Physics Commons^™

Maximally Entangled States Of Four Nnonbinary Particles, Mario Gaeta, Andrei Klimov, Jay Lawrence

Dartmouth Scholarship

Systems of four nonbinary particles, with each particle having d≥3 internal states, exhibit maximally entangled states that are inaccessible to four qubits. This breaks the pattern of two- and three-particle systems, in which the existing graph states are equally accessible to binary and nonbinary systems alike. We compare the entanglement properties of these special states (called P states) with those of the more familiar Greenberger-Horne-Zeilinger (GHZ) and cluster states accessible to qubits. The comparison includes familiar entanglement measures, the “steering” of states by projective measurements, and the probability that two such measurements, chosen at random, leave the remaining particles in …

Robust Fast Direct Integral Equation Solver For Quasi-Periodic Scattering Problems With A Large Number Of Layers, Min Hyung Cho, Alex H. Barnett

Dartmouth Scholarship

We present a new boundary integral formulation for time-harmonic wave diffraction from two-dimensional structures with many layers of arbitrary periodic shape, such as multilayer dielectric gratings in TM polarization. Our scheme is robust at all scattering parameters, unlike the conventional quasi-periodic Green’s function method which fails whenever any of the layers approaches a Wood anomaly. We achieve this by a decomposition into near- and far-field contributions. The former uses the free-space Green’s function in a second-kind integral equation on one period of the material interfaces and their immediate left and right neighbors; the latter uses proxy point sources and small …

Inductive Measurement Of Optically Hyperpolarized Phosphorous Donor Nuclei In An Isotopically Enriched Silicon-28 Crystal, P. Gumann, O. Patange, C. Ramanathan, H. Haas

Dartmouth Scholarship

We experimentally demonstrate the first inductive readout of optically hyperpolarized phosphorus-31 donor nuclear spins in an isotopically enriched silicon-28 crystal. The concentration of phosphorus donors in the crystal was 1.5×1015  cm−3, 3 orders of magnitude lower than has previously been detected via direct inductive detection. The signal-to-noise ratio measured in a single free induction decay from a 1  cm3 sample (≈1015 spins) was 113. By transferring the sample to an X-band ESR spectrometer, we were able to obtain a lower bound for the nuclear spin polarization at 1.7 K of ∼64%. The 31P-T2 measured with a Hahn echo sequence was …

Iterative Solutions To The Steady-State Density Matrix For Optomechanical Systems, P. D. Nation, J. R. Johansson, M. P. Blencowe, A. J. Rimberg

Dartmouth Scholarship

We present a sparse matrix permutation from graph theory that gives stable incomplete Lower- Upper (LU) preconditioners necessary for iterative solutions to the steady state density matrix for quantum optomechanical systems. This reordering is efficient, adding little overhead to the computation, and results in a marked reduction in both memory and runtime requirements compared to other solution methods, with performance gains increasing with system size. Either of these benchmarks can be tuned via the preconditioner accuracy and solution tolerance. This reordering optimizes the condition number of the approximate inverse, and is the only method found to be stable at large …

Information-Entropic Measure Of Energy-Degenerate Kinks In Two-Field Models, R.A.C. Correa, A. De Souza Dutra, M. Gleiser

Dartmouth Scholarship

We investigate the existence and properties of kink-like solitons in a class of models with two interacting scalar fields. In particular, we focus on models that display both double and single-kink solutions, treatable analytically using the Bogomol'nyi–Prasad–Sommerfield bound (BPS). Such models are of interest in applications that include Skyrmions and various superstring-motivated theories. Exploring a region of parameter space where the energy for very different spatially-bound configurations is degenerate, we show that a newly-proposed momentum–space entropic measure called Configurational Entropy (CE) can distinguish between such energy-degenerate spatial profiles. This information-theoretic measure of spatial complexity provides a complementary perspective to situations …

General Transfer-Function Approach To Noise Filtering In Open-Loop Quantum Control, Gerardo A. Paz-Silva, Lorenza Viola

Dartmouth Scholarship

We present a general transfer-function approach to noise filtering in open-loop Hamiltonian engineering protocols for open quantum systems. We show how to identify a computationally tractable set of fundamental filter functions, out of which arbitrary transfer filter functions may be assembled up to arbitrary high order in principle. Besides avoiding the infinite recursive hierarchy of filter functions that arises in general control scenarios, this fundamental filter-functions set suffices to characterize the error suppression capabilities of the control protocol in both the time and frequency domain. We prove that the resulting notion of filtering order reveals conceptually distinct, albeit complementary, …

