Decoherence of many-spin systems in NMR: From molecular characterization to an environmentally induced quantum dynamical phase transition

TL;DR

This paper investigates decoherence in many-spin systems using NMR, employing advanced quantum master equations and Keldysh formalism, revealing an environmentally induced quantum dynamical phase transition with implications for quantum control and molecular characterization.

Contribution

It introduces a comprehensive approach combining Liouville-von Neumann and Keldysh formalisms to analyze decoherence, leading to new insights into quantum phase transitions in open systems.

Findings

Identification of an environmentally induced quantum dynamical phase transition

Validation of theoretical models with Nuclear Magnetic Resonance experiments

Development of new numerical methods for quantum system analysis

Abstract

The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.