Entanglement growth in quench dynamics with variable range interactions

Studying entanglement growth in quantum dynamics provides both insight into the underlying microscopic processes and information about the complexity of the quantum states, which is related to the efficiency of simulations on classical computers. Recently, experiments with trapped ions, polar molecules, and Rydberg excitations have provided new opportunities to observe dynamics with long-range interactions. We explore nonequilibrium coherent dynamics after a quantum quench in such systems, identifying qualitatively different behavior as the exponent of algebraically decaying spin-spin interactions in a transverse Ising chain is varied. Computing the build-up of bipartite entanglement as well as mutual information between distant spins, we identify linear growth of entanglement entropy corresponding to propagation of quasiparticles for shorter range interactions, with the maximum rate of growth occurring when the Hamiltonian parameters match those for the quantum phase transition. Counter-intuitively, the growth of bipartite entanglement for long-range interactions is only logarithmic for most regimes, i.e., substantially slower than for shorter range interactions. Experiments with trapped ions allow for the realization of this system with a tunable interaction range, and we show that the different phenomena are robust for finite system sizes and in the presence of noise. These results can act as a direct guide for the generation of large-scale entanglement in such experiments, towards a regime where the entanglement growth can render existing classical simulations inefficient.Comment: 17 pages, 7 figure

Time-dependent currents of 1D bosons in an optical lattice

We analyse the time-dependence of currents in a 1D Bose gas in an optical lattice. For a 1D system, the stability of currents induced by accelerating the lattice exhibits a broad crossover as a function of the magnitude of the acceleration, and the strength of the inter-particle interactions. This differs markedly from mean-field results in higher dimensions. Using the infinite Time Evolving Block Decimation algorithm, we characterise this crossover by making quantitative predictions for the time-dependent behaviour of the currents and their decay rate. We also compute the time-dependence of quasi-condensate fractions which can be measured directly in experiments. We compare our results to calculations based on phase-slip methods, finding agreement with the scaling as the particle density increases, but with significant deviations near unit filling.Comment: 19 pages, 10 figure

Fault-Tolerant Dissipative Preparation of Atomic Quantum Registers with Fermions

We propose a fault tolerant loading scheme to produce an array of fermions in an optical lattice of the high fidelity required for applications in quantum information processing and the modelling of strongly correlated systems. A cold reservoir of Fermions plays a dual role as a source of atoms to be loaded into the lattice via a Raman process and as a heat bath for sympathetic cooling of lattice atoms. Atoms are initially transferred into an excited motional state in each lattice site, and then decay to the motional ground state, creating particle-hole pairs in the reservoir. Atoms transferred into the ground motional level are no longer coupled back to the reservoir, and doubly occupied sites in the motional ground state are prevented by Pauli blocking. This scheme has strong conceptual connections with optical pumping, and can be extended to load high-fidelity patterns of atoms.Comment: 12 pages, 7 figures, RevTex

Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical Lattice

We show how dissipative dynamics can give rise to pairing for two-component fermions on a lattice. In particular, we construct a "parent" Liouvillian operator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is reached for arbitrary initial states in the absence of conservative forces. The system-bath couplings describe single-particle, number conserving and quasi-local processes. The pairing mechanism crucially relies on Fermi statistics. We show how such Liouvillians can be realized via reservoir engineering with cold atoms representing a driven dissipative dynamics.Comment: 5 pages, 3 figures. Replaced with the published versio

The significance of Anomalocaris and other Radiodonta for understanding paleoecology and evolution during the Cambrian explosion

