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Articles 1 - 15 of 15
Full-Text Articles in Physics
Second-Order Weak Lensing From Modified Gravity, R. Ali Vanderveld, Robert R. Caldwell, Jason Rhodes
Second-Order Weak Lensing From Modified Gravity, R. Ali Vanderveld, Robert R. Caldwell, Jason Rhodes
Dartmouth Scholarship
We explore the sensitivity of weak gravitational lensing to second-order corrections to the spacetime metric within a cosmological adaptation of the parametrized post-Newtonian framework. Whereas one might expect nonlinearities of the gravitational field to introduce non-Gaussianity into the statistics of the lensing convergence field, we show that such corrections are actually always small within a broad class of scalar-tensor theories of gravity. We show this by first computing the weak lensing convergence within our parametrized framework to second order in the gravitational potential, and then computing the relevant post-Newtonian parameters for scalar-tensor gravity theories. In doing so we show that …
Experimental Characterization Of Coherent Magnetization Transport In A One-Dimensional Spin System, Chandrasekhar Ramanathan, Paola Cappellaro, Lorenza Viola, David G. Cory
Experimental Characterization Of Coherent Magnetization Transport In A One-Dimensional Spin System, Chandrasekhar Ramanathan, Paola Cappellaro, Lorenza Viola, David G. Cory
Dartmouth Scholarship
We experimentally characterize the non-equilibrium, room-temperature magnetization dynamics of a spin chain evolving under an effective double-quantum (DQ) Hamiltonian. We show that the Liouville space operators corresponding to the magnetization and the two-spin correlations evolve 90 degrees out of phase with each other, and drive the transport dynamics. For a nearest-neighbor-coupled N-spin chain, the dynamics are found to be restricted to a Liouville operator space whose dimension scales only as N2, leading to a slow growth of multi-spin correlations. Even though long-range couplings are present in the real system, we find excellent agreement between the analytical predictions …
Approach To Accurately Measuring The Speed Of Optical Precursors, Chuan-Feng Li, Zong-Quan Zhou, Heejeong Jeong, Guang-Can Guo
Approach To Accurately Measuring The Speed Of Optical Precursors, Chuan-Feng Li, Zong-Quan Zhou, Heejeong Jeong, Guang-Can Guo
Dartmouth Scholarship
Precursors can serve as a bound on the speed of information with dispersive medium. We propose a method to identify the speed of optical wavefronts using polarization-based interference in a solid-state device, which can bound the accuracy of the speed of wavefronts to less than 10−4 with conventional experimental conditions. Our proposal may have important implications for optical communications and fast information processing.
A Model Of So-Called "Zebra" Emissions In Solar Flare Radio Burst Continua, R. A. Treumann, R. Nakamura, W. Baumjohann
A Model Of So-Called "Zebra" Emissions In Solar Flare Radio Burst Continua, R. A. Treumann, R. Nakamura, W. Baumjohann
Dartmouth Scholarship
A simple mechanism for the generation of elec- tromagnetic “Zebra” pattern emissions is proposed. “Zebra” bursts are regularly spaced narrow-band radio emissions on the otherwise broadband radio continuum emitted by the ac- tive solar corona. The mechanism is based on the generation of an ion-ring distribution in a magnetic mirror geometry in the presence of a properly directed field-aligned electric po- tential field. Such ion-rings or ion-conics are well known from magnetospheric observations. Under coronal condi- tions they may become weakly relativistic. In this case the ion-cyclotron maser generates a number of electromagnetic ion-cyclotron harmonics which modulate the electron maser …
Reducing Sequencing Complexity In Dynamical Quantum Error Suppression By Walsh Modulation, David Hayes, Kaveh Khodjasteh, Lorenza Viola, Michael J. Biercuk
Reducing Sequencing Complexity In Dynamical Quantum Error Suppression By Walsh Modulation, David Hayes, Kaveh Khodjasteh, Lorenza Viola, Michael J. Biercuk
Dartmouth Scholarship