Robustness Of Composite Pulses To Time-Dependent Control Noise, Chingiz Kabytayev, Todd J. Green, Kaveh Khodjasteh, Michael J. Biercuk, Lorenza Viola, Kenneth R. Brown

Dartmouth Scholarship

We study the performance of composite pulses in the presence of time-varying control noise on a single qubit. These protocols, originally devised only to correct for static, systematic errors, are shown to be robust to time-dependent non-Markovian noise in the control field up to frequencies as high as ∼10% of the Rabi frequency. Our study combines a generalized filter-function approach with asymptotic dc-limit calculations to give a simple analytic framework for error analysis applied to a number of composite-pulse sequences relevant to nuclear magnetic resonance as well as quantum information experiments. Results include examination of recently introduced concatenated composite pulses …

Fundamental Bounds In Measurements For Estimating Quantum States, Hyang-Tag Lim, Young-Sik Ra, Kang-Hee Hong, Seung-Woo Lee, Yoon-Ho Kim

Dartmouth Scholarship

Quantum measurement unavoidably disturbs the state of a quantum system if any information about the system is extracted. Recently, the concept of reversing quantum measurement has been introduced and has attracted much attention. Numerous efforts have thus been devoted to understanding the fundamental relation of the amount of information obtained by measurement to either state disturbance or reversibility. Here, we experimentally prove the trade-off relations in quantum measurement with respect to both state disturbance and reversibility. By demonstrating the quantitative bound of the trade-off relations, we realize an optimal measurement for estimating quantum systems with minimum disturbance and maximum reversibility. …

Signatures Of The Valley Kondo Effect In Si/Sige Quantum Dots, Mingyun Yuan, R. Joynt, Zhen Yang, Chunyang Tang, D. E. Savage, M. G. Lagally, M. A. Eriksson, A. J. Rimberg

Dartmouth Scholarship

We report measurements consistent with the valley Kondo effect in Si/SiGe quantum dots, evidenced by peaks in the conductance versus source-drain voltage that show strong temperature dependence. The Kondo peaks show unusual behavior in a magnetic field that we interpret as arising from the valley degree of freedom. The interplay of valley and Zeeman splittings is suggested by the presence of side peaks, revealing a zero-field valley splitting between 0.28 to 0.34 meV. A zero-bias conductance peak for nonzero magnetic field, a phenomenon consistent with valley nonconservation in tunneling, is observed in two samples.

Quantum Resources For Purification And Cooling: Fundamental Limits And Opportunities, Francesco Ticozzi, Lorenza Viola

Dartmouth Scholarship

Preparing a quantum system in a pure state is ultimately limited by the nature of the system's evolution in the presence of its environment and by the initial state of the environment itself. We show that, when the system and environment are initially uncorrelated and arbitrary joint unitary dynamics is allowed, the system may be purified up to a certain (possibly arbitrarily small) threshold if and only if its environment, either natural or engineered, contains a “virtual subsystem” which has the same dimension and is in a state with the desired purity. Beside providing a unified understanding of quantum purification …

A Cavity-Cooper Pair Transistor Scheme For Investigating Quantum Optomechanics In The Ultra-Strong Coupling Regime, A. J. Rimberg, M. P. Blencowe, A. D. Armour, P. D. Nation

Dartmouth Scholarship

We propose a scheme involving a Cooper pair transistor (CPT) embedded in a superconducting microwave cavity, where the CPT serves as a charge tunable quantum inductor to facilitate ultra-strong coupling between photons in the cavity and a nano- to meso-scale mechanical resonator. The mechanical resonator is capacitively coupled to the CPT, such that mechanical displacements of the resonator cause a shift in the CPT inductance and hence the cavity's resonant frequency. The amplification provided by the CPT is sufficient for the zero point motion of the mechanical resonator alone to cause a significant change in the cavity resonance. Conversely, a …

Exact And Approximate Solutions For The Quantum Minimum-Kullback-Entropy Estimation Problem, Carlo Sparaciari, Stefano Olivares, Francesco Ticozzi, Matteo G. A. Paris

