Recursos de colección

Caltech Authors (171.365 recursos)

Repository of works by Caltech published authors.

Status = Submitted

Mostrando recursos 1 - 20 de 1.319

  1. Evidence for a quantum-spin-Hall phase in graphene decorated with Bi_2Te_3 nanoparticles

    Hatsuda, K.; Mine, H.; Nakamura, T.; Li, J.; Wu, R.; Alicea, J.; Katsumoto, S.; Haruyama, J.
    Realization of the quantum-spin-Hall effect in graphene devices has remained an outstanding challenge dating back to the inception of the field of topological insulators. Graphene's exceptionally weak spin-orbit coupling-stemming from carbon's low mass-poses the primary obstacle. We experimentally and theoretically study artificially enhanced spin-orbit coupling in graphene via random decoration with dilute Bi2Te3 nanoparticles. Remarkably, multi-terminal resistance measurements suggest the presence of helical edge states characteristic of a quantum-spin-Hall phase; those magnetic-field dependence, X-ray photoelectron spectra, scanning tunneling spectroscopy, and first-principles calculations further support this scenario. These observations highlight a pathway to spintronics and quantum-information applications in graphene-based quantum-spin-Hall platforms.

  2. Steady state of interacting Floquet insulators

    Seetharam, Karthik I.; Bardyn, Charles-Edouard; Lindner, Netanel H.; Rudner, Mark S.; Refael, Gil
    Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought after behavior. How to achieve and control a non-trivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically-driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which...

  3. Modeling Position and Momentum in Finite-Dimensional Hilbert Spaces via Generalized Clifford Algebra

    Singh, Ashmeet; Carroll, Sean M.
    The finite entropy of black holes suggests that local regions of spacetime are described by finite-dimensional factors of Hilbert space, in contrast with the infinite-dimensional Hilbert spaces of quantum field theory. With this in mind, we explore how to cast finite-dimensional quantum mechanics in a form that matches naturally onto the smooth case, especially the recovery of conjugate position/momentum variables, in the limit of large Hilbert-space dimension. A natural tool for this task is the generalized Clifford algebra (GCA). Based on an exponential form of Heisenberg's canonical commutation relation, the GCA offers a finite-dimensional generalization of conjugate variables without relying on any a priori structure on Hilbert space. We highlight...

  4. A Proof of Onsager's Conjecture

    Isett, Philip
    For any α < 1/3, we construct weak solutions to the 3D incompressible Euler equations in the class C_tC^α_x that have nonempty, compact support in time on R × T^3 and therefore fail to conserve the total kinetic energy. This result, together with the proof of energy conservation for α > 1/3 due to [Eyink] and [Constantin, E, Titi], solves Onsager's conjecture that the exponent α = 1/3 marks the threshold for conservation of energy for weak solutions in the class L^∞_tC^α_x. The previous best results were solutions in the class C_tC^α_x for α < 1/5, due to the author,...

  5. On the Endpoint Regularity in Onsager's Conjecture

    Isett, Philip
    Onsager's conjecture states that the conservation of energy may fail for 3D incompressible Euler flows with Hölder regularity below 1/3. This conjecture was recently solved by the author, yet the endpoint case remains an interesting open question with further connections to turbulence theory. In this work, we construct energy non-conserving solutions to the 3D incompressible Euler equations with space-time Hölder regularity converging to the critical exponent at small spatial scales and containing the entire range of exponents [0,1/3). Our construction improves the author's previous result towards the endpoint case. To obtain this improvement, we introduce a new method for optimizing...

  6. Nonuniqueness and existence of continuous, globally dissipative Euler flows

    Isett, Philip
    We show that Hölder continuous, globally dissipative incompressible Euler flows (solutions obeying the local energy inequality) are nonunique and contain examples that strictly dissipate energy. The collection of such solutions emanating from a single initial data may have positive Hausdorff dimension in the energy space even if the local energy equality is imposed, and the set of initial data giving rise to such an infinite family of solutions is C^0 dense in the space of continuous, divergence free vector fields on the torus T^3.

  7. Faster Methods for Contracting Infinite 2D Tensor Networks

    Fishman, M. T.; Vanderstraeten, L.; Zauner-Stauber, V.; Haegeman, J.; Verstraete, F.
    We revisit the Corner Transfer Matrix Renormalization Group (CTMRG) method of Nishino and Okunishi for contracting 2-dimensional tensor networks, and demonstrate that its performance can be substantially improved by determining the tensors using an eigenvalue solver as opposed to the power method used in CTMRG. We also generalize the variational uniform Matrix Product State (VUMPS) ansatz for diagonalizing 1D quantum Hamiltonians to the case of 2D transfer matrices, and discuss similarities with the corner methods. These two new algorithms will be crucial in improving the performance of variational Projected Entangled Pair State (PEPS) methods.

