Search

We study the non-equilibrium dynamics of a one-dimensional Bose gas with long-range interactions that decay as $(\frac{1}{r^{\alpha}})$ $(0.5 < \alpha <4.0$). We investigate the system when the interactions are suddenly switched from the Tonks-Girardeau (TG) to the super-Tonks-Girardeau (sTG) limit. We find that relaxation is achieved through a complex intermediate dynamics demonstrated by violent fragmentation and chaotic delocalization. We establish that the sTG gas exhibits classical gaseous characteristics and an asymptotic state associated with unbounded entropy production. The phase diagram shows an exponential boundary between the nonthermal (quantum) gas and the thermal (classical) gas. We show the universality of the dynamics by also presenting results for spinless fermions. Weaker quench protocols give a certain degree of control over the relaxation process and induce some intermediate quasi-prethermal states. Our study showcases the complex relaxation behavior of tunable long-range interacting systems that could be engineered in state-of-the-art experiments, e.g. in trapped ions or Rydberg atoms., Comment: 14 pages, 13 figures

We study the dynamics of dipolar bosons in an external harmonic trap. We monitor the time evolution of the occupation in the natural orbitals and normalized first- and second-order Glauber's correlation functions. We focus in particular on the relaxation dynamics of the Shannon entropy. Comparison with the corresponding results for contact interactions is presented. We observe significant effects coming from the presence of the non-local repulsive part of the interaction. The relaxation process is very fast for dipolar bosons with a clear signature of a truly saturated maximum entropy state. We also discuss the connection between the entropy production and the occurrence of correlations and loss of coherence in the system. We identify the long-time relaxed state as a many-body state retaining only diagonal correlations in the first-order correlation function and building up anti-bunching effect in the second-order correlation function., Comment: Submitted version of the manuscript

The accuracy of the constrained random phase approximation(cRPA) method is examined in multi-orbital Hubbard models containing all possible on-site density-density interactions. Using DMFT, we show that the effective model constructed using cRPA fails to reproduce the spectral properties of the original full model in a wide parameter range. By comparing quantities such as the density of states and quasiparticle residues of the full and the effective models, we show that cRPA systematically overestimates the screening of Hubbard U for DMFT impurity solvers. We instead propose a new method to investigate the screening mechanism in the system using the local polarization, which is highly successful in reproducing spectra and also shows that the true screening is far less than that predicted by RPA. Furthermore, we compare the fully screened interaction $W$ given by RPA and our new method and show that the RPA $W$ is also overscreened and misses the signatures of local screening, which are clearly present in our new method., Comment: 9 figures, 9 pages

We study the information entropy, order, disorder, and complexity for the two-dimensional (2D) rotating and nonrotating Bose-Einstein condensates. The choice of our system is a complete theoretical laboratory where the complexity is controlled by the two-body contact interaction strength and the rotation frequency ($\Omega$) of the harmonic trap. The 2D nonrotating condensate shows the complexity of the category I where the disorder-order transition is triggered by the interaction strength. In the rotating condensates, $\Omega$ is chosen as the disorder parameter when the interaction strength is fixed. With respect to $\Omega$, the complexity shifts between the maximum and minimum confirm the existence of category II complexity in the rotating condensate. Also, We consider the interaction strength as the disorder parameter when $\Omega$ is unchanged and complexity as a function of interaction strength exhibits category III complexity. The present work also includes the calculation of upper bound and lower bound of entropy for 2D quantum systems.

