Skip to content
QuantumO

Classical vs. Quantum Computing

BeginnerQuantum computing7 min read

By QuantumO Editorial · Scientific reviewer: not yet assigned · Published · Updated

In short

Classical computers process definite bits through logic gates; quantum computers process qubits through reversible gates that manipulate amplitudes. Quantum machines are expected to help with specific problems such as simulating quantum systems and certain factoring or search tasks, not with general everyday computing.

Watch the lesson

Video coming soon

This entry is a CMS placeholder. Add the YouTube video ID, thumbnail, duration and publication date to activate the player.

Visit the channel
Video details and transcript

Different machines for different problems

Classical hardware is astonishingly good at arithmetic, databases, graphics, and nearly everything else you do daily. Quantum hardware is slower, noisier, and far more expensive per operation.

The interest is not raw speed. It is that for a small set of problems the number of steps required scales much better on a quantum machine.

Where a quantum advantage is expected

Simulating molecules and materials is the clearest case, because the problem is itself quantum. Certain number-theoretic problems, including integer factoring, have known quantum algorithms with large asymptotic speedups. Some search and optimisation tasks have modest quadratic improvements.

For most workloads — spreadsheets, video, web serving, ordinary machine learning — no advantage is expected.

Analogy: a wind tunnel, not a faster car

A quantum computer is closer to specialised laboratory equipment than to a faster laptop: enormously valuable for particular questions, irrelevant for most. As with all analogies here, it describes the role, not the mechanism.

Common misconceptions

Claim: Quantum computers will replace ordinary computers.
More accurately: They are expected to work alongside classical systems, handling narrow subroutines while classical machines do everything else.

Important terminology

Classical bit
A classical bit is a unit of information that is either 0 or 1 at any moment.
Qubit
A qubit is the basic unit of quantum information: a two-level quantum system that can hold a combination of the outcomes 0 and 1.
Quantum circuit
A quantum circuit is a sequence of quantum gates applied to qubits, usually ending in measurement.
Interference
Interference is the adding and cancelling of quantum amplitudes that steers a system toward some outcomes and away from others.

Frequently asked questions

Can quantum computers replace ordinary computers?
No. Quantum processors are specialised and are expected to be used as accelerators for particular problems, with classical computers handling the rest.
Video transcript

Transcript not available yet. Transcripts are stored as an editable CMS field on each video record.

Sources and further reading

Keep going