  8. From Dynamical Localization to Bunching in interacting Floquet Systems

    Baum, Yuval; van Nieuwenburg, Evert P. L.; Refael, Gil
    We show that a quantum many-body system may be controlled by means of Floquet engineering, i.e., their properties may be controlled and manipulated by employing periodic driving. We present a concrete driving scheme that allows control over the nature of mobile units and the amount of diffusion in generic many-body systems. We demonstrate these ideas for the Fermi-Hubbard model, where the drive renders doubly occupied sites (doublons) the mobile excitations in the system. In particular, we show that the amount of diffusion in the system and the level of fermion-pairing may be controlled and understood solely in terms of the doublon dynamics. We find that under certain circumstances...

  9. High-fidelity control and entanglement of Rydberg atom qubits

    Levine, Harry; Keesling, Alexander; Omran, Ahmed; Bernien, Hannes; Schwartz, Sylvain; Zibrov, Alexander S.; Endres, Manuel; Greiner, Markus; Vuletic, Vladan; Lukin, Mikhail D.
    Individual neutral atoms excited to Rydberg states are a promising platform for quantum simulation and quantum information processing. However, experimental progress to date has been limited by short coherence times and relatively low gate fidelities associated with such Rydberg excitations. We report progress towards high-fidelity quantum control of Rydberg atom qubits. Enabled by a reduction in laser phase noise, our approach yields a significant improvement in coherence properties of individual qubits. We further show that this high-fidelity control extends to the multi-particle case by preparing a two-atom entangled state with a fidelity exceeding 0.97(3), and extending its lifetime with a two-atom dynamical decoupling protocol. These advances open up new prospects...

  10. Locality of Edge States and Entanglement Spectrum from Strong Subadditivity

    Kato, Kohtaro; Brandão, Fernando G. S. L.
    We consider two-dimensional states of matter satisfying an uniform area law for entanglement. We show that the topological entanglement entropy is equal to the minimum relative entropy distance of the edge state of the system to the set of thermal states of local models. The argument is based on strong subadditivity of quantum entropy. For states with zero topological entanglement entropy, in particular, the formula gives locality of the edge states as thermal states of local Hamiltonians. It also implies that the entanglement spectrum of a region is equal to the spectrum of a one-dimensional local thermal state on the boundary of the region. Our result gives a...

  11. De-Sitter Quantum Loops as the origin of Primordial Non-Gaussianities

    An, Haipeng; Wise, Mark B.; Zhang, Zipei
    It was pointed out recently that in some inflationary models quantum loops containing a scalar of mass m that couples to the inflaton can be the dominant source of primordial non-Gaussianities. We explore this phenomenon in the simplest such model focusing on the behavior of the primordial curvature fluctuations for small m/H. Explicit calculations are done for the three and four point curvature fluctuation correlations. Constraints on the parameters of the model from the CMB limits on primordial non-Gaussianity are discussed. The bi-spectrum in the squeezed limit and the tri-spectrum in the compressed limit are examined. The form of the n-point correlations as any partial sum of wave vectors...

  12. Spectral form factors and late time quantum chaos

    Liu, Junyu
    This is a collection of notes that are about spectral form factors of standard ensembles in the random matrix theory, written for the practical usage of current study of late time quantum chaos. More precisely, we consider Gaussian Unitary Ensemble (GUE), Gaussian Orthogonal Ensemble (GOE), Gaussian Symplectic Ensemble (GSE), Wishart-Laguerre Unitary Ensemble (LUE), Wishart-Laguerre Orthogonal Ensemble (LOE), and Wishart-Laguerre Symplectic Ensemble (LSE). These results and their physics applications cover a three-fold classification of late time quantum chaos in terms of spectral form factors.

  13. An efficient streaming algorithm for spectral proper orthogonal decomposition

    Schmidt, Oliver T.
    A streaming algorithm to compute the spectral proper orthogonal decomposition (SPOD) of stationary random processes is presented. As new data becomes available, an incremental update of the truncated eigenbasis of the estimated cross-spectral density (CSD) matrix is performed. The algorithm converges orthogonal sets of SPOD modes at discrete frequencies that are optimally ranked in terms of energy. We define measures of error and convergence, and demonstrate the algorithm's performance on two datasets. The first example is that of a high-fidelity numerical simulation of a turbulent jet, and the second optical flow data obtained from high-speed camera recordings of a stepped...