Understanding the relaxation process is the most important unsolved problem in non-equilibrium quantum physics. Current understanding primarily concerns on if and how an isolated quantum many-body system thermalize. However, there is no clear understanding of what conditions and on which time-scale do thermalization occurs. In this article, we simulate the quench dynamics of one-dimensional Bose gas in an optical lattice from an{\it {ab initio}} perspective by solving the time-dependent many-boson Schr\"odinger equation using the multi-configurational time-dependent Hartree method for bosons (MCTDHB). We direct a superfluid (SF) to Mott-insulator (MI) transition by performing two independent quenches: an interaction quench when the interaction strength is changed instantaneously, and a lattice depth quench where the depth of the lattice is altered suddenly. We show that although the Bose-Hubbard model predicts identical physics, the general many-body treatment shows significant differences between the two cases. We observe that lattice depth quench exhibits a large time-scale to reach the MI state and shows an oscillatory phase collapse-revival dynamics and a complete absence of thermalization that reveals through the analysis of the time-evolution of the reduced one-body density matrix, two-body density, and entropy production. In contrast, the interaction quench shows a swift transition to the MI state and shows a clear signature of thermalization for strong quench values. We provide a physical explanation for these differences and prescribe an analytical fitting formula for the time required for thermalization., Comment: 8 pages, 9 Figures

Fermionization is what happens to the state of strongly interacting repulsive bosons interacting with contact interactions in one spatial dimension. Crystallization is what happens for sufficiently strongly interacting repulsive bosons with dipolar interactions in one spatial dimension. Crystallization and fermionization resemble each other: in both cases -- due to their repulsion -- the bosons try to minimize their spatial overlap. We trace these two hallmark phases of strongly correlated one-dimensional bosonic systems by exploring their ground state properties using the one- and two-body density matrix. We solve the $N$-body Schr\"odinger equation accurately and from first principles using the multiconfigurational time-dependent Hartree for bosons (MCTDHB) and for fermions (MCTDHF) methods. Using the one- and two-body density, fermionization can be distinguished from crystallization in position space. For $N$ interacting bosons, a splitting into an $N$-fold pattern in the one-body and two-body density is a unique feature of both, fermionization and crystallization. We demonstrate that the splitting is incomplete for fermionized bosons and restricted by the confinement potential. This incomplete splitting is a consequence of the convergence of the energy in the limit of infinite repulsion and is in agreement with complementary results that we obtain for fermions using MCTDHF. For crystalline bosons, in contrast, the splitting is complete: the interaction energy is capable of overcoming the confinement potential. Our results suggest that the spreading of the density as a function of the dipolar interaction strength diverges as a power law. We describe how to distinguish fermionization from crystallization experimentally from measurements of the one- and two-body density., Comment: 14 Pages, 9 figures, Resubmitted to Scientific Reports

Already a few bosons with contact interparticle interactions in small optical lattices feature a variety of quantum phases: superfluid, Mott-insulator and fermionized Tonks gases can be probed in such systems. To detect these phases -- pivotal for both experiment and theory -- as well as their many-body properties we analyze several distinct measures for the one-body and many-body Shannon information entropies. We exemplify the connection of these entropies with spatial correlations in the many-body state by contrasting them to the Glauber normalized correlation functions. To obtain the ground-state for lattices with commensurate filling (i.e. an integer number of particles per site) for the full range of repulsive interparticle interactions we utilize the multiconfigurational time-dependent Hartree method for bosons (MCTDHB) in order to solve the many-boson Schr\"odinger equation. We demonstrate that all emergent phases -- the superfluid, the Mott insulator, and the fermionized gas can be characterized equivalently by our many-body entropy measures and by Glauber's normalized correlation functions. In contrast to our many-body entropy measures, single-particle entropy cannot capture these transitions., Comment: 11 pages, 7 figures, software available at http://ultracold.org

The progress in the field of neural computation hinges on the use of hardware more efficient than the conventional microprocessors. Recent works have shown that mixed-signal integrated memristive circuits, especially their passive ('0T1R') variety, may increase the neuromorphic network performance dramatically, leaving far behind their digital counterparts. The major obstacle, however, is relatively immature memristor technology so that only limited functionality has been demonstrated to date. Here we experimentally demonstrate operation of one-hidden layer perceptron classifier entirely in the mixed-signal integrated hardware, comprised of two passive 20x20 metal-oxide memristive crossbar arrays, board-integrated with discrete CMOS components. The demonstrated multilayer perceptron network, whose complexity is almost 10x higher as compared to previously reported functional neuromorphic classifiers based on passive memristive circuits, achieves classification fidelity within 3 percent of that obtained in simulations, when using ex-situ training approach. The successful demonstration was facilitated by improvements in fabrication technology of memristors, specifically by lowering variations in their I-V characteristics., Comment: 26 pages, 12 figures

