QuTech Academy video lectures
QuTech, TU Delft
Free lecture videos from the Delft MOOCs, organised by topic. Uniquely strong on the hardware side — how you actually build and control a qubit — and on quantum internet.
Intermediate · 4 resources
Quantum key distribution (BB84)
A protocol for two parties to agree on a shared secret key such that any eavesdropper necessarily disturbs the transmission and is detected — security resting on physics rather than on computational hardness.
Why it matters
It is deployed commercially today and is the most mature quantum technology. It is also frequently confused with post-quantum cryptography, which is a completely different thing.
After this you will be able to
- Walk through BB84 step by step
- Explain how eavesdropping is detected
- Distinguish QKD from post-quantum cryptography
Start here
2 best places to start
Hand-picked and ordered. If you only have time for one, take the first.
Quantum Computing: Lecture Notes
Ronald de Wolf (CWI / QuSoft)
Free, self-contained and rigorous, with exercises. Widely used as the standard course text in Europe and the best single free replacement for a paid textbook.
Also covering this
2 more resources
No-cloning theorem
Wikipedia
You cannot copy an unknown quantum state. The one-line proof is genuinely accessible, and this single fact explains teleportation, QKD security and why error correction is hard.
Quantum computing courses on edX
edX (MIT, Delft, Berkeley and others)
The university MOOC hub. MIT's Quantum Information Science series and Delft's hardware-focused courses are the standouts. Audit tracks are free; certificates cost money.