The preparation of states in quantum mechanics

TL;DR

This paper discusses methods for preparing specific initial states in quantum systems, highlighting a technique that guarantees success by coupling the system to an environment to steer it towards the desired state.

Contribution

It introduces and analyzes a method for quantum state preparation that ensures certainty by using environment-induced dynamics to reach the target state.

Findings

Method guarantees preparation with probability one

Coupling to environment induces state convergence

Detailed analysis of the environment-assisted preparation process

Abstract

The important problem of how to prepare a quantum mechanical system, $S$, in a specific initial state of interest - e.g., for the purposes of some experiment - is addressed. Three distinct methods of state preparation are described. One of these methods has the attractive feature that it enables one to prepare $S$ in a preassigned initial state with certainty; i.e., the probability of success in preparing $S$ in a given state is unity. This method relies on coupling $S$ to an open quantum-mechanical environment, $E$, in such a way that the dynamics of $S \vee E$ pulls the state of $S$ towards an "attractor", which is the desired initial state of $S$. This method is analyzed in detail.