypi/pico-examples
cd pico-examples
git checkout a7ad17156bf60842ee55c8f86cd39e9cd7427c1d
cd ..
export PICO_SDK_PATH="$(pwd)/pico-sdk"
cd pico-exampes
mkdir build
cd build
# Board selection.
# https://www.raspberrypi.com/documentation/microcontrollers/c_sdk.html also says you can give wifi ID and password here for W.
cmake -DPICO_BOARD=pico_w ..
make -jThen we install the programs just like any other UF2 but plugging it in with BOOTSEL pressed and copying the UF2 over, e.g.:Note that there is a separate example for the W and non W LED, for non-W it is:
cp pico_w/blink/picow_blink.uf2 /media/$USER/RPI-RP2/cp blink/blink.uf2 /media/$USER/RPI-RP2/Also tested the UART over USB example:You can then see the UART messages with:
cp hello_world/usb/hello_usb.uf2 /media/$USER/RPI-RP2/screen /dev/ttyACM0 115200TODO understand the proper debug setup, and a flash setup that doesn't require us to plug out and replug the thing every two seconds. www.electronicshub.org/programming-raspberry-pi-pico-with-swd/ appears to describe it, with SWD to do both debug and flash. To do it, you seem need another board with GPIO, e.g. a Raspberry Pi, the laptop alone is not enough.
Aluminium Updated 2025-07-16
Oxygen Updated 2025-07-16
ProtonMail Updated 2025-07-16
One of the very few encrypted emails... beauty. And they also have an encrypted password manager!!! Using this is a must as of 2023 basically. The only missing thing now is to find a fully open source alternative!!!
Sure, search capabilities have to be somewhat limited: proton.me/blog/engineering-message-content-search
techcrunch.com/2021/09/06/protonmail-logged-ip-address-of-french-activist-after-order-by-swiss-authorities/ you've fucking got to use Tor Browser with it if you want your IP to remain hidden, learn that...
Their backend is closed source: www.reddit.com/r/ProtonMail/comments/iyjqxf/is_protonmails_backend_open_source/
Are daily notifications without a recovery email possible? www.reddit.com/r/ProtonMail/comments/yjau8f/allow_daily_email_notifications_without_having_a/ OK, they do work actually.
The lack of Gmail dot trick is tragic however, and you have to pay for multiple aliases. But you can however create separate inboxes with the same cell phone verification however.
PsiQuantum Updated 2025-07-16
CEO: Jeremy O'Brien
Raised 215M in 2020: www.bloomberg.com/news/articles/2020-04-06/quantum-computing-startup-raises-215-million-for-faster-device
Good talk by CEO before starting the company which gives insight on what they are very likely doing: Video "Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)"
PsiQuantum appears to be particularly secretive, even more than other startups in the field.
They want to reuse classical semiconductor fabrication technologies, notably they have close ties to GlobalFoundries.
Nuclear fission Updated 2025-07-16
Public relations Updated 2025-07-16
The reason public relations is evil in modern society is because, like discrimination, public relations works by dumb association and not logic or fairness.
If you're the son of the killer, you're fucked.
This is unlike our ideal for law which attempts, though sometimes fails, at isolating cause and effect.
Python (programming language) Updated 2025-07-16
Examples under python.
Ciro Santilli's wife was studying a bit of basic Python for some job interviews, when she noticed:Damn right, girl, damn right.
Wow,inis so powerful! You can dofor x in list,for x in dictandif x in dictall with that single word!
Ciro remembers hearing about Python online briefly. It seemed like a distant thing from the Java/C dominated (and outdated) university courses. Then some teaching assistant mentioned during some course when Ciro was at École Polytechnique that Python was a great integration tool. That sounded cool.
Then finally, when the École Polytechnique mathematics department didn't let Ciro Santilli do his internship of choice due to grades and Ciro was at an useless last moment backup internship, he learned more Python instead of doing his internship job, and was hooked.
Polonium Updated 2025-07-16
Discovered by Marie Curie, published July 1999.
Pseudoscience Updated 2025-07-16
qiskit/initialize.py Updated 2025-07-16
In this example we will initialize a quantum circuit with a single CNOT gate and see the output values.
By default, Qiskit initializes every qubit to 0 as shown in the qiskit/hello.py. But we can also initialize to arbitrary values as would be done when computing the output for various different inputs.
Output:which we should all be able to understand intuitively given our understanding of the CNOT gate and quantum state vectors.
┌──────────────────────┐
q_0: ┤0 ├──■──
│ Initialize(1,0,0,0) │┌─┴─┐
q_1: ┤1 ├┤ X ├
└──────────────────────┘└───┘
c: 2/═════════════════════════════
init: [1, 0, 0, 0]
probs: [1. 0. 0. 0.]
init: [0, 1, 0, 0]
probs: [0. 0. 0. 1.]
init: [0, 0, 1, 0]
probs: [0. 0. 1. 0.]
init: [0, 0, 0, 1]
probs: [0. 1. 0. 0.]
┌──────────────────────────────────┐
q_0: ┤0 ├──■──
│ Initialize(0.70711,0,0,0.70711) │┌─┴─┐
q_1: ┤1 ├┤ X ├
└──────────────────────────────────┘└───┘
c: 2/═════════════════════════════════════════
init: [0.7071067811865475, 0, 0, 0.7071067811865475]
probs: [0.5 0.5 0. 0. ]quantumcomputing.stackexchange.com/questions/13202/qiskit-initializing-n-qubits-with-binary-values-0s-and-1s describes how to initialize circuits qubits only with binary 0 or 1 to avoid dealing with the exponential number of elements of the quantum state vector.
There are unlisted articles, also show them or only show them.