Quantum computers make headlines with claims of solving in minutes what supercomputers would take thousands of years to do. They are real and improving fast, but they are not faster versions of your laptop. They are a different kind of machine, built for particular problems.
Bits versus qubits
An ordinary computer stores information as bits, each either 0 or 1. A quantum computer uses qubits. A qubit can be in a blend of 0 and 1 at the same time, called superposition, until it is measured. When measured, it gives 0 or 1 with certain probabilities.
Qubits can also be entangled, meaning their states are linked so that measuring one tells you something about the other, however far apart they are. Combining superposition and entanglement lets a quantum computer represent a huge number of possibilities at once.
How a quantum calculation works
A quantum algorithm uses operations called gates to steer the qubits so that wrong answers cancel each other out and right answers reinforce, much like the wave cancellation inside noise-cancelling headphones. When the qubits are finally measured, the right answer is the most likely result. The art is designing algorithms where this interference works in your favour.
What quantum computers could be good at
- Chemistry and materials: simulating molecules for new medicines, catalysts and battery materials.
- Optimisation: certain logistics, scheduling and finance problems.
- Cryptography: a large enough quantum computer could break widely used encryption schemes. That is why new post-quantum encryption standards were published by the US standards body NIST in 2024 and are being adopted worldwide.
For everyday tasks like browsing, gaming or spreadsheets, ordinary computers will remain better.
The engineering challenge: keeping qubits quiet
Qubits are fragile. Heat, vibration and stray electromagnetic signals destroy their quantum state in a fraction of a second, a problem called decoherence. Many quantum computers cool their chips to a few thousandths of a degree above absolute zero inside large refrigerators. Others use trapped ions, neutral atoms or particles of light.
Because errors are constant, the field's big goal is error correction: combining many physical qubits into one reliable logical qubit. Recent experiments have shown error correction improving as systems grow, a key milestone towards useful machines.
Where things stand
Today's machines have from dozens to over a thousand physical qubits but still make too many errors for most practical problems. Experts expect the first commercially valuable uses in chemistry and materials science, with timelines debated from a few years to more than a decade. India's National Quantum Mission is funding research in quantum computing, communication and sensing.
Frequently asked questions
Will quantum computers replace normal computers?
No. They will work alongside classical computers, handling specialised problems, much as GPUs handle graphics and AI today.
Is my bank account at risk?
Not today. Banks and tech companies are already moving to post-quantum encryption well before a large enough quantum computer exists.