Quantum Computing
A classical bit is binary, it can take on one of the two states, state 0 or state 1, say absence of a voltage at a transistor gate or presence of a voltage on that gate. These are discrete, robust states, and when we measure the state of that transistor we will either get 0 or 1.
A quantum computer is built from logical elements called qubits, quantum bits. A qubit is also binary in the sense that it is realized using a quantum two-state system, which can be set to state 0 or state 1.
Since qubits are quantum mechanical, it can do much more. A qubit can be in superposition of states, i.e. a single qubit can carry aspects of both state 0 and state 1 simultaneously. This is a manifestation of a quantum mechanical effect.Superposition lets one qubit perform two calculations at once, two qubits perform 2^2 = 4 calculations simultaneously, 3 qubits 8 calculations, and so on. Another quantum mechanical effect, called entanglement is also utilized. A 50 qubit system can perform more calculations than the largest supercomputer available on the earth.