A quantum algorithm, like a sword stroke, must be repeated until the solution is certain.

### Definition/Summary:

Mathematics

- An imaginary or complex number system that is used to help evaluate the square roots of negative numbers or other more complicated mathematic problems
- When solving an equation the answer might be that there are no real solutions, yet there might be complex solutions to the problem

Quantum algorithm

- Runs on a realistic model of quantum computation, which is the theoretical computation systems most commonly used within a quantum circuit model of computation
- Used as a circuit model of quantum computation, by a quantum circuit which is a much smaller circuit than classical circuitry, it acts on inputs of qubits and terminates with a measurement
- A quantum circuit consists of simple quantum gates which act on at most a fixed number of qubits
- The term quantum algorithm is usually used for those algorithms which seem inherently quantum, or use some essential feature of quantum computation such as quantum superposition or quantum entanglement

A classical (or non-quantum) algorithm is a finite sequence of instructions, or a step-by-step procedure for solving a problem, where each step or instruction can be performed on a classical computer