How Does a Quantum Computer Work?

A quantum computer is not just a faster version of your laptop — it computes in a fundamentally different way. Instead of bits that are either 0 or 1, it uses qubits that exploit the strange rules of quantum mechanics to tackle certain problems that would defeat any classical machine.

Bits vs qubits

A normal computer stores information in bits: each is either 0 or 1. A quantum computer uses qubits, which can be 0, 1, or — thanks to superposition — a blend of both at once.

• With 2 classical bits you represent one of 4 values.
• With 2 qubits in superposition you can encode all 4 possibilities simultaneously.
• Add qubits and this grows exponentially: 300 qubits can represent more states than there are atoms in the observable universe.

The two quantum tricks

1. Superposition — a qubit holds many possibilities at once, so a quantum computer can explore a vast space of answers in parallel.
2. Entanglement — qubits become linked, so their states are correlated, letting the machine coordinate across all those possibilities.

Clever quantum algorithms arrange for the wrong answers to cancel out (through interference) and the right answers to reinforce, so a useful result emerges when you measure.

The hard part: qubits are fragile

Qubits lose their quantum behaviour almost instantly if disturbed — a problem called decoherence. To fight it, quantum computers are:

• cooled to near absolute zero (colder than deep space),
• shielded from vibration and stray fields, and
• protected by quantum error correction, which spreads one logical qubit across many physical ones.

Different companies build qubits differently — superconducting circuits (IBM, Google), trapped ions (IonQ, Quantinuum), and photons (PsiQuantum, Quandela).

What are they good for?

Not everyday tasks. Quantum computers target specific problems: simulating molecules for drug and materials discovery, optimization, and cryptography. See our overview of the quantum computing companies racing to build them.

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