Dartmouth Scholarship

The minimum-Kullback-entropy principle (mKE) is a useful tool to estimate quantum states and operations from incomplete data and prior information. In general, the solution of an mKE problem is analytically challenging and an approximate solution has been proposed and employed in different contexts. Recently, the form and a way to compute the exact solution for finite dimensional systems has been found, and a question naturally arises on whether the approximate solution could be an effective substitute for the exact solution, and in which regimes this substitution can be performed. Here, we provide a systematic comparison between the exact and the …

Majorana Flat Bands In S -Wave Gapless Topological Superconductors, Shusa Deng, Gerardo Ortiz, Amrit Poudel, Lorenza Viola

Dartmouth Scholarship

We demonstrate how the nontrivial interplay between spin-orbit coupling and nodeless s-wave superconductivity can drive a fully gapped two-band topological insulator into a time-reversal invariant gapless topological superconductor supporting symmetry-protected Majorana flat bands. We characterize topological phase diagrams by a Z2×Z2 partial Berry-phase invariant, and show that, despite the trivial crystal geometry, no unique bulk-boundary correspondence exists. We trace this behavior to the anisotropic quasiparticle bulk gap closing, linear vs quadratic, and argue that this provides a unifying principle for gapless topological superconductivity. Experimental implications for tunneling conductance measurements are addressed, relevant for lead chalcogenide materials.

Hamiltonian Quantum Simulation With Bounded-Strength Controls, Adam D. Bookatz, Pawel Wocjan, Lorenza Viola

Dartmouth Scholarship

We propose dynamical control schemes for Hamiltonian simulation in many-body quantum systems that avoid instantaneous control operations and rely solely on realistic bounded-strength control Hamiltonians. Each simulation protocol consists of periodic repetitions of a basic control block, constructed as a modification of an 'Eulerian decoupling cycle,' that would otherwise implement a trivial (zero) target Hamiltonian. For an open quantum system coupled to an uncontrollable environment, our approach may be employed to engineer an effective evolution that simulates a target Hamiltonian on the system while suppressing unwanted decoherence to the leading order, thereby allowing for dynamically corrected simulation. We …

Gravitational Origin Of The Weak Interaction's Chirality, Stephon Alexander, Antonino Marcianò, Lee Smolin

Dartmouth Scholarship

We present a new unification of the electro-weak and gravitational interactions based on the joining the weak SU(2) gauge fields with the left handed part of the space- time connection, into a single gauge field valued in the complexification of the local Lorentz group. Hence, the weak interactions emerge as the right handed chiral half of the space-time connection, which explains the chirality of the weak interaction. This is possible, because, as shown by Plebanski, Ashtekar, and others, the other chiral half of the space-time connection is enough to code the dynamics of the gravitational degrees of freedom. This unification …

Universal Quantum Fluctuations Of A Cavity Mode Driven By A Josephson Junction, A. D. Armour, M. P. Blencowe, E. Brahimi, A. J. Rimberg

Dartmouth Scholarship

We analyze the quantum dynamics of a superconducting cavity coupled to a voltage-biased Josephson junction. The cavity is strongly excited at resonances where the voltage energy lost by a Cooper pair traversing the circuit is a multiple of the cavity photon energy. We find that the resonances are accompanied by substantial squeezing of the quantum fluctuations of the cavity over a broad range of parameters and are able to identify regimes where the fluctuations in the system take on universal values.

Asymmetric Architecture For Heralded Single-Photon Sources, Luca Mazzarella, Francesco Ticozzi, Alexander V. Sergienko, Giuseppe Vallone, Paolo Villoresi

Dartmouth Scholarship

Single-photon sources represent a fundamental building block for optical implementations of quantum information tasks ranging from basic tests of quantum physics to quantum communication and high-resolution quantum measurement. In this paper, in order to compare the effectiveness of different designs, we introduce a single-photon source performance index, based on the maximum probability of generating a single photon that still guarantees a given signal-to-noise ratio. We then investigate the performance of a multiplexed system based on asymmetric configuration of multiple heralded single-photon sources. The performance and scalability comparison with both currently existing multiple-source architectures and faint laser configurations reveals an advantage …

