Enforcing nonclassicality in medium-scale quantum systems

Abstract

This thesis investigates three aspects of nonclassicality.

The first aspect is macroscopic quantumness, a field which considers the properties of macroscopic superpositions. The various measures of macroscopicity are reviewed. An optomechanical system is described which enables us to study nonclassicality in macroscopic mechanical oscillators. We analyse the impact of different measurement settings on the macroscopicity of the mirror and the Wigner functions of the mechanical state. The same system is also considered under open system dynamics.

The second nonclassical concept is the violation of macrorealism. It is shown that a two-level system can violate the Leggett-Garg inequality, thereby demonstrating that the assumptions of macrorealism do not hold. Similar dynamics are then replicated in a macroscopic mechanical system through the use of a hybrid optomechanical system in which an atom interacts with the mechanical oscillator through an optical mode. Mechanical damping is then factored into the dynamics to examine its effect on the violation of the Leggett-Garg inequality for different parameter ranges.

The third is nonclassical correlations. Quantum discord and quantum entanglement are defined and several measures are explained. Entanglement distribution via separable states is introduced and then built on by adding imperfections to the operations in the protocol. It is found that the protocol is still successful in spite of the errors in the operations, both when they are unitary and non-unitary. We also develop a method of generating entanglement between two bosons through mediation with two spin systems. Through this system we demonstrate the creation of both entangled coherent states and NOON states.

Date of Award	Jul 2022
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Mauro Paternostro (Supervisor) & Alessandro Ferraro (Supervisor)