Qubits Explained: What a Qubit Is, the Main Types and Why They Are Fragile
What is a qubit?
A bit is 0 or 1. A qubit is a quantum system with two distinguishable states that can also be in a combination of both, called a superposition. Each state has an amplitude, and when you measure, you get 0 or 1 with probability set by the squared amplitude. Two qubits can also be entangled, meaning their results are correlated. A line of qubits is described by a number of amplitudes that doubles with every added qubit, which is why even modest quantum machines are hard to simulate on ordinary computers. For the basic idea, see what is a qubit and IBM's overview linked below. This page covers a different question: what qubits are physically made of and why they are hard to keep working.
What are qubits made of?
Any physical system with two controllable states could serve in principle. The main approaches today are below. Each company's choice is a bet about which trade offs will win.
| Type | The qubit is | How it is controlled | Strengths | Challenges |
|---|---|---|---|---|
| Superconducting | A tiny electrical circuit (for example a transmon) cooled near absolute zero | Microwave pulses | Fast operations, built with chip fabrication methods | Needs dilution refrigerators, fixed wiring between qubits, noise |
| Trapped ion | A single charged atom held in an electromagnetic trap | Lasers | Very uniform qubits, any pair can interact in a trap | Slower operations, harder to scale to many qubits |
| Neutral atom | An uncharged atom held by laser tweezers | Lasers | Large arrays that can be rearranged | Operations and atom loss still being improved |
| Photonic | A particle of light in an optical chip | Optical circuits | Light travels well and resists some noise | Photons do not easily interact, so gates are hard |
| Spin in silicon | The spin of an electron or nucleus in silicon | Microwaves and electric fields | Tiny and compatible with chip making | Control and uniformity at scale |
Read more on each in superconducting qubits, silicon spin qubits, topological qubits and types of quantum computers.
Why are qubits so fragile?
A qubit's quantum state is easily disturbed. Heat, stray electromagnetic fields, vibrations and imperfect control pulses all leak information from the qubit into its surroundings, a process called decoherence. When that happens the superposition collapses into an ordinary mix and the computation is corrupted. Qubits also pick up small errors from every gate. Two numbers describe quality: how long a qubit keeps its state (coherence time) and how often an operation goes wrong (error rate or fidelity). A machine with many qubits but high error rates cannot run long programs.
Why not just copy the qubit to protect it?
Quantum states cannot be copied exactly (the no-cloning theorem), so the classical trick of keeping three copies and voting does not work directly. Quantum error correction instead spreads one logical qubit across many physical qubits and measures parity checks that reveal errors without revealing the data. This needs many physical qubits per logical qubit and operations accurate enough that corrections add less error than they remove. In December 2024 Google reported that errors fell as its error correcting code grew on its 105 qubit Willow chip, described as below the threshold needed for scaling (Nature, linked below). IBM has published a target of 200 logical qubits by 2029, a plan rather than a delivered machine. See logical vs physical qubits.
What does this mean for headline qubit counts?
A larger number of physical qubits is not automatically better. A thousand noisy qubits may be less useful than a hundred accurate ones, and different technologies are not directly comparable. When you read a qubit count, ask whether it is physical or logical, how accurate the operations are, and whether the claim comes from a peer reviewed result or a roadmap. John Preskill's term for the current era is noisy intermediate scale quantum (NISQ). See how to read quantum news without hype.
Where does QNT fit?
It does not. QUANTUM (QNT) is a community token on Solana with a quantum theme. It contains no qubits and does not perform quantum computation. For the crypto link, see blockchain vs quantum computing.
Sources and further reading
- IBM: What is quantum computing?
- Preskill: Quantum Computing in the NISQ era and beyond (arXiv)
- Google: Meet Willow, our state-of-the-art quantum chip
- Nature: Quantum error correction below the surface code threshold
- IBM Quantum blog: large scale fault tolerant quantum computing (10 June 2025)
- Wikipedia: quantum decoherence
- Wikipedia: transmon
Checked 2026-10-12. Company claims are the companies' own and roadmaps are plans, so check the primary sources. This is education, not investment or security advice. QUANTUM (QNT) is an independent community token on Solana and is not affiliated with Quantinuum (Nasdaq: QNT) or Quant Network (QNT on Ethereum).
Frequently asked questions
What is a qubit made of?
It depends on the technology: a superconducting circuit, a trapped ion, a neutral atom, a photon or an electron spin. Each is a controllable two level quantum system.
Why are qubits fragile?
Noise from heat, fields and imperfect control destroys the qubit's quantum state, a process called decoherence.
Are more qubits always better?
No. Accuracy matters as much as count, and physical and logical qubits are different units.
Does QNT use qubits?
No. QUANTUM (QNT) is a community token on Solana and has no quantum hardware.
Next read
What Is a Qubit? Superposition and Measurement ExplainedA qubit is the basic unit of a quantum computer. Learn how qubits work, how they are built, and why they are fragile.Read nextAlso useful: Types of Quantum Computers: Superconducting, Ion, Photonic and More | Superconducting Qubits Explained in Depth | Logical vs Physical Qubits: How Quantum Resource Estimates Work
Educational content, not financial advice. QUANTUM (QNT) is independent of Quantinuum (Nasdaq: QNT) and Quant Network (QNT on Ethereum). Live chart | Token facts