A Fermi liquid model for hadrons has been suggested for the hadrons in medium. The hadrons are supposed to behave like quasi particle as Fermi excitation while in the medium and the effective mass of the hadrons have been estimated using Fermi liquid model. Considering a momentum dependent potential inside the medium to describe the interaction, the effective masses of the hadrons are estimated. The temperature dependence of effective masses has also been studied. The possibility of describing masses of the quarks as Fermi excitation has been investigated. Compressibility, specific heats, density of states in medium has been studied. The potential depth for light and singly heavy baryons in medium has been extracted. The results are found to be very interesting and compared with the other studies available in literature., Comment: 18 pages, 14 figures

We experimentally demonstrate classification of 4x4 binary images into 4 classes, using a 3-layer mixed-signal neuromorphic network ("MLP perceptron"), based on two passive 20x20 memristive crossbar arrays, board-integrated with discrete CMOS components. The network features 10 hidden-layer and 4 output-layer analog CMOS neurons and 428 metal-oxide memristors, i.e. is almost an order of magnitude more complex than any previously reported functional memristor circuit. Moreover, the inference operation of this classifier is performed entirely in the integrated hardware. To deal with larger crossbar arrays, we have developed a semi-automatic approach to their forming and testing, and compared several memristor training schemes for coping with imperfect behavior of these devices, as well as with variability of analog CMOS neurons. The effectiveness of the proposed schemes for defect and variation tolerance was verified experimentally using the implemented network and, additionally, by modeling the operation of a larger network, with 300 hidden-layer neurons, on the MNIST benchmark. Finally, we propose a simple modification of the implemented memristor-based vector-by-matrix multiplier to allow its operation in a wider temperature range., Comment: 4 pages, 13 figures

A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise due to the competition of localized and itinerant electronic degrees of freedom. While the respective limits of well-localized or entirely itinerant ground states are well-understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and non-bonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum-mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium's magnetism, but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials., Comment: 29 pages, 2 figures, 2 tables, supplementary materials

The masses of the recently reported by LHCb two pentaquark charmonium states $P_{c}^{*}(4380)$ and $P_{c}^{*}(4450)$ which are supposed to have the configuration $(uudc\overline{c})$ have been estimated in the framework of the quasiparticle model of diquarks considering $[ud][uc]\overline{c}$ configuration. The masses are reproduced very well which indicates that the description of diquark as quasiparticle is very useful for describing multiquark state and to understand the dynamics of it.

We study the structural and several quantum properties of three-dimensional bosonic cluster interacting through van der Waals potential at large scattering length. We use Faddeev-type decomposition of the many-body wave function which includes all possible two-body correlations. At large scattering length, we observe spatially extended states which exhibit the exponential dependence on the state number. The cluster ground state energy shows universal nature at large negative scattering length. We also find the existence of generalized Tjon lines for $N$- body clusters. Signature of universal behaviour of weakly bound clusters can be observed in experiments of ultracold Bose gases. We also study the spectral statistics of the system. We calculate both the short-range fluctuation and long-range.correlation and observe semi-Poisson distribution which interpolates the Gaussian Orthogonal Ensemble (GOE) and Poisson statistics of random matrix theory. It indicates that the van der Waal cluster near the unitary becomes highly complex and correlated. However additional study of $P(r)$ distribution (without unfolding of energy spectrum) reveals the possibility of chaos for larger cluster., Comment: online published, Phys Lett A 2017

