Examensarbeten för masterexamen // Master Theses
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Browsar Examensarbeten för masterexamen // Master Theses efter Ämnesord "Atom- och molekylfysik och optik"
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- PostCapturing radon on tobacco smoke(2011) Sanden, Magnus; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceRadon is one of the largest causes for lung cancer in the world. In fact, it is second only to smoking. It has been observed that tobacco smoking increases the risks of radon-induced lung cancer, but there does not appear to be any theory that quantitatively describes why this is. This thesis is a study of a possible reason for this increase in mortality. I have investigated if and how radon atoms adsorb onto some molecules present in tobacco smoke and other types of smoke. My study can therefore also help to develop an understanding of possible radon-associated health effects that may follow from enjoying an open replace. If radon does adsorb onto the smoke it may increase the likelihood of these radioactive atoms decaying in the lungs and depositing their daughter nuclei there. Most of the daughter nuclei are radioactive and of them at least lead is also toxic. The investigation was done through electronic structure calculations using density functional theory. I have chosen a non-empirical method because there are not many experiments on radon interactions. The van der Waals density functional was used to account for the van der Waals interactions. Adsorbtions of between 70 meV and 156 meV were found on all investigated molecules from the smoke. Large polycyclic aromatic hydrocarbons gave the strongest adsorbtion. In a trend study with different noble gas atoms, bigger atoms adsorbed more strongly, including radon which adsorbed most strongly. The thesis includes an overview of the theory behind the density functional theory used in the calculations.
- PostEncoding of Qubit States in Resonators With Cat Codes(2019) Winther, Johan; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceQuantum computing has gained a lot of interest in recent years and commercial products are just now entering the market. However one of the main challenges in realising a quantum computer is noise and one key technology to remedy this is quantum error correction (QEC). One way of performing QEC exploits the storage of the quantum information of a qubit in a resonator as cat codes. To do this one needs to apply encoding pulses to the coupled qubit-resonator system in order to perform a state transfer from the qubit to the resonator. These pulses need to be numerically obtained by simulation. This thesis studies the potential of using a gradient-based optimization method, the so called Krotov's method, to numerically optimize encoding pulses for encoding arbitrary qubit states in cat codes. The Python package Krotov, a package for quantum optimal control using the method, is first used to perform state evolution from |0> to |1> and |0> to |2> of an anharmonic resonator in order to familiarise with the package and optimal control in general. It is shown that, assuming a maximum drive amplitude and no dissipation, the method can realise a |0> to |1> evolution with fidelity F > 0.99999 and a total pulse length of only 10.75 ns. For the |0> to |2> evolution a total pulse length of 30 ns is needed to reach the same fidelity. Finally, the Krotov is used to optimize pulses for transferring qubit states into the resonator as cat codes. The transfer of six states were simultaneously optimized in order to approximate a unitary which transfers an arbitrary qubit state into the resonator as a cat code. Using mostly experimentally realistic parameters, it is shown that the method can optimize pulses which realise the encoding of arbitrary qubit states to cat codes with a fidelity of at least F > 0.998900. Although plenty of challenges still remain to prove this can be done in experiments, the results points to the Krotov package as a viable tool for encoding pulse optimization.
- PostHydrogen adsorption on graphene and coronene: A van der Waals density functional study(2011) Varenius, Eskil; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceThis thesis investigates hydrogen adsorption on graphene and coronene within the framework of density functional theory. The new nonlocal van der Waals density functional (vdW-DF) method is used: the original version, vdW-DF1, and the new higher accuracy version, vdW-DF2. Hydrogen adsorption is studied in the context of formation of molecular hydrogen in interstellar space, a process thought to depend on hydrogen adsorbing on a graphitic surface. Calculations were done for hydrogen above coronene and graphene with both vdW-DF1 and vdW-DF2 to investigate how these functionals perform in the case of hydrogen adsorption on a graphitic surface. All calculations were performed with the software GPAW in a non-self consistent way based on underlying selfconsistent GGA (revPBE) calculations.The calculations performed in this thesis indicate that it is important to use a spin-polarised description of the physics to get accurate results for hydrogen adsorption on a graphitic surface.
- PostQuantum state tomography of 1D resonance fluorescence(2017) Strandberg, Ingrid; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap; Chalmers University of Technology / Department of Microtechnology and NanoscienceTomography is the name under which all state reconstruction techniques are denoted, one of the most recognized examples being medical tomography. Quantum state tomography is a procedure to determine the quantum state of a physical system. By performing homodyne measurements on resonance fluorescence from an artificial atom coupled to a one-dimensional transmission line, its quantum state can be reconstructed. Resonance fluorescence is one of the simplest setups that results in non-classical states of light. If these states are non-classical in the sense that they have a negative Wigner function, they can be used as a computational resource for quantum computing. There are many different approaches to quantum computing. Some, like gate based quantum computing using discrete variables like qubits, have been extensively researched, both theoretically and experimentally. There exists and alternative approach: continuous variable quantum computing. The continuous variables we will be concerned with are the components of the electromagnetic field that constitute the resonance fluorescence. There are different parameters that affect the nature of the resonance fluorescence, for example, the number of transmission lines the atom is coupled to, or the strength of the driving field. In this work, we develop the tools necessary to numerically simulate homodyne detection of resonance fluorescence for different sets of parameters, and reconstruct the quantum state as well as calculating the Wigner negativity.