Bryan McAllister’s personal reference notebook
September 12, 2026Short & citedBlog
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Field Notes • Quantum Computing

Quantum computer

A quantum computer is a computing device that uses quantum-mechanical effects, such as superposition, entanglement, and interference, to process information.

Updated September 12, 20261 min readCited sources

A quantum computer is a computing device that uses quantum-mechanical effects—superposition, entanglement, and interference—to process information. It relies on qubits instead of classical bits and is expected to excel at specialized problems like simulations and certain cryptographic tasks.

What it is

Quantum computers encode information in qubits, which can exist in superposition (multiple states at once) and become entangled. This changes how information is processed, allowing some computations to be performed much faster than on classical computers.

Why it matters

Quantum computers could dramatically speed up problems involving simulation, optimisation, and algorithms that exploit quantum interference. Potential applications include modelling chemical and physical systems, cryptanalysis, and scientific modelling.

Current limitations

Most present-day quantum computers are still experimental, noisy, and suited only to specialised tasks. Building scalable, reliable, universal machines remains an active research challenge, and they are not yet widely used outside research.

In short

  • Quantum computers use qubits and quantum effects like superposition and entanglement.
  • They can potentially outperform classical computers on certain specialised tasks.
  • Current hardware is experimental and error-prone, with limited real-world use.
  • Canadian researchers and companies are active in quantum computing development.
Canadian angle

Canadian researchers, universities, and companies are active in quantum computing research and development, and Canada has a visible role in the global quantum technology ecosystem. This topic is also relevant to Canadian readers because of its implications for cybersecurity, science, and advanced computing.

Quick questions

What is a quantum computer?
A quantum computer is a computer that uses quantum-mechanical states to store and process information instead of ordinary binary bits.
What is a qubit?
A qubit, or quantum bit, is the basic unit of information in quantum computing and can exist in a superposition of states.
Are quantum computers widely used today?
No. Current quantum computers are still experimental and error-prone, so they are mainly used in research and specialised demonstrations.

Sources

  1. Wikipedia — https://en.wikipedia.org/wiki/Quantum_computing
    Supports: Definition of quantum computer, use of quantum states, qubits, superposition, entanglement, and potential applications.
  2. Encyclopaedia Britannica — https://www.britannica.com/technology/quantum-computer
    Supports: General definition of a quantum computer as a device using quantum mechanics.
  3. NIST — https://www.nist.gov/quantum-information-science/quantum-computing-explained
    Supports: Qubits, superposition, entanglement, current limitations, and potential for faster problem solving.
  4. IBM — https://www.ibm.com/think/topics/quantum-computing
    Supports: Core distinctions from classical computers, qubits, and quantum phenomena used in computation.
  5. Microsoft — https://learn.microsoft.com/en-us/azure/quantum/overview-understanding-quantum-computing
    Supports: Features of a good quantum computer and the role of quantum phenomena in computation.
  6. Google Quantum AI — https://quantumai.google/whatisqc
    Supports: Exponential computational space from qubits and superposition; general explanation of quantum computing.