We study dynamical error suppression from the perspective of reducing sequencing complexity, with an eye toward facilitating the development of efficient semiautonomous quantum-coherent systems. To this end, we focus on digital sequences where all interpulse time periods are integer multiples of a minimum clock period and compatibility with digital classical control circuitry is intrinsic. We use so-called Walsh functions as a unifying mathematical framework; the Walsh functions are an orthonormal set of basis functions which may be associated directly with the control propagator for a digital modulation scheme. Using this insight, we characterize the suite of resulting Walsh dynamical decoupling …
Pointer States Via Engineered Dissipation, Kaveh Khodjasteh, Viatcheslav V. V. Dobrovitski, Lorenza Viola
Pointer States Via Engineered Dissipation, Kaveh Khodjasteh, Viatcheslav V. V. Dobrovitski, Lorenza Viola
Dartmouth Scholarship
Pointer states are long-lasting high-fidelity states in open quantum systems. We show how any pure state in a non-Markovian open quantum system can be made to behave as a pointer state by suitably engineering the coupling to the environment via open-loop periodic control. Engineered pointer states are constructed as approximate fixed points of the controlled open-system dynamics, in such a way that they are guaranteed to survive over a long time with a fidelity determined by the relative precision with which the dynamics is engineered. We provide quantitative minimum-fidelity bounds by identifying symmetry and ergodicity conditions that the decoherence-inducing perturbation …
Decay Of Nuclear Hyperpolarization In Silicon Microparticles, M. Lee, M. C. Cassidy, C. Ramanathan, C. M. Marcus
Decay Of Nuclear Hyperpolarization In Silicon Microparticles, M. Lee, M. C. Cassidy, C. Ramanathan, C. M. Marcus
Dartmouth Scholarship
We investigate the low-field relaxation of nuclear hyperpolarization in undoped and highly doped silicon microparticles at room temperature following removal from high field. For nominally undoped particles, two relaxation time scales are identified for ambient fields above 0.2 mT. The slower, T1,s, is roughly independent of ambient field; the faster, T1,f, decreases with increasing ambient field. A model in which nuclear spin relaxation occurs at the particle surface via a two-electron mechanism is shown to be in good agreement with the experimental data, particularly the field independence of T1,s. For boron-doped particles, a single relaxation time scale is observed. This …
Relativistic Transformation Of Phase-Space Distributions, R A. Treumann, R Nakamura, W Baumjohann
Relativistic Transformation Of Phase-Space Distributions, R A. Treumann, R Nakamura, W Baumjohann
Dartmouth Scholarship
We investigate the transformation of the distri- bution function in the relativistic case, a problem of interest in plasma when particles with high (relativistic) velocities come into play as for instance in radiation belt physics, in the electron-cyclotron maser radiation theory, in the vicin- ity of high-Mach number shocks where particles are acceler- ated to high speeds, and generally in solar and astrophysical plasmas. We show that the phase-space volume element is a Lorentz constant and construct the general particle distri- bution function from first principles. Application to thermal equilibrium lets us derive a modified version of the isotropic relativisticthermaldistribution,themodifiedJu …
The Role Of The Bow Shock In Solar Wind-Magnetosphere Coupling, R E. Lopez, V G. Merkin, J G. Lyon
The Role Of The Bow Shock In Solar Wind-Magnetosphere Coupling, R E. Lopez, V G. Merkin, J G. Lyon
Dartmouth Scholarship
No abstract provided.
Exact Solutions For Social And Biological Contagion Models On Mixed Directed And Undirected, Degree-Correlated Random Networks, Joshua L. Payne, Kameron Decker Harris, Peter Sheridan Dodds
Exact Solutions For Social And Biological Contagion Models On Mixed Directed And Undirected, Degree-Correlated Random Networks, Joshua L. Payne, Kameron Decker Harris, Peter Sheridan Dodds
Dartmouth Scholarship
We derive analytic expressions for the possibility, probability, and expected size of global spread- ing events starting from a single infected seed for a broad collection of contagion processes acting on random networks with both directed and undirected edges and arbitrary degree-degree correla- tions. Our work extends previous theoretical developments for the undirected case, and we provide numerical support for our findings by investigating an example class of networks for which we are able to obtain closed-form expressions.