Designing A Practical High-Fidelity Long-Time Quantum Memory, Kaveh Khodjasteh, Jarrah Sastrawan, David Hayes, Todd J. Green, Michael J. Biercuk, Lorenza Viola

Dartmouth Scholarship

Quantum memory is a central component for quantum information processing devices, and will be required to provide high-fidelity storage of arbitrary states, long storage times and small access latencies. Despite growing interest in applying physical-layer error-suppression strategies to boost fidelities, it has not previously been possible to meet such competing demands with a single approach. Here we use an experimentally validated theoretical framework to identify periodic repetition of a high-order dynamical decoupling sequence as a systematic strategy to meet these challenges. We provide analytic bounds—validated by numerical calculations—on the characteristics of the relevant control sequences and show that a ‘stroboscopic …

Discontinuities And Alfvenic Fluctuations In The Solar Wind, G. Paschmann, S. Haaland, B. Sonnerup, T. Knetter

Dartmouth Scholarship

We examine the Alfvenicity of a set of 188 solar wind directional discontinuities (DDs) identified in the Cluster data from 2003 by Knetter (2005), with the objective of separating rotational discontinuities (RDs) from tangential ones (TDs). The DDs occurred over the full range of solar wind velocities and magnetic shear angles. By performing the Walen test in the de Hoffmann–Teller (HT) frame, we show that 77 of the 127 crossings for which a good HT frame was found had plasma flow speeds exceeding 80 % of the Alfven speed at an average angular deviation of 7.7◦; 33 cases had speeds …

Multiband S -Wave Topological Superconductors: Role Of Dimensionality And Magnetic Field Response, Shusa Deng, Gerardo Ortiz, Lorenza Viola

Dartmouth Scholarship

We further investigate a class of time-reversal-invariant two-band s-wave topological superconductors introduced earlier [Deng, Viola, and Ortiz, Phys. Rev. Lett. 108, 036803 (2012)]. Provided that a sign reversal between the two superconducting pairing gaps is realized, the topological phase diagram can be determined exactly (within mean field) in one and two dimensions as well as in three dimensions upon restricting to the excitation spectrum of time-reversal-invariant momentum modes. We show how, in the presence of time-reversal symmetry, Z2 invariants that distinguish between trivial and nontrivial quantum phases can be constructed by considering only one of the Kramers’ sectors …

A Gamos Plug-In For Geant4 Based Monte Carlo Simulation Of Radiation-Induced Light Transport In Biological Media, Adam K. Glaser, Stephen C. Kanick, Rongxiao Zhang, Pedro Arce, Brian W. Pogue

Dartmouth Scholarship

We describe a tissue optics plug-in that interfaces with the GEANT4/GAMOS Monte Carlo (MC) architecture, providing a means of simulating radiation-induced light transport in biological media for the first time. Specifically, we focus on the simulation of light transport due to the Čerenkov effect (light emission from charged particle's traveling faster than the local speed of light in a given medium), a phenomenon which requires accurate modeling of both the high energy particle and subsequent optical photon transport, a dynamic coupled process that is not well-described by any current MC framework. The results of validation simulations show excellent agreement with …

Inflation In (Super-)Renormalizable Gravity, Fabio Briscese, Antonino Marcianò, Leonardo Modesto, Emmanuel N. Saridakis

Dartmouth Scholarship

We investigate a (super-)renormalizable and ghost-free theory of gravity, showing that under a natural (exponential) ansatz of the form factor and a suitable truncation it can give rise to the Starobinsky inflationary theory in cosmological frameworks, and thus offering a theoretical justification of its origin. We study the corresponding inflationary evolution and we examine the generation of curvature perturbations, adapting the f(R)-like equations in a symmetry-reduced FLRW metric. Furthermore, we analyze how the ultraviolet regime of a simply renormalizable and unitary theory of gravity is also compatible with the Starobinsky action, and hence we show that such a theory could …

Effective Field Theory Approach To Gravitationally Induced Decoherence, M. P. Blencowe

Dartmouth Scholarship

Adopting the viewpoint that the standard perturbative quantization of general relativity provides an effective description of quantum gravity that is valid at ordinary energies, we show that gravity as an environment induces the rapid decoherence of stationary matter superposition states when the energy differences in the superposition exceed the Planck energy scale.

