Topics on the information theoretic limits of quantum information processing and its implementation
Year: 2015
Type: dissertation
Abstract: Recent advances in quantum technologies enabled us to make large quantum states \nand pushed towards examining quantum theory at the macroscopic level. However observation \nof quantum e ects at a macroscopic level still remains a demanding task. In this \nthesis we try to address one of the challenges and propose and explore some new solutions. \nOne of the obstacles for observation of macroscopic quantum e ects is the sensitivity \nto the measurement resolution. For many di erent cases, it has been observed that the \nprecision requirement for measuring quantum e ects increases with the system size. We \nformalize this as a conjecture that for observation of macroscopic quantum e ects, either \nthe outcome precision or the control precision of the measurements has to increase with \nsystem size. This indicates that the complexity of macroscopic quantum measurement \nincreases with the system size and sheds some lights on the quantum-to-classical transition \nat the macroscopic level. \nWe also introduce a technique to go around the sensitivity problem for observation \nof micro-macro entanglement. We propose that using a unitary deampli cation process, \none can bring the system back to the microscopic level where the measurements are less \ndemanding and quantum e ects are easier to verify. As the unitary processes do not change \nthe entanglement, this serves as a veri cation tool for micro-macro entanglement. \nWe also explored the connection between quantum e ects and thermodynamics of \nmacroscopic quantum systems for two speci c cases. For one, we investigated the e ect of \nentanglement in composite bosons and Bose-Einstein condensation. We showed that as the \nstate of the composite boson approaches a maximally entangled state, the condensation \nrate also approaches one. \nThe other case we considered was heat-bath algorithmic cooling. We found the cooling \nlimit of this class of thermodynamic transformations and showed that it decreases \nexponentially with the number of qubits. \nWe also developed an entropic version of Mermin's inequality. Here the idea is to \ndevelop a tool to reveal the entanglement in many-body quantum systems based on the \nentropy of the measurement outcomes. We introduce a new inequality that holds for locally \nrealistic models, yet can be violated with quantum measurements. One of the nice features \nof this inequality is that it can be violated maximally with quantum measurements. This \nresembles the GHZ paradox but for entropies of the measurement outcomes.
Source: UWSpace (University of Waterloo)
Author: Sadegh Raeisi
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W1747755655