Genius: Richard Feynman and Modern Physics by James Gleick (1994) by 
Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01It has some overlap with Surely You're Joking, Mr. Feynman, which it likely takes as primary sources of some stories.
However, while Surely goes into a lot of detail of each event, this book paints a more cohesive and global picture of things.
In terms of hard physics/mathematics, this book takes the approach of spending a few paragraphs in some chapters describing in high level terms some of the key ideas, which is a good compromise. It does sometime fall into the sin of to talk about something without giving the real name to not scare off the audience, but it does give a lot of names, notably it talks a lot about Lagrangian mechanics. And it goes into more details than Surely in any case.
Without me, my stack is useless. Without my stack, I am useless. I must fire my requests true. I must shoot straighter than my hackers who are trying to kill me. I must shoot him before he shoots me. I will ...My stack is human, even as I am human, because it is my life. Thus, I will learn it as a brother. I will learn its weaknesses, its strength, its parts, its accessories, its ORMs and its asset bundlers. I will keep my stack clean and ready, even as I am clean and ready. We will become part of each other. We will ...
Explanation: this is an allusion to the Rifleman's Creed. This particular version talks about the website stack chosen for a website, i.e. the libraries used.
Ciro Santilli has always felt that choosing a stack is an almost religious choice. It is perhaps part of why the prayer style of the original Rifleman's Creed resonates with the web stack choice.
It is very hard to know how things are going go, the ups and downs, before putting big hours into it.
And once you start, it is hard, though not impossible, to move away.
Wave equation solution with Fourier series by Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01eigenvalue problem of Laplace's equation.
Set of all decision problems solvable by a Turing machine, i.e. that decide if a string belongs to a recursive language.
One of the four following states:
The Bell states are entangled and non-separable. Intuitively, we can see that when we measure that state, the values of the first and second bit are strictly correlated. This is the hallmark of quantum computation: making up states where qubits are highly correlated to match a specific algorithmic answer, and opposed to uniformly random noise. For example, the Bell state circuit is a common hello world, e.g. it is used in the official Qiskit hello world.
Quantum logic gates are needed for physical implementation by Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01
Ciro Santilli 37 Updated 2025-06-17 +Created 1970-01-01One direct practical reason is that we need to map the matrix to real quantum hardware somehow, and all quantum hardware designs so far and likely in the future are gate-based: you manipulate a small number of qubits at a time (2) and add more and more of such operations.
While there are "quantum compilers" to increase the portability of quantum programs, it is to be expected that programs manually crafted for a specific hardware will be more efficient just like in classic computers.
TODO: is there any clear reason why computers can't beat humans in approximating any unitary matrix with a gate set?
This is analogous to what classic circuit programmers will do, by using smaller logic gates to create complex circuits, rather than directly creating one huge truth table.
The gates themselves are just unitary matrices that operate on the input qubits and produce the same number of output qubits.
For example, the matrix for the CNOT gate, which takes 2 qubits as input is:
1 0 0 0
0 1 0 0
0 0 0 1
0 0 1 0The final question is then: if I have a 2 qubit gate but an input with more qubits, say 3 qubits, then what does the 2 qubit gate (4x4 matrix) do for the final big 3 qubit matrix (8x8)? In order words, how do we scale quantum gates up to match the total number of qubits?
The intuitive answer is simple: we "just" extend the small matrix with a larger identity matrix so that the sum of the probabilities third bit is unaffected.
More precisely, we likely have to extend the matrix in a way such that the partial measurement of the original small gate qubits leaves all other qubits unaffected.
For example, if the circuit were made up of a CNOT gate operating on the first and second qubits as in:
0 ----+----- 0
|
1 ---CNOT--- 1
2 ---------- 2TODO lazy to properly learn right now. Apparently you have to use the Kronecker product by the identity matrix. Also, zX-calculus appears to provide a powerful alternative method in some/all cases.
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