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- Title
- DECOHERENCE IN SEMICONDUCTOR SOLID-STATE QUANTUM COMPUTERS.
- Creator
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Valente, Diego, Mucciolo, Eduardo, University of Central Florida
- Abstract / Description
-
In this dissertation we discuss decoherence in charge qubits formed by multiple lateral quantum dots in the framework of the spin-boson model and the Born-Markov approximation. We consider the intrinsic decoherence caused by the coupling to bulk phonon modes and electromagnetic environmental fluctuations. In the case of decoherence caused by phonon coupling, two distinct quantum dot configurations are studied and proposed as setups that mitigate its nocive effects : (i) Three quantum dots in...
Show moreIn this dissertation we discuss decoherence in charge qubits formed by multiple lateral quantum dots in the framework of the spin-boson model and the Born-Markov approximation. We consider the intrinsic decoherence caused by the coupling to bulk phonon modes and electromagnetic environmental fluctuations. In the case of decoherence caused by phonon coupling, two distinct quantum dot configurations are studied and proposed as setups that mitigate its nocive effects : (i) Three quantum dots in a ring geometry with one excess electron in total and (ii) arrays of quantum dots where the computational basis states form multipole charge configurations. For the three-dot qubit, we demonstrate the possibility of performing one- and two-qubit operations by solely tuning gate voltages. Compared to a previous proposal involving a linear three-dot spin qubit, the three-dot charge qubit allows for less overhead on two-qubit operations. For small interdot tunnel amplitudes, the three-dot qubits have Q factors much higher than those obtained for double-dot systems. The high-multipole dot configurations also show a substantial decrease in decoherence at low operation frequencies when compared to the double-dot qubit. We also discuss decoherence due to electromagnetic fluctuations in charge qubits formed by two lateral quantum dots. We use effective circuit models to evaluate correlations of voltage fluctuations in the qubit setup. These correlations allows us to estimate energy (T1) and phase (T2) relaxation times of the the qubit system. We also discuss the dependence the quality factor Q shows with respect to parameters of the setup, such as temperature and capacitive coupling between the electrodes.
Show less - Date Issued
- 2009
- Identifier
- CFE0002961, ucf:47959
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002961
- Title
- Internal Degrees of Freedom and Spin Transitions in Single Molecule Magnets.
- Creator
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Atkinson, James, Del Barco, Enrique, Chen, Bo, Mucciolo, Eduardo, Luis, Fernando, University of Central Florida
- Abstract / Description
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This thesis covers a range of work detailing the transitions between spin eigenstates in molecular magnet systems. Broadly speaking, these transitions can be divided into two kinds: Those that involve a the tunneling of spin through a potential barrier to a resonant state on the other side, a phenomenon known as quantum tunneling of magnetization, and those that occur through the absorption or emission of a photon. In this latter case, the energy of the photon must match the difference...
Show moreThis thesis covers a range of work detailing the transitions between spin eigenstates in molecular magnet systems. Broadly speaking, these transitions can be divided into two kinds: Those that involve a the tunneling of spin through a potential barrier to a resonant state on the other side, a phenomenon known as quantum tunneling of magnetization, and those that occur through the absorption or emission of a photon. In this latter case, the energy of the photon must match the difference between two eigenstates with a difference in angular momentum of ?. We will detail research performed on single molecule magnets, a class of systems that has established itself as an exemplar of higher-order spin interaction. Specifically, we will present the results of studies focused on two Manganese based systems, both of which represent good examples of single molecule magnet behavior. By performing magnetization measurements below the temperature threshold where these systems' polarizations become hysteretic, we find that the precise form of the observed resonant tunneling features (which includes evidence for strong interference of geometric phase a.k.a. Berry phase) can be related to the specifics of the intramolecular interaction. We have analyzed our results using the (")giant spin(") model (which approximates the system as a single spin) as well as with a (")multi-spin(") method which considers all interactions between the ions in the molecular core. We will also discuss the results of measurements performed on a crystalline sample under stress (uniaxial pressure). The data has been analyzed in a framework in which a physical distortion is modelled as a modification of the molecular anisotropy, with different directions of applied stress represented as changes to different parameters governing the molecular energy landscape. This analysis includes simulation of the magnetic relaxation through a master equation approach to the spin-phonon interaction.Finally, our discussion will outline efforts toward understanding the coherent behavior of spin systems. The (")weak(") and (")strong(") coupling between a photon and spin represent two regimes of an interaction by which the information within a spin can be accessed and manipulated. We will discuss the challenges involved in exploring these regimes, both from a theoretical and experimental standpoint. The purpose of this experiment dovetails with those outlined above in attempting to form an intimate basis of knowledge describing the universal relationships to spin at the most fundamental level.
Show less - Date Issued
- 2016
- Identifier
- CFE0006524, ucf:51381
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006524
- Title
- Light Matter Interaction in Single Molecule Magnets.
- Creator
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Cebulka, Rebecca, Del Barco, Enrique, Klemm, Richard, Mucciolo, Eduardo, Luis, Fernando, University of Central Florida
- Abstract / Description
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This dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar...
Show moreThis dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar dephasing. The continuing results of this experiment will be to provide a window into fundamental sources of decoherence in single-crystal SMMs in an energy range not thoroughly investigated. We expect that these conditions would allow us to study the quantum dynamics of the spins as governed by the intrinsic molecular magnetic anisotropy, which should give rise to non-well-defined Rabi oscillations of the spin state, including metastable precessional spin states. In the strong coupling regime, high quality factor superconducting CPW resonators have been designed and fabricated to investigate the vacuum Rabi splitting between a photon and the SMM spin. The proposed setup will permit measurements of coherent collective coupling between molecular spins and a low number of photons, ideally down to a single photon. This experiment may ultimately provide the opportunity for reaching the strong coupling regime with a single spin. Finally, this thesis also documents a research study into the impact of service-learning methodology on students' depth of learning and critical thinking skills during a novel nanoscale science and technology course offered in the UCF Physics Dept. The overall learning of students was assessed and results clearly showed improvement in both multiple choice pre/post-tests and critical reflection papers. We associate this improvement at least partially to the service-learning experience.
Show less - Date Issued
- 2019
- Identifier
- CFE0007442, ucf:52728
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007442