Protecting subspaces by acting on the outside

TL;DR

This paper explores methods to maintain quantum systems within a desired subspace by applying strong external interactions and leveraging dissipation, inspired by toy models and the quantum Zeno effect.

Contribution

It introduces strategies for protecting quantum subspaces using outside interactions and dissipation, expanding on existing quantum control techniques.

Findings

Strong outside interactions can effectively keep systems within target subspaces.

Dissipation can be constructively used to enhance subspace protection.

Analogies to toy models and the quantum Zeno effect provide valuable insights.

Abstract

Many quantum control tasks aim at manipulating the state of a quantum mechanical system within a finite subspace of states. However, couplings to the outside are often inevitable. Here we discuss strategies which keep the system in the controlled subspace by applying strong interactions onto the outside. This is done by drawing analogies to simple toy models and to the quantum Zeno effect. Special attention is paid to the constructive use of dissipation in the protection of subspaces.