Classical computers store information as bits — 0 or 1. Quantum computers use qubits, which exploit two quantum mechanical phenomena: superposition and entanglement.
Superposition A qubit in superposition is not 0 or 1 — it is a probability distribution over both states simultaneously. Only when measured does it collapse to a definite value. This means a quantum processor with n qubits can represent 2ⁿ states at once.
Entanglement Two entangled qubits share a correlated quantum state. Measuring one instantly determines the state of the other, regardless of distance. This non-classical correlation is what allows quantum algorithms to process certain problems in ways no classical system can replicate.
What Can It Actually Do? Quantum computers are not universally faster. For most everyday tasks — browsing the web, running Excel — a classical chip is faster, cheaper, and more practical.
Quantum advantage is real for specific problem classes: - Factoring large integers (Shor's algorithm) — threatens RSA encryption - Searching unsorted databases (Grover's algorithm) — quadratic speedup - Simulating quantum systems (chemistry, materials) — exponential speedup - Optimization problems — potential but less proven speedup
Where Are We Now? In 2019, Google claimed quantum supremacy on a specific sampling problem. IBM, IonQ, and Quantinuum have since built systems with 100–1000+ qubits. But raw qubit count is misleading — error rates matter more. Today's systems are NISQ (Noisy Intermediate-Scale Quantum) devices. Fault-tolerant quantum computing, which requires error correction and millions of physical qubits per logical qubit, is still years away.
The Threat to Encryption Post-quantum cryptography is already being standardized by NIST. Governments and companies are upgrading encryption protocols now — before large-scale quantum computers exist — because adversaries can harvest encrypted data today and decrypt it later.
Quantum computing will not replace classical computing. But for chemistry simulation, optimization, and cryptography, it will be transformative.