Optimal Control of Finite Dimensional Quantum Systems

TL;DR

This thesis develops a control theory framework for quantum systems, focusing on the quantum tracking problem, which balances information gain and disturbance, with applications in quantum information processing.

Contribution

It introduces the quantum tracking problem as an optimization framework for quantum control, bridging classical control concepts with quantum measurement challenges.

Findings

Formulated quantum tracking as an optimization problem.

Provided analytical and numerical solutions for quantum state transformation.

Characterized the trade-off between information gain and disturbance.

Abstract

This thesis addresses the problem of developing a quantum counter-part of the well established classical theory of control. We dwell on the fundamental fact that quantum states are generally not perfectly distinguishable, and quantum measurements typically introduce noise in the system being measured. Because of these, it is generally not clear whether the central concept of the classical control theory -- that of observing the system and then applying feedback -- is always useful in the quantum setting. We center our investigations around the problem of transforming the state of a quantum system into a given target state, when the system can be prepared in different ways, and the target state depends on the choice of preparation. We call this the "quantum tracking problem" and show how it can be formulated as an optimization problem that can be approached both numerically and analytically. This problem provides a simple route to the characterization of the quantum trade-off between information gain and disturbance, and is seen to have several applications in quantum information.