A computer that stores and manipulates information using quantum physics, letting it explore many computational paths at once and interfere them so the wrong answers cancel out.
Why it matters
Every other topic hangs off this one. Getting the framing right early stops you absorbing the two most common myths: that a quantum computer "tries all answers in parallel", and that it will replace your laptop.
After this you will be able to
A quantum computer is a co-processor for a narrow class of problems. It has a slow clock speed, tiny memory and a high error rate. It wins only where the interference trick applies, and loses badly everywhere else.
A GPU is not a fast CPU — it is a different shape of machine that is spectacular at one class of work and poor at the rest. Quantum processors are a further step in that direction.
One day quantum computers will replace classical ones.
They will sit alongside them, most likely as a cloud service you call for particular subroutines — the way you currently reach for a GPU cluster.
Every realistic architecture is hybrid: classical computers running the program, calling out to quantum hardware for the specific subroutine that benefits.
Hand-picked and ordered. If you only have time for one, take the first.
The single best starting point in existence. An essay built on spaced-repetition flashcards embedded in the text, so you actually remember it a month later. Assumes nothing but curiosity, and gets you honestly to quantum teleportation.
IBM's free structured course platform and the successor to the old Qiskit Textbook. Mixes written lessons, videos and runnable notebooks, and takes you from 'what is a qubit' to running jobs on real hardware.
Free lecture notes connecting quantum computing to complexity theory, cryptography, free will and the anthropic principle. Funny, opinionated, and the best correction to hype you will find.
Microsoft's concept documentation is unusually well written for docs — the pages on qubits, entanglement and the Q# language work as standalone explanations.
A free, complete undergraduate textbook with worked exercises. Uniquely, it teaches classical computing alongside quantum, so the comparison is always concrete rather than hand-waved.
Science journalism that researchers actually respect. The best way to follow real results without either the arXiv firehose or press-release hyperbole.
Interactive, visual and gentle, built in collaboration with quantum researchers. Worth it if you learn best by poking at widgets; everything it covers is available free elsewhere with more effort.
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.
Topics that list What is quantum computing? as a prerequisite.
The quantum version of a bit. Instead of being 0 or 1, a qubit carries two numbers (amplitudes) that say how much of "0" and how much of "1" it holds — including negative and complex values.
BeginnerQuantum computers give large speedups on a narrow, structured set of problems. They are not faster at general computing, they do not "solve NP-complete problems instantly", and they will not run your spreadsheet.
Beginner