Bulletin of the American Physical Society
2015 Joint Fall Meeting of the APS and AAPT New England Sections
Friday–Saturday, November 6–7, 2015; Hanover, New Hampshire
Session B2: Contributed Papers in Condensed Matter and Quantum Information |
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Chair: Chandrasekhar Ramanathan, Dartmouth College Room: Wilder Hall 111 |
Saturday, November 7, 2015 8:30AM - 8:50AM |
B2.00001: A local realistic explanation of quantum information systems that use the four Bell states. Jeffrey Boyd Can quantum computers and other information systems (like cryptography) be explained by local realism? The consensus is NO. Thirty years of Bell test experiment proved that the Einstein, Podolsky and Rosen (EPR) picture is wrong. Unknown to most physicists a new form of realism has arisen, drastically different than EPR. The Theory of Elementary Waves (TEW) proposes that two entangled particles are both following the same elementary bi-ray. What is an elementary ray and bi-ray? In TEW waves and particles usually travel in opposite directions. In entanglement experiments the picture is more complex. A bi-ray consists of two coaxial elementary rays, traveling at the speed of light in opposite directions. In all Bell test experiments TEW and QM make the same predictions. There are other types of experiments in which their predictions differ, and experiments so far are consistent with TEW but inconsistent with QM. Such bi-rays can explain all four Bell states on the basis of local realism. The word “nonlocal” needs to be replaced with the term “elementary bi-ray,” which is a more accurate and fertile descriptor of the same phenomena. TEW provides a solid foundation for quantum informational sciences. It involves a profound change of starting assumptions. [Preview Abstract] |
Saturday, November 7, 2015 8:50AM - 9:10AM |
B2.00002: Study of Quantum Dots using the Finite Element Method Adam Whitney, Jay Wang A quantum dot is a finely tunable two-dimensional quantum system, bound within the nanometer range. They can occur in natural lattice structures, but for production they are often fabricated into semiconductors. The finite element method is a numerical technique for approximating solutions to partial differential equations with boundary conditions by connecting the solutions for a finite number of element equations over the domain. The finite element method is commonly used in various branches of science and engineering, but is not yet often used in the study of quantum dots. We will use the finite element method to find solutions to the Schr\"{o}dinger equation for quantum dots with various boundaries. Simple boundaries can be analyzed in a fairly straightforward manner, but more complicated conditions require computation to solve. We will address questions such as the energy levels of quantum dots, their electronic structure, i.e. the shape of the wave functions, and how they depend on the domain of confinement. These results will help lead us to the study of so-called ``designer atoms'' which are expected to exhibit exotic behavior absent from natural atoms. This will be potentially very useful in nanodevices and other applications of nanoscience. [Preview Abstract] |
Saturday, November 7, 2015 9:10AM - 9:30AM |
B2.00003: Observance of Rise and Decay of Photoconductivity in Ag doped Glassy Thin Film Dipti Sharma, Rajendra Shukla, Ashok Kumar In this study, the rise and decay of photoconductivity was observed as a function of exposure time and light intensity for glassy thin films of Se75Te20Ag5. The thin films of Se75Te20Ag5 chalcogenide glassy alloys were made by evaporation method within a vacuum of 10-5 Torr in the department of Physics at HBTI Kanpur, India. The photoconductivity increases initially, attains a maximum, and then decreases with time as exposure time increases from 15 min to 45 min as well as the light intensity increases from 140 lux to 1450 lux. Under the same experimental conditions, the decay of photocurrent shows a negative photoconductivity during the transient process, and then comes back to zero in many days. This anomalous behavior of photoconductivity can be explained in terms of interaction of photo-excited holes and Ag ions1, 2. 1. D. Sharma, R.K. Shukla and A. Kumar, Thin Solid Films 357 (1999) 214-217 2. D. Sharma, R.K. Shukla, A. Singh, A. K. Nagpal and A. Kumar, Adv. Mater. Opt. Electron. 10 (2000) 251-259 Keywords: Rise and Decay, Photoconductivity; Glasses, Thin films, Se75Te20Ag5, Vacuum, Evaporation method. [Preview Abstract] |
