Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session L7: General Physics II |
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Chair: Bonnie Anderson, Utah Valley Unversity Room: Lory Student Center 308 |
Saturday, October 21, 2017 11:10AM - 11:22AM |
L7.00001: Visualizing Quantum Erasure using a Series of Stern-Gerlach Magnets Richard Barney, Jean-Francois Van Huele In a standard Stern-Gerlach setup, a quantum object, or quanton, with nonzero spin has its position entangled with its spin by an inhomogeneous magnetic field. This entanglement causes the quanton to exhibit full particle behavior, allowing its spin to be measured by observing its position. We examine a modified setup which passes a beam of single quantons through multiple Stern-Gerlach magnets oriented at different angles perpendicular to the beam. This allows for full or partial erasure of each quanton's path information, recovering wave behavior expressed as self-interference. We present an analytic expression for the wavefunction of a quanton as it moves through such an apparatus. We also discuss a method of quantifying the quanton's wave and particle behaviors and show that these values follow a simple duality relation. [Preview Abstract] |
Saturday, October 21, 2017 11:22AM - 11:34AM |
L7.00002: Topological term in the First Law of Thermodynamics Yiheng Xu, Ferdinand Evers, Charles Stafford We consider entropy and persistent currents induced by the Aharonov-Bohm effect in multiply-connected open quantum systems threaded by a magnetic flux at finite temperature. We prove a strong form of the Nernst theorem (third law of thermodynamics) for ``fully open'' quantum systems: the entropy goes strictly to zero as temperature approaches absolute zero. The conventional formula for the heat current is shown to be problematic for persistent currents, implying a divergent entropy current as temperature goes to zero, in contradiction to the third law. The apparent paradox is resolved through the inclusion of a topological work term in the first law corresponding to the ``persistent electrical work'' done in establishing the Aharonov-Bohm flux. [Preview Abstract] |
Saturday, October 21, 2017 11:34AM - 11:46AM |
L7.00003: An illustration of adiabatic quantum computation: solution of the knapsack problem Mark Coffey The knapsack problem is one of the standard and important difficult challenges for computer science, having broad applications in financial transactions and packing and stock-cutting contexts. As an optimization problem, the main idea is to maximize benefit (profit) subject to weight (cost) constraints. Moreover, solutions of this problem may serve as a facilitator for resolving more complicated problems, including scheduling. This presentation reviews this problem, and briefly its applications, before discussing how a version of quantum computing could be implemented for its solution. This alternative methodology of quantum computing uses systems which have been widely used to model magnetic and other phenomena. It is mentioned that a commercial claimed quantum computing architecture for such problems is available. The aspect of easy- versus difficult-problem instances for NP-hard problems such as knapsack and its subproblem subset sum may also be touched upon. [Preview Abstract] |
Saturday, October 21, 2017 11:46AM - 11:58AM |
L7.00004: Decoherence Effects on a Single Anharmonic Oscillator Ty Beus, Manuel Berrondo Anharmonic oscillators are used to convert coherent states to cat states which can be used as qubits, the building blocks for quantum computing. But there has been little study on the dynamics of anharmonic oscillators under the influence of quantum decoherence. In this presentation, we explore the effects of a single oscillator environment on the anharmonic oscillator and suggest a way to decrease decoherence. [Preview Abstract] |
Saturday, October 21, 2017 11:58AM - 12:10PM |
L7.00005: Application of Lenz's Law to Magnetic Levitation Juan Treto, Heinz Nakotte Lenz’s law can be used to achieve magnetic levitation through induced currents. The law states that changing magnetic fields will induce an electric current, or eddy current, in a conductor surface such that it produces an opposing magnetic field.We will explore the constraints for magnetic levitation through the use of eddy currents, induced by a rotating disk of a permanent-magnet assembly. There are no eddy currents when the disk is stationary, but a rotating disk yields formation of two opposing eddy currents over the dimensions of the individual permanent magnets in the assembly. One of the eddy current repels the magnetic field that created it, while the other eddy current generates an opposite magnetic field resisting a change in the magnetic flux. If the rotation frequency of the magnet assembly is comparable to the typical lifetime of the eddy currents, magnetic levitation may be achieved. We will discuss the parameters that need to be considered for use in an actual device. [Preview Abstract] |
Saturday, October 21, 2017 12:10PM - 12:22PM |
L7.00006: Absence of Landau damping in driven three-component Bose--Einstein condensate in optical lattices Gavriil Shchedrin, Daniel Jaschke, Lincoln D. Carr Multicomponent Bose-Einstein condensates (BECs) are a unique form of matter that allow one to explore coherent many-body phenomena in a macroscopic quantum system by manipulating its internal degrees of freedom. The ground state of alkali-based BECs, which includes $^{7}{\rm Li}$, $^{23}{\rm Na}$, and $^{87}{\rm Rb}$, is characterized by the hyperfine spin $F$, that can be best probed in optical lattices, which liberate its $2F+1$ internal components and thus provides a direct access to its internal structure. We explore the quantum many-body physics of a three-component Bose-Einstein condensate in optical lattices driven by laser fields in $V$ and $\Lambda$ configurations. We obtain exact analytical expressions for the energy spectrum and amplitudes of elementary excitations, and discover symmetries among them. We demonstrate that the applied laser fields induce a gap in the otherwise gapless Bogoliubov spectrum. We find that Landau damping of the collective modes above the energy of the gap is carried by laser-induced roton modes and is considerably suppressed compared to the phonon-mediated damping endemic to undriven scalar condensates. [Preview Abstract] |
Saturday, October 21, 2017 12:22PM - 12:34PM |
L7.00007: Ab Initio Simulation of Photoinduced Ring Currents in Benzene Tennesse Joyce, Agnieszka Jaron-Becker A circularly polarized femtosecond laser can induce electronic ring currents within a single molecule on the order of microamps that are expected to persist for as long as nanoseconds. Photoinduced ring currents have not yet been observed experimentally, and most theoretical studies have assumed weak laser intensity—below about $10^{12}$ W/cm$^2$—which limits the strength of the induced current. To accurately model ring currents in benzene generated by high-intensity femtosecond laser pulses, we have used Time-Dependent Density Functional Theory, a direct ab initio method for molecular calculations. Our results indicate that ionization plays a larger role than previously expected at high intensities, because of a Resonance Enhanced Multiphoton Ionization (REMPI) process. [Preview Abstract] |
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