Physical and logical qubits
In quantum computing, a qubit is a unit of information analogous to a bit (binary digit) in classical computing, but it is affected by quantum mechanical properties such as superposition and entanglement which allow qubits to be in some ways more powerful than classical bits for some tasks. Qubits are used in quantum circuits and quantum algorithms composed of quantum logic gates to solve computational problems, where they are used for input/output and intermediate computations.
Quantum computing
A quantum computer operates on its qubits using quantum gates and measurement (which also alters the observed state). An algorithm is composed of a fixed sequence of quantum logic gates and a problem is encoded by setting the initial values of the qubits, similar to how a classical computer works. The calculation usually ends with a measurement, collapsing the system of qubits into one of the formula_2 eigenstates, where each qubit is zero or one, decomposing into a classical state. The outcome can, therefore, be at most formula_1 classical bits of information. If the algorithm did not end with a measurement, the result is an unobserved quantum state. (Such unobserved states may be sent to other computers as part of distributed quantum algorithms.)