  14. First Dark Matter Constraints from SuperCDMS Single-Charge Sensitive Detectors

    Agnese, R.; Aralis, T.; Chang, Y.-Y.; Cornell, B.; Golwala, S. R.
    We present the first limits on inelastic electron-scattering dark matter and dark photon absorption using a prototype SuperCDMS detector having a charge resolution of 0.1 electron-hole pairs (CDMS HVeV, a 0.93 gram CDMS HV device). These electron-recoil limits significantly improve experimental constraints on dark matter particles with masses as low as 1 MeV/c^2. We demonstrate a sensitivity to dark photons competitive with other leading approaches but using substantially less exposure (0.49 gram days). These results demonstrate the scientific potential of phonon-mediated semiconductor detectors that are sensitive to single electronic excitations.

  15. Spectral analysis of jet turbulence

    Schmidt, Oliver T.; Towne, Aaron; Rigas, Georgios; Colonius, Tim; Brès, Guillaume A.
    Informed by LES data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic, and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin-Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by...

  16. Reconciling two notions of quantum operator disagreement: Entropic uncertainty relations and information scrambling, united through quasiprobabilities

    Yunger Halpern, Nicole; Bartolotta, Anthony; Pollack, Jason
    How violently do two quantum operators disagree? Different fields of physics feature different measures of incompatibility: (i) In quantum information theory, entropic uncertainty relations constrain measurement outcomes. (ii) In condensed matter and high-energy physics, the out-of-time-ordered correlator (OTOC) signals scrambling, the spread of information through many-body entanglement. We unite these measures, deriving entropic uncertainty relations for scrambling. The entropies are of distributions over weak and strong measurements' possible outcomes. Weakness causes the OTOC quasiprobability (a nonclassical generalization of a probability, in terms of which the OTOC decomposes) to govern terms in the uncertainty bound. Scrambling strengthens the bound, we show, in numerical simulations of a spin chain. Beyond scrambling, we derive...

  17. Young Accreting Compact Objects in M31: The Combined Power of NuSTAR, Chandra, and Hubble

    Lazzarini, M.; Hornschemeier, A. E.; Williams, B. F.; Wik, D.; Vulic, N.; Yukita, M.; Zezas, A.; Lewis, A. R.; Durbin, M.; Ptak, A.; Bodaghee, A.; Lehmer, B. D.; Antoniou, V.; Maccarone, T.
    We present 15 high mass X-ray binary (HMXB) candidates in the disk of M31 for which we are able to infer compact object type, spectral type of the donor star, and age using multiwavelength observations from NuSTAR, Chandra, and the Hubble Space Telescope (HST). The hard X-ray colors and luminosities from NuSTAR permit the tentative classification of accreting X-ray binary systems by compact object type, distinguishing black hole from neutron star systems. We find hard state black holes, pulsars, and non-magnetized neutron stars associated with optical point source counterparts with similar frequency. We also find nine non-magnetized neutron stars coincident with globular clusters and an equal number of pulsars...

  18. A note on the Liouville function in short intervals

    Matomäki, Kaisa; Radziwiłł, Maksym
    In this note we give a short and self-contained proof that, for any δ > 0, ∑_(x≤n≤x+x^δ)λ(n) = o(x^δ) for almost all x ∈ [X,2X]. We also sketch a proof of a generalization of such a result to general real-valued multiplicative functions. Both results are special cases of results in our more involved and lengthy recent pre-print.

  19. Quantum Unique Ergodicity for half-integral weight automorphic forms

    Lester, Stephen; Radziwiłł, Maksym
    We investigate the analogue of the Quantum Unique Ergodicity (QUE) conjecture for half-integral weight automorphic forms. Assuming the Generalized Riemann Hypothesis (GRH) we establish QUE for both half-integral weight holomorphic Hecke cusp forms for Γ_0(4) lying in Kohnen's plus subspace and for half-integral weight Hecke Maaβ cusp forms for Γ_0(4) lying in Kohnen's plus subspace. By combining the former result along with an argument of Rudnick, it follows that under GRH the zeros of these holomorphic Hecke cusp equidistribute with respect to hyperbolic measure on Γ_0(4)∖H as the weight tends to infinity.

  20. Simulating the classical XY model with a laser network

    Tamate, Shuhei; Yamamoto, Yoshihisa; Marandi, Alireza; McMahon, Peter; Utsunomiya, Shoko
    Drawing fair samples from the Boltzmann distribution of a statistical model is a challenging task for modern digital computers. We propose a physical implementation of a Boltzmann sampler for the classical XY model by using a laser network. The XY spins are mapped onto the phases of multiple laser pulses in a fiber ring cavity and the steady-state distribution of phases naturally realizes the Boltzmann distribution of the corresponding XY model. We experimentally implement the laser network by using an actively mode-locked fiber laser with optical delay lines, and demonstrate Boltzmann sampling for a one-dimensional XY ring.

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