Current Search: Leuenberger, Michael (x)
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 Title
 Entanglement and Coherence in Classical and Quantum Optics.
 Creator

Kagalwala, Kumel, Saleh, Bahaa, Abouraddy, Ayman, Christodoulides, Demetrios, Leuenberger, Michael, University of Central Florida
 Abstract / Description

We explore the concepts of coherence and entanglement as they apply to both the classical and quantum natures of light. In the classical domain, we take inspiration from the tools and concepts developed in foundational quantum mechanics and quantum information science to gain a better understanding of classical coherence theory of light with multiple degrees of freedom (DoFs). First, we use polarization and spatial parity DoFs to demonstrate the notion of classical entanglement, and show that...
Show moreWe explore the concepts of coherence and entanglement as they apply to both the classical and quantum natures of light. In the classical domain, we take inspiration from the tools and concepts developed in foundational quantum mechanics and quantum information science to gain a better understanding of classical coherence theory of light with multiple degrees of freedom (DoFs). First, we use polarization and spatial parity DoFs to demonstrate the notion of classical entanglement, and show that Bell's measure can serve as a useful tool in distinguishing between classical optical coherence theory. Second, we establish a methodical yet versatile approach called 'optical coherency matrix tomography' for reconstructing the coherency matrix of an electromagnetic beam with multiple DoFs. This technique exploits the analogy between this problem in classical optics and that of tomographically reconstructing the density matrix associated with multipartite quantum states in quantum information science. Third, we report the first experimental measurements of the 4 x 4 coherency matrix associated with an electromagnetic beam in which polarization and a spatial DoF are relevant, ranging from the traditional twopoint Young's double slit to spatial parity and orbital angular momentum modes. In the quantum domain, we use the modal structure of classical fields to develop qubits and structure Hilbert spaces for use in quantum information processing. Advancing to threequbit logic gates is an important step towards the success of optical schemes for quantum computing. We experimentally implement a variety of two and three qubit, linear and deterministic, singlephoton, controlled, quantum logic gates using polarization and spatial parity qubits. Lastly, we demonstrate the implementation of twoqubit singlephoton logic using polarization and orbital angular momentum qubits.
Show less  Date Issued
 2015
 Identifier
 CFE0006334, ucf:51546
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006334
 Title
 Electronic Transport Investigation of Chemically Derived Reduced Graphene Oxide Sheets.
 Creator

Joung, Daeha, Khondaker, Saiful, Chow, Lee, Leuenberger, Michael, Zhai, Lei, University of Central Florida
 Abstract / Description

Reduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is...
Show moreReduced graphene oxide (RGO) sheet, a chemically functionalized atomically thin carbon sheet, provides a convenient pathway for producing large quantities of graphene via solution processing. The easy processibility of RGO sheet and its composites offer interesting electronic, chemical and mechanical properties that are currently being explored for advanced electronics and energy based materials. However, a clear understanding of electron transport properties of RGO sheet is lacking which is of great significance for determining its potential application. In this dissertation, I demonstrate fabrication of highyield solution based graphene field effects transistor (FET) using AC dielectrophoresis (DEP) and investigate the detailed electronic transport properties of the fabricated devices. The majority of the devices show ambipolar FET properties at room temperature. However, the mobility values are found to be lower than pristine graphene due to a large amount of residual defects in RGO sheets. I calculate the density of these defects by analyzing the low temperature (295 to 77K) charge transport data using space charge limited conduction (SCLC) with exponential trap distribution. At very low temperature (down to 4.2 K), I observe Coulomb blockade (CB) and EfrosShklovskii variable range hopping (ES VRH) conduction in RGO implying that RGO can be considered as a graphene quantum dots (GQD) array, where graphene domains act like QDs while oxidized domains behave like tunnel barriers between QDs. This was further confirmed by studying RGO sheets of varying carbon sp2 fraction from 55 () 80 % and found that both the localization length and CB can be tuned. From the localization length and using confinement effect, we estimate tunable band gap of RGO sheets with varying carbon sp2 fraction. I then studied one dimensional RGO nanoribbon (RGONR) and found ES VRH and CB models are also applicable to the RGONR. However, in contrast to linear behavior of decrease in threshold voltage (Vt) with increasing temperature (T) in the RGO, sub linear dependence of Vt on T was observed in RGONR due to reduced transport pathways. Finally, I demonstrate synthesis and transport studies of RGO/nanoparticles (CdS and CeO2) composite and show that the properties of RGO can be further tuned by attaching the nanoparticles.
Show less  Date Issued
 2012
 Identifier
 CFE0004785, ucf:49743
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0004785
 Title
 Novel properties of ferromagnetic pwave superconductors.
 Creator

Lorscher, Christopher, Klemm, Richard, Leuenberger, Michael, Rahman, Talat, Schoenfeld, Winston, University of Central Florida
 Abstract / Description

