Quantum States and Quantum Computers

Before we discuss the details of quantum states, it might be helpful to have an overview of how a quantum computer works. As shown in the figure below, reading from left to right, we start with a system of qubits (objects) in some specified quantum state. The qubits then interact with a collection of quantum gates, and then each qubit interacts with a measurement device, permitting the analysis of results. That is, in most QC and QIS situations, we “prepare” a system in some quantum state, act on it with quantum gates, and “measure” the resulting state.