Abstract

Single molecule magnets are novel mesoscopic materials exhibiting both classical and quantum qualities. Revealing the decoherence and entanglement mechanisms during these systems is vital for that applications in quantum information technologies. Within this thesis, quantum tunneling of magnetization is studied in single molecule magnet dimer [Mn4]2. Motivated through the recent experiments demanding the alteration of the present theories, phonon mediated spin bath decoherence model is suggested. In part one from the thesis, the magnetization from the [Mn4]2 dimer under exterior magnetic field is investigated. Alternative entangled spin states involved with quantum tunnelings are identified by way of the precise solution from the Schrdinger equation and also the Landau-Zener-Stckelberg method. Later, a decoherence model is introduced where the interaction between your single molecule magnet (central spin) and spin bath is mediated by phonons inside a coherent condition or thermal distribution. It’s observed the decoherence factor decays inside a Gaussian fashion also it becomes in addition to the phonon frequencies at short occasions for coherent states and occasional temperature thermal distribution. Within the former situation, when the phonon powers tend to be bigger than spin-phonon coupling or bath spins are fully polarized, decoherence time becomes in addition to the initial phonon condition. For that thermal condition situation, phonons play more essential role in decoherence with growing temperature. Potential side effects from the temperature on spin bath contribution to decoherence is discussed. Then, the result of entangled atmosphere on decoherence is examined.

Entanglement within atmosphere is proven to lessen the decoherence of central spin. Also, the entanglement dynamics from the central bipartite spin product is studied. Classification from the Bell states is examined for common spin bath, and separate spin baths. Last area of the thesis may be the analysis of dephasing in entangled qutrits (three level quantum systems) underneath the classical noise, and quantum decoherence. Density matrix formalism is proven to provide equivalent recent results for both cases. For common and separate baths, robust and fragile Bell-like qutrit states were determined, and Horodecki’s bound entangled condition is proven to become better quality to decoherence within the latter situation.

Decoherence. — Entanglement. — Quantum tunneling. — Single molecule magnet. — Spin bath. — Phonon. — Quantum computers. — Tunelling. — Spin-spin interaction. — Phonons. — Eevresizlik. — Dolaklk. — Kuantum tnnellemesi. — Tek molekl mknats. — Spin banyosu. — Fonon. — Kuantum bilgisayarlar. — Tnelleme. — Spin-spin etkilemesi. — Fononlar.

Electron transport in single molecule magnet transistors and optical transitions within the 15N-V- center in gemstone

This thesis presents theoretical studies coping with quantum interference effects in electron transport through single molecule magnet transistors along with a study optical Λ transitions within the 15 NV – center in gemstone.

The thesis begins with a short general summary of the physics of quantum transport through single electron transistors. Later on, the primary body from the thesis is split into three studies: (i) In chapter (2) we describe the qualities of single molecule magnets and also the Berry phase interference contained in these nanomagnets. Then we propose a method to identify quantum interference experimentally in the present of merely one molecule magnet transistor using polarized leads. We apply our theoretical leads to the recently synthesized nanomagnet Ni4. (ii) In chapter (3) we evaluate the Kondo effect and offer a microscopic derivation from the Kondo Hamiltonian appropriate for full and half-integer spin nanomagnets. Then we calculate the conductance from the single molecule magnet transistor in the existence of the Kondo effect for Ni4 and show the way the Berry phase interference becomes temperature dependent. (iii) We conclude in chapter (4) having a theoretical study from the single Nitrogen vacancy defect center in gemstone. We reveal that you’ll be able to have spin non-conserving transitions through the hyperfine interaction and propose a method to write and browse quantum information using circularly polarized light by way of optical Λ transitions within this solid condition system.

Michael N. Leuenberger

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