Quantum Computer
A computer that uses quantum-mechanical phenomena (superposition, entanglement) to perform certain calculations exponentially faster than classical computers.
A quantum computer processes information using qubits — quantum-mechanical analogues of classical bits. Unlike classical bits, which are either 0 or 1, qubits can exist in superposition and can be entangled with other qubits, meaning their states are correlated even at distance.
For a small set of problems — factoring large numbers (Shor's algorithm), simulating quantum systems, certain optimisation problems — quantum computers can theoretically be exponentially faster than classical machines. For most everyday computing, however, classical computers will remain superior indefinitely.
As of 2025, leading quantum computers from IBM, Google, IonQ, and others have demonstrated up to ~1,000 noisy qubits. Useful, fault-tolerant quantum computing requires error correction, which would scale physical qubit counts into the millions.