Ballistic spreading of entanglement in a diffusive nonintegrable system

We study the time evolution of the entanglement entropy of a one-dimensional nonintegrable spin chain, starting from random nonentangled initial pure states. We use exact diagonalization of a nonintegrable quantum Ising chain with transverse and longitudinal fields to obtain the exact quantum dynamics. We show that the entanglement entropy increases linearly with time before finite-size saturation begins, demonstrating a ballistic spreading of the entanglement, while the energy transport in the same system is diffusive. Thus we explicitly demonstrate that the spreading of entanglement is much faster than the energy diffusion in this nonintegrable system.Comment: 7 pages, 7 figures. Published version. Supplementary material adde

Superdiffusive nonequilibrium motion of an impurity in a Fermi sea

We treat the nonequilibrium motion of a single impurity atom in a low-temperature single-species Fermi sea, interacting via a contact interaction. In the nonequilibrium regime, the impurity does a superdiffusive geometric random walk where the typical distance traveled grows with time as $\sim t^{d/(d+1)}$ for the $d$-dimensional system with $d\geq 2$. For nonzero temperature $T$, this crosses over to diffusive motion at long times with diffusivity $D\sim T^{-(d-1)/2}$. These results apply also to a nonzero concentration of impurity atoms as long as they remain dilute and nondegenerate.Comment: 5 pages, 1 figure, to appear in Phys. Rev.

Entanglement spreading in a many-body localized system

Motivated by the findings of logarithmic spreading of entanglement in a many-body localized system, we more closely examine the spreading of entanglement in the fully many-body localized phase, where all many-body eigenstates are localized. Performing full diagonalizations of an XXZ spin model with random longitudinal fields, we identify two factors contributing to the spreading rate: the localization length ($\xi$), which depends on the disorder strength, and the final value of entanglement per spin ($s_\infty$), which primarily depends on the initial state. We find that the entanglement entropy grows with time as $\sim \xi \times s_\infty \log t$, providing support for the phenomenology of many-body localized systems recently proposed by Huse and Oganesyan [arXiv:1305.4915v1].Comment: 7 pages, 5 figure

Thermalization of entanglement

We explore the dynamics of the entanglement entropy near equilibrium in highly-entangled pure states of two quantum-chaotic spin chains undergoing unitary time evolution. We examine the relaxation to equilibrium from initial states with either less or more entanglement entropy than the equilibrium value, as well as the dynamics of the spontaneous fluctuations of the entanglement that occur in equilibrium. For the spin chain with a time-independent Hamiltonian and thus an extensive conserved energy, we find slow relaxation of the entanglement entropy near equilibration. Such slow relaxation is absent in a Floquet spin chain with a Hamiltonian that is periodic in time and thus has no local conservation law. Therefore, we argue that slow diffusive energy transport is responsible for the slow relaxation of the entanglement entropy in the Hamiltonian system.Comment: 6 pages, 6 figures; as in journa

Testing whether all eigenstates obey the Eigenstate Thermalization Hypothesis

We ask whether the Eigenstate Thermalization Hypothesis (ETH) is valid in a strong sense: in the limit of an infinite system, {\it every} eigenstate is thermal. We examine expectation values of few-body operators in highly-excited many-body eigenstates and search for `outliers', the eigenstates that deviate the most from ETH. We use exact diagonalization of two one-dimensional nonintegrable models: a quantum Ising chain with transverse and longitudinal fields, and hard-core bosons at half-filling with nearest- and next-nearest-neighbor hopping and interaction. We show that even the most extreme outliers appear to obey ETH as the system size increases, and thus provide numerical evidences that support ETH in this strong sense. Finally, periodically driving the Ising Hamiltonian, we show that the eigenstates of the corresponding Floquet operator obey ETH even more closely. We attribute this better thermalization to removing the constraint of conservation of the total energy.Comment: 9 pages, 6 figures. Updated references and clarified some argument

Heat and spin transport in a cold atomic Fermi gas

Motivated by recent experiments measuring the spin transport in ultracold unitary atomic Fermi gases (Sommer et al., 2011; Sommer et al., 2011), we explore the theory of spin and heat transport in a three-dimensional spin-polarized atomic Fermi gas. We develop estimates of spin and thermal diffusivities and discuss magnetocaloric effects, namely the the spin Seebeck and spin Peltier effects. We estimate these transport coefficients using a Boltzmann kinetic equation in the classical regime and present experimentally accessible signatures of the spin Seebeck effect. We study an exactly solvable model that illustrates the role of momentum-dependent scattering in the magnetocaloric effects.Comment: 18 pages, 6 figures, slight notation changes from previous versio

Interfering directed paths and the sign phase transition

We revisit the question of the "sign phase transition" for interfering directed paths with real amplitudes in a random medium. The sign of the total amplitude of the paths to a given point may be viewed as an Ising order parameter, so we suggest that a coarse-grained theory for system is a dynamic Ising model coupled to a Kardar-Parisi-Zhang (KPZ) model. It appears that when the KPZ model is in its strong-coupling ("pinned") phase, the Ising model does not have a stable ferromagnetic phase, so there is no sign phase transition. We investigate this numerically for the case of {\ss}1+1 dimensions, demonstrating the instability of the Ising ordered phase there.Comment: 4 pages, 4 figure

Analysis of protein complexes through model‐based biclustering of label‐free quantitative AP‐MS data

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102630/1/msb201041.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102630/2/msb201041-sup-0001.pd

Analysis of hidden terminals effect on the performance of vehicular ad-hoc networks

Vehicular ad-hoc networks (VANETs) based on the IEEE 802.11p standard are receiving increasing attention for road safety provisioning. Hidden terminals, however, demonstrate a serious challenge in the performance of VANETs. In this paper, we investigate the effect of hidden terminals on the performance of one hop broadcast communication. The paper formulates an analytical model to analyze the effect of hidden terminals on the performance metrics such as packet reception probability (PRP), packet reception delay (PRD), and packet reception interval (PRI) for the 2-dimensional (2-D) VANET. To verify the accuracy of the proposed model, the analytical model-based results are compared with NS3 simulation results using 2-D highway scenarios. We also compare the analytical results with those from real vehicular network implemented using the commercial vehicle-to-everything (V2X) devices. The analytical results show high correlation with the results of both simulation and real network.This work was supported in part by IITP Grant through the Korean Government, under the development of wide area driving environment awareness and cooperative driving technology which are based on V2X wireless communication under grant R7117-19- 0164 and in part by the Center for Integrated Smart Sensors funded by the Ministry of Science, ICT & Future Planning as Global Frontier Project, South Korea (CISS-2019)