Turbulence And Bias-Induced Flows In Simple Magnetized Toroidal Plasmas, B. Li, B. N. Rogers, P. Ricci, K. W. Gentle
Turbulence And Bias-Induced Flows In Simple Magnetized Toroidal Plasmas, B. Li, B. N. Rogers, P. Ricci, K. W. Gentle
Dartmouth Scholarship
Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three- dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows. These bias-induced vertical flows located in the gradient region appear to reduce the radial extent of turbulent structures, and thereby lower the radial plasma transport on the low field side.
Direct, Physically-Motivated Derivation Of The Contagion Condition For Spreading Processes On Generalized Random Networks, Peter Sheridan Dodds, Kameron Decker Harris, Joshua L. Payne
Direct, Physically-Motivated Derivation Of The Contagion Condition For Spreading Processes On Generalized Random Networks, Peter Sheridan Dodds, Kameron Decker Harris, Joshua L. Payne
Dartmouth Scholarship
For a broad range of single-seed contagion processes acting on generalized random networks, we derive a unifying analytic expression for the possibility of global spreading events in a straightforward, physically intuitive fashion. Our reasoning lays bare a direct mechanical understanding of an archetypal spreading phenomena that is not evident in circuitous extant mathematical approaches.
Entanglement Patterns In Mutually Unbiased Basis Sets, Jay Lawrence
Entanglement Patterns In Mutually Unbiased Basis Sets, Jay Lawrence
Dartmouth Scholarship
A few simply-stated rules govern the entanglement patterns that can occur in mutually unbiased basis sets (MUBs), and constrain the combinations of such patterns that can coexist (ie , the stoichiometry) in full complements of (pN + 1) MUBs. We consider Hilbert spaces of prime power dimension (as realized by systems of N prime-state particles, or qupits), where full complements are known to exist, and we assume only that MUBs are eigenbases of generalized Pauli operators, without using a particular construction. The general rules include the following: 1) In any MUB, a particular qupit appears either in a pure …
Dynamical Critical Scaling And Effective Thermalization In Quantum Quenches: Role Of The Initial State, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Dynamical Critical Scaling And Effective Thermalization In Quantum Quenches: Role Of The Initial State, Shusa Deng, Gerardo Ortiz, Lorenza Viola
Dartmouth Scholarship
We explore the robustness of universal dynamical scaling behavior in a quantum system near criticality with respect to initialization in a large class of states with finite energy. By focusing on a homogeneous XY quantum spin chain in a transverse field, we characterize the nonequilibrium response under adiabatic and sudden quench processes originating from a pure as well as a mixed excited initial state, and involving either a regular quantum critical or a multicritical point. We find that the critical exponents of the ground-state quantum phase transition can be encoded in the dynamical scaling exponents despite the finite energy of …
Coherent-State Transfer Via Highly Mixed Quantum Spin Chains, Paola Cappellaro, Lorenza Viola, Chandrasekhar Ramanathan
Coherent-State Transfer Via Highly Mixed Quantum Spin Chains, Paola Cappellaro, Lorenza Viola, Chandrasekhar Ramanathan
Dartmouth Scholarship
Spin chains have been proposed as quantum wires in many quantum-information processing architectures. Coherent transmission of quantum information in spin chains over short distances is enabled by their internal dynamics, which drives the transport of single-spin excitations in perfectly polarized chains. Given the practical challenge of preparing the chain in a pure state, we propose to use a chain that is initially in the maximally mixed state. We compare the transport properties of pure and mixed-state chains and find similarities that enable the experimental study of pure-state transfer via mixed-state chains. We also demonstrate protocols for the perfect transfer of …