01Overview
In 1981 Feynman proposed simulating quantum systems with quantum systems; in 1985 Deutsch gave the quantum Turing machine. In 1994 Shor’s algorithm showed that a quantum computer could factor large integers efficiently; in 1996 Grover’s algorithm gave a quadratic speed-up for search. Quantum computing now had its killer application.
Qubits are fragile, and decoherence plus gate error are the engineering core of the field. Superconducting, trapped-ion, photonic and topological qubits are all being explored. In 2019 Google’s Sycamore claimed “quantum supremacy”; error-correcting codes and logical qubits are now the competitive front. Quantum computers will not replace classical ones, but they will change cryptography, materials simulation and optimisation.
02History
- 1981
Feynman's idea of quantum simulation
The starting thought of quantum computing.
- 1985
The quantum Turing machine
Deutsch's model.
- 1994
Shor's algorithm
Quantum factoring and discrete logarithms.
- 1996
Grover's algorithm
A quadratic speed-up for search.
- 2019
Quantum supremacy
The Sycamore sampling experiment.
03Core concepts
Qubit
A bit that can sit in a superposition of 0 and 1.
Superposition and entanglement
The two resources behind quantum parallelism and strong correlation.
Quantum error correction
Encode one logical qubit in many physical ones to resist noise.
04Hands-on
Do it once — it beats reading it ten times
Run a Bell-state circuit on a simulator, then explain why measuring one qubit fixes the other
05Self-check
Say it in your own words first, then open the answer. Whatever you cannot explain is what to review next.
Can you explain "Qubit"?
A bit that can sit in a superposition of 0 and 1.
Can you explain "Superposition and entanglement"?
The two resources behind quantum parallelism and strong correlation.
Can you explain "Quantum error correction"?
Encode one logical qubit in many physical ones to resist noise.
What problem did it solve, and why was there nothing better at the time?
Go back to the history section: how was this done before, and what did it cost?
If you had to build it today, how would you break it down?
Use the hands-on task above: write a plan of at most three steps before you start.
06Key people
Richard Feynman
1918 – 1988
Proposed quantum simulation.
Peter Shor
1963 –
The quantum factoring algorithm.
07Further reading
- Quantum Computation and Quantum Information
- Quantum Supremacy Using a Programmable Superconducting Processor