We study the quantum many-body dynamics and the entropy production triggered by an interaction quench in a system of $N=10$ interacting identical bosons in an external one-dimensional harmonic trap. The multiconfigurational time-dependent Hartree method for bosons (MCTDHB) is used for solving the time-dependent Schr\"odinger equation at a high level of accuracy. We consider many-body entropy measures such as the Shannon information entropy, number of principal components, and occupation entropy that are computed from the time-dependent many-body basis set used in MCTDHB. These measures quantify relevant physical features such as irregular or chaotic dynamics, statistical relaxation and thermalization. We monitor the entropy measures as a function of time and assess how they depend on the interaction strength. For larger interaction strength, the many-body information entropy approaches the value predicted for the Gaussian orthogonal ensemble of random matrices and implies statistical relaxation. The basis states of MCTDHB are explicitly time-dependent and optimized by the variational principle in a way that minimizes the number of significantly contributing ones. It is therefore a non-trivial fact that statistical relaxation prevails in MCTDHB computations. Moreover, we demonstrate a fundamental connection between the production of entropy, the build-up of correlations and loss of coherence in the system. Since the coherence and correlations are experimentally accessible, their present connection to many-body entropies can be scrutinized to detect statistical relaxation. Our results are the first ones obtained for thermalization of finite quantum systems using an optimized time-dependent and genuinely many-body basis set., Comment: 28 pages, 7 figures; used software available at http://ultracold.org

We study the ground state and the low-lying excitations of a trapped Bose gas in an isotropic harmonic potential for very small ($\sim 3$) to very large ($\sim 10^7$) particle numbers. We use the correlated two-body basis functions and the shape-dependent van der Waals interaction in our many-body calculations. We present an exhaustive study of the effect of inter-atomic correlations and the accuracy of the mean-field equations considering a wide range of particle numbers. We calculate the ground state energy and the one-body density for different values of the van der Waals parameter $C_{6}$. We compare our results with those of the modified Gross-Pitaevskii results, the correlated Hartree hypernetted-chain equations (which also utilize the two-body correlated basis functions), as well as of the Diffusion Monte Carlo for hard sphere interactions. We observe the effect of the attractive tail of the van der Waals potential in the calculations of the one-body density over the truly repulsive zero-range potential as used in the Gross-Pitaevskii equation and discuss the finite-size effects. We also present the low-lying collective excitations which are well described by a hydrodynamic model in the large particle limit., Comment: Accepted in J Low Temp Phys

Here we first discuss briefly the quantum annealing technique. We then study the quantum annealing of Sherrington-Kirkpatrick spin glass model with the tuning of both transverse and longitudinal fields. Both the fields are time-dependent and vanish adiabatically at the same time, starting from high values. We solve, for rather small systems, the time-dependent Schrodinger equation of the total Hamiltonian by employing a numerical technique. At the end of annealing we obtain the final state having high overlap with the exact ground state(s) of classical spin glass system (obtained independently)., Comment: 6 pages, 2 figures

The nature of the elemental cerium phases, undergoing an isostructural volume collapse transition, cannot be understood using conventional solid state concepts. Using the combination of density functional theory and dynamical mean-field theory, we study the magnetic properties of both the $\alpha$ and the $\gamma$ phases. We compute the magnetic form factor, and show that it is very close to free ion behavior in both the local moment $\gamma$ phase as well as the more itinerant $\alpha$ phase, in agreement with neutron scattering experiments. In sharp contrast, the dynamic local magnetic susceptibility of the two phases is strikingly different. In the $\gamma$ phase, the sharp low energy peak due to local moment formation and consequently low Kondo temperature dominates the spectra. In the $\alpha$ phase two broad peaks can be identified, the first is due to Kondo screening, and the second is due to Hund's coupling. This shows that hybridization plays a central role in the $\alpha-\gamma$ transition in cerium, and that from the point of view of magnetic properties, the $4f$ electrons are strongly correlated in both phases., Comment: 5 pages, 3 figures

A composite Fermion (CF) model of quasi particle has been used to describe a diquark. Considering baryons in quark-diquark configuration,the masses of the heavy light baryons like $\Lambda_{c}^{+}$, $\Sigma_{c}^{+}$, $\Xi_{c}^{0}$, $\Omega_{c}^{0}$ and $\Lambda_{b}^{+}$, $\Sigma_{b}^{+}$, $\Xi_{b}^{0}$, $\Omega_{b}^{-}$ have been computed using this CF model of the diquark. The results are found to be in good agreement with the corresponding experimental findings. It has been suggested that the diquark can be well described in the framework of CF model in a gauge invariant way.

