ELI5: what is the difference between quantum computing and classical computing

Imagine classical computers are like a light switch that can be either on or off, while quantum computers are like a dimmer switch that can be on, off, or anything in between.

Think of it this way:

• Classical computing is like having a single light switch. You can only have it either ON (representing a "1") or OFF (representing a "0"). If you have lots of light switches, you can represent complex things, but each switch is only ever ON or OFF at any one time. Imagine trying to find the best route home from school. A classical computer would try each route one at a time: "Is this the best? No. Is THIS the best? No." It has to check every single option individually.

• Quantum computing is like having a special dimmer switch. It can be ON, OFF, or anywhere in between. This "in-between" state is called a superposition. It's like the switch is BOTH on AND off at the same time! This means a quantum computer can explore many possibilities simultaneously. Using the route-finding example, a quantum computer can look at ALL the routes home at the same time. This is because the "switch" can be partially on for one route, and partially on for another.

• Another important concept is entanglement. Imagine you have two of these special dimmer switches, and they're linked together in a magical way. When you change one, the other instantly changes too, no matter how far apart they are! This lets quantum computers perform complex calculations much faster than classical computers.