In 1982, Richard Feynman stood up at the Massachusetts Institute of Technology and made an argument that sounds almost backwards. Ordinary computers, he said, are terrible at imitating quantum systems, because the resources they need balloon exponentially as the system grows. So why not build the computer out of quantum mechanics itself?
Here’s what it means in plain terms. A normal bit is a 0 or a 1. A qubit can be both at once, the way a coin spinning in the air is neither heads nor tails until it lands. Link qubits together through entanglement, and the state of one affects another no matter how far apart they are.
Ideas first, hardware later
Three years after Feynman, David Deutsch proposed what he called a universal quantum computer. In theory it could do any calculation a classical machine can, and for some problems do it exponentially faster.
The 1990s gave the idea teeth. In 1994 Peter Shor published an algorithm that factors large numbers exponentially faster than any classical method. That matters because much of modern encryption leans on factoring being hard, and Shor’s result put a target on it. Two years later Lov Grover came up with a search method for unstructured data that is quadratically faster than the classical approach.
Then came the lab work.
In 2001, IBM and Stanford University ran Shor’s algorithm on a 7-qubit machine. It factored the number 15. A schoolchild can do that in their head, but it was the first tangible proof that a quantum computer could carry out the procedure. Around the same period, companies such as D-Wave Systems began building quantum hardware for a living.
Why it is still hard
Qubits are fragile. Stray interaction with the environment makes them lose their quantum state, a problem called decoherence, and error rates climb as machines get bigger. Quantum computers also need extremely low temperatures, which means heavy cryogenic equipment. Researchers are working on error correction, topological qubits and better isolation, but fault-tolerant computing is still an open pursuit.
In 2019, Google claimed it had reached quantum supremacy, meaning its quantum machine beat classical computers on a specific task. IBM and Microsoft now let the public use quantum systems through the cloud.
The practical upshot: scaling from a handful of qubits to thousands or millions is the job that decides whether any of this reaches everyday use.
