We present the implementation of the Bohmian hydrodynamic formulation of quantum mechanics to the description of electron dynamics in one-dimensional laser-atom interaction. The resulting quantum trajectories clearly picture the dynamics and yield an accurate description of observables.
This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explains the historical development of Bohmian mechanics, Bohmian mechanics for single particle and for many particle systems. It discusses the dynamics of a single hydrogen atom interacting with a strong laser and presents a clear example on how a Bohmianthinking on superluminal velocities and nonlocal interactions helps in extending the quantum theory towards relativity and quantum field theory. The book also explains model nanoscale electron devices and their Bohmiancomputing development for knowing the ab initio quantum mechanical structure, energetics and thermodynamics of multiatoms systems. It deals with new cosmological models describing the accelerating universe in the spatially flat case. The book describes how many conceptual problems that appear in a description of gravity in quantum mechanical terms, such as the measurement problem and the problem of time, can be overcome by adopting a Bohmian perspective.
Bohmian mechanics as formulated originally in 1952, has been useful in the implementation of numerical methods applied to quantum mechanics. The scientific community though has had ever since a critical thought about it. Therefore, there are still points to be clarified and rectified. The two main problems are basically: Bohmian mechanics gives a privilege role to the position representation. Secondly, the current interpretation of Bohmian trajectories has been recently proven wrong. In this context, in Chapter 2, new complex Bohmian quantities are defined; so that they allow the capacity to formulate Bohmian mechanics in any arbitrary continuous representation, for instance, the momentum representation. This Chapter is fully based on two articles, regarding the proposed complex Bohmian formulation and its extension into momentum space. Chapter 3 deals with a redefinition and reinterpretation of the Bohmian trajectories from the handling of the continuity equation, this is done without any need of additional postulates or interpretations. Also, it is proved that Bohmian mechanics is actually more than a projective aspect of the Wigner function. As a third point, Chapter 4 presents a sytematic treatment of the hydrodynamic scheme of Bohmian mechanics. Then, a brief summary of the transport equations in Bohmian mechanics is done. Next, a unified hydrodynamic treatment is found for the Bohmian mechanics. This treatment is useful to sketch, a Bohmian treatment to efficiently find the steady value of the transmission integral. In Chapter 5 conclusions of this thesis are drawn.
In the last few years the hydrodynamic formulation of quantum mechanics, equivalent to the Bohmian equations of motion, has been used to obtain numerical solutions of the Schrodinger equation. Problems, however, have been experienced near wave function nodes (or low probability regions). Here we attempt to compute wave functions and Bohmian trajectories for the interference of one particle or of two identical particles. It turns out that the large number of nodes (i.e. interference minima) makes the hydrodynamic equations impractical, whereas a more straightforward solution of the Schrodinger equation gives very good results.
A new approach to the coupling of quantum and classical dynamics is developed, by combining a hydrodynamic, Bohmian description for the quantum subsystem with a Liouville-space description for the classical subsystem. To this end, partial hydrodynamic moments are introduced, the dynamics of which is determined by a hierarchy of equations derived from the quantum Liouville equation. We focus on pure states (wave functions) and introduce a trajectory representation in a hybrid hydrodynamic-Liouvillian phase space. The interleaved trajectory dynamics is guided by a new type of quantum force. For illustration, we consider a pair of bilinearly coupled harmonic oscillators, for which the method is exact.
The ontological interpretation of Bohmian quantum mechanics, through a particle's visual trajectory of motion, reconstitutes realism and determinism (and thus causality) in a quantum system. There also exists a similar but distinctive class of interpretation under Bohmian quantum mechanics, called the hydrodynamical interpretation. Here, the trajectories of the probability fluid flow play a significant computational role. The flow of the probability density visually helps chemists and engineers to solve the corresponding quantum hydrodynamical equations of motion. This particular computational scheme for the numerical solutions is called ‘the quantum trajectory method.' The success of the quantum trajectory method demonstrates the power of visual illustrations and metaphors in representing and analyzing quantum systems.