Recursos de colección
Caltech Authors (171.365 recursos)
Repository of works by Caltech published authors.
Status = Submitted
Repository of works by Caltech published authors.
Status = Submitted
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.
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...
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...
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,...
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...
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.
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.
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...
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...
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...
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...
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.
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...
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.
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...
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...
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...
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.
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.
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.