In this chapter, we shall discuss some practical applications of quantum control and dynamics. Our goal is not to give an exhaustive introduction to areas of application, but to point out the role of control and dynamics so as to further motivate the field as well as the techniques described in the previous chapters. The basics of mathematical modeling of quantum mechanical control systems were described in Chapter 2. Here we focus on more practical aspects in the areas of nuclear magnetic resonance and control of molecular and atomic systems. We also discuss a possible implementation of quantum information processing, namely the one with trapped ions. The dynamics here is used to implement quantum logic gates. We shall show how, changing the physical set-up, it is possible to create different Hamiltonians. The control is obtained by switching among these different Hamiltonians.
In this chapter, we shall discuss some practical applications of quantum control and dynamics. Our goal is not to give an exhaustive introduction to areas of application, but to point out the role of control and dynamics so as to further motivate the field as well as the techniques described in the previous chapters. The basics of mathematical modeling of quantum mechanical control systems were described in Chapter 2. Here we focus on more practical aspects in the areas of nuclear magnetic resonance and control of molecular and atomic systems. We also discuss a possible implementation of quantum information processing, namely the one with trapped ions. The dynamics here is used to implement quantum logic gates. We shall show how, changing the physical set-up, it is possible to create different Hamiltonians. The control is obtained by switching among these different Hamiltonians.
This chapter discusses some practical applications of quantum control and dynamics. It focuses on more practical aspects in the areas of nuclear magnetic resonance and control of molecular and atomic systems. The chapter discusses a possible implementation of quantum information processing, namely the one with trapped ions. It shows how, changing the physical set-up, it is possible to create different Hamiltonians. The motion of the electrons around the nucleus creates a magnetic field which opposes the constant external magnetic field. This magnetic field will be different according to the environment of the nucleus under consideration and the chemical bonds with the neighboring nuclei. It will result in a change in the Larmor frequency which is called chemical shift. The Larmor frequency is always proportional to the external field in the z direction, but the proportionality constant changes because of the chemical shift.
The role of trapped atomic ions in the field of quantum information processing is briefly reviewed. We discuss some of the historical developments that enabled ions to enter the field and then summarize the basic mechanisms required for logic gates and the use of the gates in demonstrating simple algorithms. We describe potential pathways to reach fault-tolerant error levels and large-scale devices, and highlight some of the main problems that will be faced in achieving these goals. Possible near-term applications in applied and basic science, such as in metrology and quantum simulation, are discussed.
The introduction of control theory in quantum mechanics has created a rich, new interdisciplinary scientific field, which is producing novel insight into important theoretical questions at the heart of quantum physics. Exploring this emerging subject, Introduction to Quantum Control and Dynamics presents the mathematical concepts and fundamental physics behind the analysis and control of quantum dynamics, emphasizing the application of Lie algebra and Lie group theory. To advantage students, instructors and practitioners, and since the field is highly interdisciplinary, this book presents an introduction with all the basic notions in the same place. The field has seen a large development in parallel with the neighboring fields of quantum information, computation and communication. The author has maintained an introductory level to encourage course use. After introducing the basics of quantum mechanics, the book derives a class of models for quantum control systems from fundamental physics. It examines the controllability and observability of quantum systems and the related problem of quantum state determination and measurement. The author also uses Lie group decompositions as tools to analyze dynamics and to design control algorithms. In addition, he describes various other control methods and discusses topics in quantum information theory that include entanglement and entanglement dynamics. Changes to the New Edition: New Chapter 4: Uncontrollable Systems and Dynamical Decomposition New section on quantum control landscapes A brief discussion of the experiments that earned the 2012 Nobel Prize in Physics Corrections and revised concepts are made to improve accuracy Armed with the basics of quantum control and dynamics, readers will invariably use this interdisciplinary knowledge in their mathematics, physics and engineering work.
Solid-state nuclear magnetic resonance (NMR) has emerged as an important technique for material characterization, finding extensive applications across a diverse range of disciplines including physics, materials science, chemistry, and biology. Its utility stems from the ability to probe the local atomic environments and molecular dynamics within solid materials, which provides information on the composition of the material. In recent years, the scope of solid-state NMR has expanded into the realm of quantum information science and technology, where its abundant many-body interactions pulse control methodologies make it have significant research value and application potential. This paper offers a comprehensive overview of the research objects and theoretical underpinnings of solid-state NMR, delving into the critical nuclear spin interaction mechanisms and their corresponding Hamiltonian forms. These interactions, which include dipolar coupling, chemical shift anisotropy, and quadrupolar interactions, are fundamental to the interpretation of NMR spectra and the understanding of material properties at the atomic level. Moreover, the paper introduces typical dynamical control methods employed in the manipulation of solid-state nuclear spins. Techniques such as dynamical decoupling, which mitigates the effects of spin-spin interactions to extend coherence times, and magic-angle spinning, which averages out anisotropic interactions to yield high-resolution spectra. These methods are essential for enhancing the sensitivity and resolution of NMR experiments, enabling the extraction of detailed structural and dynamic information from complex materials. Then we introduce some recent advancements in quantum control based on solid-state NMR, such as nuclear spin polarization enhancement techniques, which include dynamic nuclear polarization (DNP) and cross polarization (CP), significantly boost the sensitivity of NMR measurements. Additionally, the control techniques of Floquet average Hamiltonians are mentioned, showcasing their role in the precise manipulation of quantum states and the realization of quantum dynamics. Finally, the paper presents a series of seminal research works that illustrate the application of solid-state NMR quantum control technologies in the field of quantum simulation. These studies demonstrate how solid-state NMR can be leveraged to simulate and investigate quantum many-body systems, providing valuable insights into quantum phase transitions, entanglement dynamics, and other phenomena relevant to quantum information science. By bridging the gap between fundamental research and practical applications, solid-state NMR continues to play a crucial role in advancing our understanding of quantum materials and technologies.
Fifty years of developments in nuclear magnetic resonance (NMR) have resulted in an unrivaled degree of control of the dynamics of coupled two-level quantum systems. This coherent control of nuclear spin dynamics has recently been taken to a new level, motivated by the interest in quantum information processing. NMR has been the workhorse for the experimental implementation of quantum protocols, allowing exquisite control of systems up to seven qubits in size. This article surveys and summarizes a broad variety of pulse control and tomographic techniques which have been developed for, and used in, NMR quantum computation. Many of these will be useful in other quantum systems now being considered for the implementation of quantum information processing tasks.
In this paper we survey some results in Control Theory that have had a significant impact on quantum mechanics and its applications. We shall consider three specific examples: 1) The concept of controllability, in its various forms, has provided a practical test to verify the feasibility of a number of putative experiments in quantum physics. The verification of controllability involves the study of the Lie algebra structure underlying the system. This study itself has proved a valuable tool to design experiments. 2) Results on the uniform generation of compact Lie groups have been applied to show that almost every set of quantum gates is universal for quantum computation. This result can be further refined by showing that the number of gates necessary to implement quantum logic operations is uniformly bounded by a value which only depends on the number of quantum bits processed. 3) Techniques of Optimal Control Theory have been employed to show that the pulses used to drive particles with spin 1/2 in Nuclear Magnetic Resonance are the optimal pulses which minimize the time of state transfer (subject to an energy constraint) and the energy (subject to a time constraint).