Saturday, November 7, 2015 9:30AM - 9:50AM |
B2.00004: Microwave frequency modulation for improving polarization transfer in DNP experiments M. Guy, C. Ramanathan Dynamic nuclear polarization (DNP) is a driven process that transfers the inherently high electron polarization to surrounding nuclear spins via microwave irradiation at or near the electron Larmor frequency. In a typical DNP experiment, the amplitude and frequency of the applied microwaves are constant; however, by adding time dependence in the form of frequency modulation, polarization transfer between the electron and nuclear spins occurs more efficiently. In particular, triangular and sinusoidal frequency modulation of the applied microwaves during a DNP experiment enhances the final nuclear polarization by as much as a factor 3 over monochromatic irradiation. These modulation schemes increase the electron excitation bandwidth, thereby increasing the number of electrons active in the polarization transfer process and improving overall efficiency. In the present study, we compare the nuclear spin polarization after DNP experiments with (1) no modulation of the applied microwaves, (2) triangular and sinusoidal modulation, and (3) modulation schemes derived from the sample's ESR spectrum. We characterize the polarization as a function of the modulation amplitude and frequency for triangular and sinusoidal modulation and compare the optimal results with our ESR-adapted modulation scheme. We show that by using a modulation scheme tailored to the electronic environment of the sample, polarization transfer is improved. [Preview Abstract] |
Saturday, November 7, 2015 9:50AM - 10:10AM |
B2.00005: Probing carrier-pair spin-spin interactions in a conjugated polymer by detuning of electrically detected beating of Rabi oscillations Kipp van Schooten, Douglas Baird, Mark Limes, John Lupton, Christoph Boehme Radical pair reactions can explain phenomena ranging from avian magnetoreception to spin-dependent charge-carrier recombination and transport rates in semiconductor materials. Central to the radical pair model are weakly-coupled electron spin pairs in a matrix with weak spin--orbit interactions. However, while it has been known that the magnetic-dipolar and spin-exchange interaction strengths within these pairs are weak, specific values within their native operating environment (e.g. within organic light emitting diodes) have been experimentally difficult to obtain. To probe intra-pair coupling strengths \textit{in situ }for an organic semiconductor diode under operating conditions, we use electrically detected magnetic resonance to measure the detuning behavior of Rabi nutation frequencies. In the limit of negligible exchange and dipolar coupling, a fundamental Rabi frequency is analytically predicted to be accompanied by a first harmonic frequency. Deviations from this analytical prediction are due to finite values of exchange and dipolar interactions. By comparing these measured deviations with those obtained from an accurate numerical simulation of various combinations of finite coupling, constraints on both the exchange (\textbar J\textbar \textless 30 neV) and dipolar (\textbar D\textbar $=$23.5 neV) coupling energies are formulated. Further, by considering the dipolar portion alone, a mean intercharge separation of 2.1 nm is implied. [Preview Abstract] |
Saturday, November 7, 2015 10:10AM - 10:30AM |
B2.00006: Temperature Dependence of Electron Spin Coherence in 4H-SiC Margaret Morris, John Colton, Jacob Embley, Samuel Carter Silicon carbide is currently being considered as a promising material for the creation of electron spin based qubits to be used in quantum computing. We examine the ability of electrons in Silicon vacancies in 4H-SiC to remain coherent, which will help us learn whether they will be able to store information long enough to be useful in quantum computing applications. Using a spin echo technique, we measure T2 lifetimes in 4H-SiC for temperatures ranging from 8K to room temperature. The Si vacancies were created through proton irradiation in two different concentrations. We have found a significant temperature dependence in both samples with a maximum lifetime of 77.6 microseconds $+$/- 5.9 in the sample with more concentrated Si vacancies. [Preview Abstract] |
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