The properties of the nucleons in nuclear medium have been investigated in the context of the flux tube model incorporating strangeness $(s\bar{s})$ contribution to proton structure in conformity with the experimental indication. Proton is described as a pentaquark system with strange quark contribution whereas neutron is described in three quark configuration. The Quasi particle model of diquark is used to describe the structures of the nucleons. Modifications of the properties like swelling, mass, incompressibility, ratio of the structure functions ($\frac{F_{2}^{n}(x)}{F_{2}^{p}(x)}$), Gottfried Sum rule for nucleons in nuclear medium have been studied and significant effects have been observed. It has been suggested that the change of the size degree of freedom of the nucleon in the nuclear medium plays an important role in describing the properties in medium. The results are discussed in detail and compared with existing experimental and theoretical predictions. Some interesting observations are made.

We show that polarons can sustain loop-like configurations in flexible bio-polymers and that the size of the loops depend on both the flexural rigidity of the polymer and the electron-phonon coupling constant. In particular we show that for single stranded DNA (ssDNA) such loops can have as little as 10 base pairs. For polyacetylene the shortest loop must have at least 12 nodes. We also show that these configurations are very stable under thermal fluctuations and can facilitate the formation of hairpin-loops of ssDNA., Comment: 18 pages, 7 figures, and 1 table

The effect of fractal space time of the quantum particles on the variation of the fine structure constant $\alpha$ has been studied. The variation of fine structure constant has been investigated around De Broglie length $\lambda$ and compton length $\lambda_{c}$ and it has been suggested that the variation may be attributed to the dimensional transition of the particle trajectories between these two quantum domains. Considering the Fractal universe with a small inhomogeneity in the mass distribution in the early universe, the variation of the fine structure constant have been investigated between matter and radiation dominated era. The fine structure constant shows a critical behaviour with critical exponent which is fractional and shows a discontinuity. It has been suggested that the variation of the fine structure constant may be attributed to the intrinsic scale dependance of the fundamental constants of nature.

Polarons, introduced by Davydov to explain energy transport in $\alpha$-helices, correspond to electrons localised on a few lattice sites because of their interaction with phonons. While the static polaron field configurations have been extensively studied, their displacement is more difficult to explain. In this paper we show that, when the next to nearest neighbour interactions are included, for physical values of the parameters, polarons can spontaneously move, at T=0, on bent chains that exhibit a positive gradient in their curvature. At room temperature polarons perform a random walk but a curvature gradient can induce a non-zero average speed similar to the one observed at zero temperature. We also show that at zero temperature a polaron bounces on sharply kinked junctions. We interpret these results in light of the energy transport by transmembrane proteins., Comment: 9 pages, 5 figures

The modification of the properties of nucleon in nuclear medium have been investigated in the context of flux tube model. A nucleon has been described as diquark-quark system connected by flux tube and quasi particle diquark model has been used to describe the diquak constituting the nucleon. The modification of incompressiblity, the roper resonance etc in the nuclear medium have been investigated. The results are compared with recent experimental and theoretical predictions.

The properties of the neutrino in the early universe have been investigated incorporating a small inhomogeneity in the mass density of the early universe. Dependence on this factor is found in studying mean free path and mass bound of neutrinos. The oscillations of neutrinos flavours have been studied by assuming a free wave packet to represent the time progression of the neutrino yielding interesting results., Comment: The manuscript consists of 13 pages with no figures