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Symbols, letters, and the classical logic underneath
Quantum computing borrows heavily from two older toolkits: the logic gates every digital computer is built from, and the Greek letters mathematicians use as names. This page collects both, plus the notation used throughout the series, in one place.
01 · Classical logic gates
The seven gates every digital computer uses
A logic gate takes one or two input bits and produces one output bit. Combine enough of them and you get adders, memory, and processors. Flip the inputs below and every gate updates at once.
Try it: set the inputs
Writing logic in math and in code
| Operation | Math symbols | Python / C bit operator | Where it shows up |
|---|---|---|---|
| AND | A ∧ B, A·B | a & b | Toffoli target, masks |
| OR | A ∨ B, A + B | a | b | Setting flags |
| XOR | A ⊕ B | a ^ b | CNOT (Quantum 04), one-time pads, BB84 key bits |
| NOT | ¬A, Ā | 1 - a or a ^ 1 | Pauli-X (Quantum 04) |
In Python, ~a flips every bit of an integer and gives -a - 1, so for a single 0/1 bit use a ^ 1 instead.
02 · Greek alphabet
The 24 Greek letters, and where you'll meet them
Mathematicians run out of Latin letters fast, so Greek letters name angles, amplitudes, states, and sums. The letters this series actually uses are marked, so you know which ones to learn first.
| Upper | Lower | Name | English | Where you'll see it |
|---|
Variant shapes you may see in other textbooks: ϕ for φ, ϑ for θ, ϵ for ε. Lowercase sigma becomes ς at the end of a Greek word.
03 · Notation cheat sheet
How to read the symbols in this series
Read-aloud names help when you're discussing a problem with someone.
| Symbol | Read as | Meaning | First seen |
|---|