Topics on the information theoretic limits of quantum information processing and its implementation

Quantum Information;Quantum mechanics;Quantum Computation;Classical-to-Quantum transition;Quantum thermodynamics;Heat-bath algorithmic cooling;Quantum cloning;macroscopic quantum effect;Physics (Quantum Information)

Raeisi, Sadegh

University of Waterloo

关键词: Quantum Information;    Quantum mechanics;    Quantum Computation;    Classical-to-Quantum transition;    Quantum thermodynamics;    Heat-bath algorithmic cooling;    Quantum cloning;    macroscopic quantum effect;    Physics (Quantum Information);   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/9195/3/Raeisi_Sadegh.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Recent advances in quantum technologies enabled us to makelargequantum statesand pushed towards examining quantum theory at the macroscopic level. However observationof quantum e ects at a macroscopic level still remains a demanding task. In thisthesis we try to address one of the challenges and propose and explore some new solutions.One of the obstacles for observation of macroscopic quantum e ects is the sensitivityto the measurement resolution. For many di erent cases, it has been observed that theprecision requirement for measuring quantum e ects increases with the system size. Weformalize this as a conjecture that for observation of macroscopic quantum e ects, eitherthe outcome precision or the control precision of the measurements has to increase withsystem size. This indicates that the complexity of macroscopic quantum measurementincreases with the system size and sheds some lights on the quantum-to-classical transitionat the macroscopic level.We also introduce a technique to go around the sensitivity problem for observationof micro-macro entanglement. We propose that using a unitary deampli cation process,one can bring the system back to the microscopic level where the measurements are lessdemanding and quantum e ects are easier to verify. As the unitary processes do not changethe entanglement, this serves as a veri cation tool for micro-macro entanglement.We also explored the connection between quantum e ects and thermodynamics ofmacroscopic quantum systems for two speci c cases. For one, we investigated the e ect ofentanglement in composite bosons and Bose-Einstein condensation. We showed that as thestate of the composite boson approaches a maximally entangled state, the condensationrate also approaches one.The other case we considered was heat-bath algorithmic cooling. We found the coolinglimit of this class of thermodynamic transformations and showed that it decreasesexponentially with the number of qubits.We also developed an entropic version of Mermin;;s inequality. Here the idea is todevelop a tool to reveal the entanglement in many-body quantum systems based on theentropy of the measurement outcomes. We introduce a new inequality that holds for locallyrealistic models, yet can be violated with quantum measurements. One of the nice featuresof this inequality is that it can be violated maximally with quantum measurements. Thisresembles the GHZ paradox but for entropies of the measurement outcomes.