Physics
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Item Foundational Theoretical Issues of Quantum Heat Engines and Hot Entanglement(2022) Arisoy, Onat; Hu, Bei-Lok; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We study open quantum systems in the contexts of quantum heat engines, refrigerators and quantum entanglement in systems in contact with high temperature reservoirs. Emphasizing the underlying theoretical foundations rather than practical aspects such as enhancement in efficiency of engines and refrigerators or in entanglement measures for a particular set of system and bath parameters, this work focuses on some important aspects of open quantum systems and quantum thermodynamics and provide in-depth analysis of them using relatively simple yet robust models in non- equilibrium statistical mechanics. These examples include a refrigerator for quantum many-body systems in the Markovian regime, a single harmonic oscillator quantum Otto cycle with its generalization to squeezed thermal baths and the entanglement dynamics of two coupled harmonic oscillators each having its own separate thermal baths in the non-Markovian regime. The investigation of these setups in a unified context in this dissertation also brings up the discussion on the validity of Markovian approximation for open quantum systems and the qualitative differences in Markovian versus non-Markovian open system dynamics, which is addressed on multiple occasions throughout the cases we study. Our analysis of quantum Otto cycle with squeezed thermal reservoirs show that the efficiency of the cycle does not change due to the squeezing in the bath in contrast to previous works studying the same cycle restricted by Markovian assumptions. In our investigation of the effects of time-dependent coupling in a system of two harmonic oscillators with two separate baths in both Markovian and non-Markovian regimes, we find that the driving-induced instability of the solutions of the Langevin equations of the oscillator system is necessary to sustain entanglement at late times with hot reservoirs which mayrender hot entanglement untenable. The effects of Markovianity/non-Markovianity, non-thermal reservoirs, contact with multiple reservoirs and time-dependent system Hamiltonians in quantum thermodynamics are addressed in this thesis.Item Multi-Species Trapped Atomic Ion Modules for Quantum Networks(2016) Inlek, Ismail Volkan; Monroe, Christopher R; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trapped atomic ions are among leading platforms in quantum information processing with their long coherence times and high fidelity quantum operations. Scaling up to larger numbers of qubits is a remaining major challenge. A network of trapped ion modules offers a promising solution by keeping a manageable number of qubits within a module while photonic interfaces connect separate modules together to increase the number of controlled memory qubits. Since the generation of entanglement between qubits in different modules is probabilistic, an excessive number of connection trials might result in decoherence on the memory qubits through absorption of stray photons. This crosstalk issue could be circumvented by introducing a different atomic species as photonic qubits. Compared to a system that only utilizes single species of atoms, there are also additional advantages in a multi-species apparatus where attractive features of each atom can be employed for certain tasks. In this thesis, I present experimental demonstrations of necessary ingredients of a multi-species module for quantum networking. In these experiments, barium ions are intended to be used as photonic communication qubits with visible photon emission lines that are more convenient for current fiber optics and detector technologies while ytterbium ions are used for storing and processing quantum information where long coherence times available in hyperfine clock states make them suitable memory qubits. The key experiments include demonstration of atom-photon entanglement using the barium qubit and utilizing the Coulomb interaction between ytterbium and barium with spin-dependent forces for transfer of information from communication to memory qubits.Item Control and Verification of Quantum Mechanical Systems(2015) Kafri, Dvir; Taylor, Jacob M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quantum information science uses the distinguishing features of quantum mechanics for novel information processing tasks, ranging from metrology to computation. This manuscript explores multiple topics in this field. We discuss implementations of hybrid quantum systems composed of trapped ions and superconducting circuits, protocols for detecting signatures of entanglement in small and many-body systems, and a proposal for ground state preparation in quantum Hamiltonian simulators.