Quantum Computers: How They Work, What They Could Do and Why They Are So Difficult to Build

Quantum computers are fundamentally different from the classical computers we use every day; they are not simply faster or more powerful versions of laptops or supercomputers. Classical computers process information using bits that have a definite value of either 0 or 1. Quantum computers use quantum bits, or qubits, which can be built from physical systems such as photons, trapped ions, neutral atoms, electron spins or superconducting electrical circuits.