One of the most widespread and diverse animal groups of the Cambrian Explosion is a clade of stem lineage arthropods known as Radiodonta, which lived exclusively in the early Paleozoic. First reported in 1892 with Anomalocaris canadensis, radiodonts are now one of the best known early animal groups with excellent representation in the fossil record, and are ubiquitous components of <jats:italic>Konservat-Lagerstätten</jats:italic> from the Cambrian and the Early Ordovician. These large swimmers were characterised by a segmented body bearing laterally-oriented flaps, and a head with a distinct radial oral cone, a pair of large frontal appendages adapted for different feeding modes, compound eyes on stalks, and prominent head carapaces. Radiodonts inform on the paleoecology of early animal communities and the steps involved in euarthropod evolution. Four families within Radiodonta have been established. The raptorial predator families Anomalocarididae and Amplectobeluidae were dominant early in the evolutionary history of Radiodonta, but were later overtaken by the mega-diverse and widespread Hurdiidae, which has a more generalised sediment-sifting predatory mode. Suspension feeding, notably in the families Tamisiocarididae and Hurdiidae, also evolved at least twice in the history of the clade. The well-preserved anatomical features of the radiodont body and head have also provided insights into the evolution of characteristic features of Euarthropoda, such as the biramous limbs, compound eyes, and organisation of the head. With 37 species recovered from all major paleocontinents of the Cambrian and Early Ordovician, Radiodonta provides a unique opportunity for revealing evolutionary patterns during the Cambrian Explosion

Dressed, noise- or disorder- resilient optical lattices

External noise is inherent in any quantum system, and can have especially strong effects for systems exhibiting sensitive many-body phenomena. We show how a dressed lattice scheme can provide control over certain types of noise for atomic quantum gases in the lowest band of an optical lattice, removing the effects of lattice amplitude noise to first order for particular choices of the dressing field parameters. We investigate the non-equilibrium many-body dynamics for bosons and fermions induced by noise away from this parameter regime, and also show how the same technique can be used to reduce spatial disorder in projected lattice potentials.Comment: 4+ Pages, 4 Figure

High order non-unitary split-step decomposition of unitary operators

We propose a high order numerical decomposition of exponentials of hermitean operators in terms of a product of exponentials of simple terms, following an idea which has been pioneered by M. Suzuki, however implementing it for complex coefficients. We outline a convenient fourth order formula which can be written compactly for arbitrary number of noncommuting terms in the Hamiltonian and which is superiour to the optimal formula with real coefficients, both in complexity and accuracy. We show asymptotic stability of our method for sufficiently small time step and demonstrate its efficiency and accuracy in different numerical models.Comment: 10 pages, 4 figures (5 eps files) Submitted to J. of Phys. A: Math. Ge

Two-point correlation properties of stochastic "cloud processes''

We study how the two-point density correlation properties of a point particle distribution are modified when each particle is divided, by a stochastic process, into an equal number of identical "daughter" particles. We consider generically that there may be non-trivial correlations in the displacement fields describing the positions of the different daughters of the same "mother" particle, and then treat separately the cases in which there are, or are not, correlations also between the displacements of daughters belonging to different mothers. For both cases exact formulae are derived relating the structure factor (power spectrum) of the daughter distribution to that of the mother. These results can be considered as a generalization of the analogous equations obtained in ref. [1] (cond-mat/0409594) for the case of stochastic displacement fields applied to particle distributions. An application of the present results is that they give explicit algorithms for generating, starting from regular lattice arrays, stochastic particle distributions with an arbitrarily high degree of large-scale uniformity.Comment: 14 pages, 3 figure

Large Area Crop Inventory Experiment (LACIE). Intensive test site assessment report

There are no author-identified significant results in this report

Modulation spectroscopy with ultracold fermions in an optical lattice

We propose an experimental setup of ultracold fermions in an optical lattice to determine the pairing gap in a superfluid state and the spin ordering in a Mott-insulating state. The idea is to apply a periodic modulation of the lattice potential and to use the thereby induced double occupancy to probe the system. We show by full time-dependent calculation using the adaptive time dependent density-matrix renormalization group method that the position of the peak in the spectrum of the induced double occupancy gives the pairing energy in a superfluid and the interaction energy in a Mott-insulator, respectively. In the Mott-insulator we relate the spectral weight of the peak to the spin ordering at finite temperature using perturbative calculations