# What is quantum fidelity?

There is a term called “quantum fidelity.”

Quantum computers are analog computers, after all — the qubit can take 0 or 1 or any value in between. In contrast, normal computers are digital (0 or 1).

A quantum computer could assume a real number, say a value with 1 / sqrt(2) = 0.707107 … probability of assuming zero, for example. An irrational real number has infinite spaces after the comma.

However, imagine that the computer is a bunch of devices that control electromagnetic waves. This will have finite precision.

You’ll have to stop somewhere after the comma. This goes for any analog computer.

This difference between the actual number and the accuracy of the real computer is the quantum fidelity.

It is a different kind of error than decoherence. The decoherence error is the atom being in a superposition, interacting with the environment (a ray of light, an interference), and collapsing to 0 or 1.

Join my quantum computing study group in Facebook:

See also:

https://quantumcomputing.stackexchange.com/questions/6733/what-does-fidelity-mean

How to encode the complete works of Machado de Assis in a single number