Gauge Field Preheating At The End Of Inflation, J. Tate Deskins, John T. Giblin Jr., Robert R. Caldwell

Dartmouth Scholarship

Here we consider the possibility of preheating the Universe via the parametric amplification of a massless, U(1) abelian gauge field. We assume that the gauge field is coupled to the inflaton via a conformal factor with one free parameter. We present the results of high-resolution three-dimensional simulations of this model and show this mechanism efficiently preheats the Universe to a radiation-dominated final state.

Measures Of Centrality Based On The Spectrum Of The Laplacian, Scott D. Pauls, Daniel Remondini

Dartmouth Scholarship

We introduce a family of new centralities, the k-spectral centralities. k-Spectral centrality is a measurement of importance with respect to the deformation of the graph Laplacian associated with the graph. Due to this connection, k-spectral centralities have various interpretations in terms of spectrally determined information.

We explore this centrality in the context of several examples. While for sparse unweighted net- works 1-spectral centrality behaves similarly to other standard centralities, for dense weighted net- works they show different properties. In summary, the k-spectral centralities provide a novel and useful measurement of relevance (for single network elements as well as whole subnetworks) …

Intrinsic Rotation Of Toroidally Confined Magnetohydrodynamics, Jorge A. Morales, Wouter J. T. T. Bos, Kai Schneider, David C. Montgomery

Dartmouth Scholarship

The spatiotemporal self-organization of viscoresistive magnetohydrodynamics in a toroidal geometry is studied. Curl-free toroidal magnetic and electric fields are imposed. It is observed in our simulations that a flow is generated, which evolves from dominantly poloidal to toroidal when the Lundquist numbers are increased. It is shown that this toroidal organization of the flow is consistent with the tendency of the velocity field to align with the magnetic field. Up-down asymmetry of the geometry causes the generation of a nonzero toroidal angular momentum.

Automated Synthesis Of Dynamically Corrected Quantum Gates, Kaveh Khodjasteh, Hendrik Bluhm, Lorenza Viola

Dartmouth Scholarship

Dynamically corrected gates are extended to non-Markovian open quantum systems where limitations on the available controls and/or the presence of control noise make existing analytical approaches unfeasible. A computational framework for the synthesis of dynamically corrected gates is formalized that allows sensitivity against non-Markovian decoherence and control errors to be perturbatively minimized via numerical search, resulting in robust gate implementations. Explicit sequences for achieving universal high-fidelity control in a singlet-triplet spin qubit subject to realistic system and control constraint are provided, which simultaneously cancel to the leading order the dephasing due to non-Markovian nuclear-bath dynamics and voltage noise affecting the …

Electron Loss And Meteoric Dust In The Mesosphere, M. Friedrich, M. Rapp, T. Blix, U. P. Hoppe, K. Torkar, S. Robertson, S. Dickson, Kristina Lynch

Dartmouth Scholarship

No abstract provided.

Nanomechanical Resonator Coupled Linearly Via Its Momentum To A Quantum Point Contact, Latchezar L. Benatov, Miles P. Blencowe

Dartmouth Scholarship

We use a Born-Markov approximated master equation approach to study the symmetrized-in-frequency current noise spectrum and the oscillator steady state of a nanoelectromechanical system where a nanoscale resonator is coupled linearly via its momentum to a quantum point contact (QPC). Our current noise spectra exhibit clear signatures of the quantum correlations between the QPC current and the back-action force on the oscillator at a value of the relative tunneling phase (η=−π/2) where such correlations are expected to be maximized. We also show that the steady state of the oscillator obeys a classical Fokker-Planck equation, but can experience thermomechanical noise squeezing …

Information Content Of Spontaneous Symmetry Breaking, Marcelo Gleiser, Nikitas Stamatopoulos

Dartmouth Scholarship

We propose a measure of order in the context of nonequilibrium field theory and argue that this measure, which we call relative configurational entropy (RCE), may be used to quantify the emergence of coherent low-entropy configurations, such as time-dependent or time-independent topological and nontopological spatially extended structures. As an illustration, we investigate the nonequilibrium dynamics of spontaneous symmetry breaking in three spatial dimensions. In particular, we focus on a model where a real scalar field, prepared initially in a symmetric thermal state, is quenched to a broken-symmetric state. For a certain range of initial temperatures, spatially localized, long-lived structures known …