This thesis investigates the many extraordinary physical properties of the candidate pwave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for pwave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H  T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various pwave...
Show moreThis thesis investigates the many extraordinary physical properties of the candidate pwave ferromagnetic superconductors UCoGe and URhGe, and proposes theoretical predictions for pwave superconductors yet to be discovered. In particular, we carry out angular dependent quantum field theoretical calculations of the thermodynamic H  T phase diagram known as the upper critical field, or more appropriately for ferromagnetic superconductors the upper critical induction, for various pwave superconducting order parameter symmetries including: The axial AndersonBrinkmanMorel(ABM) state, the chiral ScharnbergKlemm (SK) state, and the completely broken symmetry polar state (CBS), as well as for some other states with partially broken symmetry (PBS) superconducting order parameter symmetries. The most notable contribution of the work presented in this thesis is the application of the KlemmClem transformations to analytically calculate the full angular and temperature dependencies of the upper critical field for orthorhombic materials, which may prove to be useful to experimentalists in identifying these exotic states of matter experimentally. Second, this work formulates a double spinsplit ellipsoidal Fermi surface (FS) model for ferromagnetic superconductors in the normal state, which introduces a field dependence to the effective mass in one crystallographic direction on the dominant Fermi surface and to the chemical potential, and is subsequently applied to the normal state of URhGe to explain theoretically the anomalous specific heat data of Aoki and Flouquet. Extension of this work to understanding the still elusive reentrant highfield superconducting phase of URhGe and the Sshaped upper critical field curve for external magnetic field parallel to the baxis direction inUCoGe is discussed. Third, this work also presents theoretical fits to the upper critical field data of Kittika et al. for Sr2RuO4 using the helical pwave states and including Pauli limiting effects of the three components of the triplet pairspin fixed to the highly conducting layers by strong spinorbit coupling.
Show less  Date Issued
 2014
 Identifier
 CFE0005371, ucf:50451
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005371
 Title
 First Principle Studies of CuCarbon Nanotube Hybrid Structures with Emphasis on the Electronic Structures and the Transport Properties.
 Creator

Yang, Chengyu, Chen, Quanfang, Leuenberger, Michael, Coffey, Kevin, Ishigami, Marsahir, Fang, Jiyu, University of Central Florida
 Abstract / Description

Carbon nanotubes have been regarded as ideal building blocks for nanoelectronics and multifunctional nanocomposites due to their exceptional strength, stiffness, flexibility, as well as their excellent electrical properties. However, carbon nanotube itself has limitations to fulfill the practical application needs: 1) an individual carbon nanotube has a low density of states at the Fermi level, and thus its conductivity is only comparable to moderate metals but lower than that of copper. 2)...
Show moreCarbon nanotubes have been regarded as ideal building blocks for nanoelectronics and multifunctional nanocomposites due to their exceptional strength, stiffness, flexibility, as well as their excellent electrical properties. However, carbon nanotube itself has limitations to fulfill the practical application needs: 1) an individual carbon nanotube has a low density of states at the Fermi level, and thus its conductivity is only comparable to moderate metals but lower than that of copper. 2) Metallic and semiconducting nanotubes are inherently mixed together from the synthesis, and the selection/separation is very difficult with very low efficiency. 3) Carbon nanotubes alone cannot be used in practical application and a bonding material is normally needed as the join material for actual devices. In this work, we fundamentally explored the possibility that metals (Cu, Al) could tailor carbon nanotube's electronic structure and even transit it from semiconducting to metallic, thus skipping the selection between the metallic and the semiconducting CNTs. We also found out a novel way to enhance a semiconducting CNT system's conductance even better than that of a metallic CNT system. All these researches are done under density functional theory (DFT) frame in conjunction with nonequilibrium Green functions (NEGF).At first we studied the adsorbed copper's influence on the electronic properties of CNT (10, 0) and CNT (5, 5). Results indicate that both the Density of States (DOS) and the transmission coefficients of CNT (5,5) /Cu have been increased. For CNT (10,0)/Cu, the band gap has been shrank, which means the improved conducting properties by the incorporation of copper . As a further case, semiconductor SWCNT (10, 0) with more adsorbed copper chains outside has been studied. 1, 4, 5 and 6 Cu chains have been added onto the carbon nanotube (10,0), and the adsorption of 6 Cu chains finally lead to the transform of the system from semiconducting to metallic. Considering the confining effect, the case that Cu filled into CNT (10, 0) is also studied. It is found that the filled copper chains could modify the system to be metallic more efficiently than the adsorbed Cu chain. Similarly, Al adsorbed on CNT (10, 0) is also studied, and it is found that Al has a better efficiency than copper in tuning the semiconducting CNT to metallic. The existing chemical bonds between the CNT and Al atoms may account for this higher efficiency. In addition, the resultant conductivity of the Al/CNT system is better than that of Cu/CNT system. The Cu/CNT (5,5)+Cu/Cu junction, as another realistic device setup, has been studied in terms of the conductance. The results show that the incorporation of Cu would enhance the conductance of the Cu/CNT/Cu system due to the interaction between Cu and the CNT.
Show less  Date Issued
 2013
 Identifier
 CFE0005280, ucf:50561
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005280