You have probably heard that quantum computers will revolutionise everything from drug discovery to cryptography. But what actually is a quantum computer, and how is it different from the laptop or phone you are reading this on?
The answer requires understanding a bit of quantum physics — but do not worry, we will keep it simple.
Classical Computers vs Quantum Computers
Every classical computer — from your smartphone to the world’s most powerful supercomputers — processes information using bits. A bit is the smallest unit of data and can only be in one of two states: 0 or 1. Everything your computer does — every calculation, every image, every word — is ultimately a series of 0s and 1s.
A quantum computer uses qubits (quantum bits) instead. And here is where it gets interesting.
What Is Superposition?
In quantum mechanics, particles can exist in multiple states simultaneously until they are observed or measured. This property is called superposition.
A qubit, unlike a classical bit, can be 0, 1, or both 0 and 1 at the same time — until it is measured, at which point it collapses to one definite value.
Think of it this way: a classical bit is like a coin lying flat — it is either heads or tails. A qubit is like a coin spinning in the air — it is effectively both heads and tails simultaneously, until it lands.
With just 3 classical bits, you can represent one of 8 possible values (000, 001, 010… 111) at any given time. With 3 qubits in superposition, you can represent all 8 values simultaneously. Scale that up to 300 qubits, and you can represent more states simultaneously than there are atoms in the observable universe.
What Is Entanglement?
The second key quantum phenomenon is entanglement. When two qubits become entangled, the state of one is instantly correlated with the state of the other — no matter how far apart they are.
Measure one entangled qubit and you instantly know something about the state of the other. Einstein famously called this “spooky action at a distance” and was deeply uncomfortable with it — but it has been experimentally verified countless times.
Entanglement allows quantum computers to link qubits together in ways that create vastly more computational power than classical systems.
What Is Quantum Interference?
The third key tool is interference. Quantum algorithms are cleverly designed to amplify the probability of correct answers and cancel out wrong ones — similar to how noise-cancelling headphones work, but for calculations.
Together, superposition, entanglement, and interference are what make quantum computers powerful — not raw speed, but the ability to explore many possible solutions simultaneously and zero in on the right one.
What Can Quantum Computers Do?
Quantum computers are not better at everything — they are dramatically better at specific types of problems:
- Drug discovery and molecular simulation: Simulating how molecules interact at the quantum level — something classical computers can barely do — which could lead to breakthrough medicines
- Cryptography: A powerful enough quantum computer could theoretically break current encryption methods (which is why governments and tech companies are developing quantum-resistant encryption now)
- Optimisation problems: Finding the most efficient route through millions of variables — useful for logistics, finance, and AI training
- Machine learning: Accelerating certain AI training processes that are prohibitively slow on classical hardware
Where Are We Now?
Quantum computing is still in its early stages. Current quantum computers — from IBM, Google, Microsoft, and others — are noisy, error-prone, and require extreme cooling (near absolute zero, colder than deep space) to function.
In 2019, Google claimed quantum supremacy — performing a specific calculation in 200 seconds that would take a classical supercomputer 10,000 years. IBM disputed the figure, but it was a landmark moment.
In 2024, Microsoft announced a new type of qubit called a topological qubit, which is inherently more stable and less error-prone. IBM’s roadmap targets fault-tolerant quantum computing by the late 2020s.
A practical, general-purpose quantum computer that outperforms classical computers across a wide range of tasks — sometimes called a cryptographically relevant quantum computer — is likely still a decade or more away.
Should You Be Worried About Quantum Hacking?
Current encryption (like the RSA algorithm that secures most of the internet) is safe for now. But governments and cybersecurity experts are taking the long-term threat seriously. The US National Institute of Standards and Technology (NIST) finalised its first quantum-resistant encryption standards in 2024, and organisations are already beginning the slow process of upgrading their systems.
The Bottom Line
Quantum computers do not work by being faster versions of regular computers. They work by exploiting the strange rules of quantum mechanics — superposition, entanglement, and interference — to explore solutions to problems in ways classical computers simply cannot. They are not going to replace your laptop anytime soon, but for specific, complex problems, they promise to be transformative.
