Curriculum / Quantum Hardware & NISQ / How Quantum Computers Are Built
How Quantum Computers Are Built
Survey the major physical platforms for quantum computing.
How Quantum Computers Are Built
Quantum computers are not just faster classical computers. They exploit fundamentally different physics, superposition, entanglement, interference, and that physics has to be embodied in real matter. Today a handful of competing hardware technologies are racing to build the first fault-tolerant quantum computer. Each approach has distinct strengths, weaknesses, and scaling challenges.
The Physical Qubit Problem
A classical bit can be any physical system with two stable states: a transistor (on/off), a magnetic domain (up/down), a capacitor (charged/uncharged). These systems are robust because classical states are macroscopic and noise-resistant.
A qubit must maintain quantum coherence, superposition and entanglement, while being:
- 1.Isolatable: Protected from environmental noise that collapses quantum states
- 2.Controllable: Able to be precisely manipulated with gates
- 3.Measurable: Readable at the end of computation
- 4.Initializable: Resettable to a known fiducial state (e.g. ) before computation begins
- 5.Scalable: Replicable to thousands or millions
These requirements are in tension. Better isolation reduces control. Better measurement destroys coherence. This is the DiVincenzo criteria for a useful quantum computer.
Qubit Technologies Overview
| Technology | Company | Qubit Count (2024) | Coherence | Gate Speed |
|---|---|---|---|---|
| Superconducting | IBM, Google, Rigetti | 100 - 1000 | 10 - 500 us | 10 - 100 ns |
| Trapped Ion | IonQ, Quantinuum | 20 - 64 | 1 - 100 s | 1 - 100 us |
| Photonic | PsiQuantum, Xanadu | ~100 (demonstrations) | Room temp | Speed of light |
| Neutral Atom | QuEra, Pasqal | 1000 - 10000 | 1 - 10 s | 0.1 - 1 us |
| Spin Qubit | Intel, Delft | 6 - 12 | 1 - 100 ms | 1 - 100 ns |
| Topological | Microsoft | Prototype stage | Long (theory) | Fast (theory) |
This is the opening of the lesson. The full walkthrough, the interactive circuit, and the graded challenge continue inside myqubit.
How this lesson works
A guided reading lesson with interactive knowledge checks. Concepts are explained step by step with circuit diagrams and runnable examples, and you confirm understanding before moving on.
Part of: Quantum Hardware & NISQ
Explore the physics of real quantum computers, understand noise, and learn near-term algorithms designed for today's noisy hardware.
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