3,482 research outputs found
Non-equilibrium dynamics of bosonic atoms in optical lattices: Decoherence of many-body states due to spontaneous emission
We analyze in detail the heating of bosonic atoms in an optical lattice due
to incoherent scattering of light from the lasers forming the lattice. Because
atoms scattered into higher bands do not thermalize on the timescale of typical
experiments, this process cannot be described by the total energy increase in
the system alone (which is determined by single-particle effects). The heating
instead involves an important interplay between the atomic physics of the
heating process and the many-body physics of the state. We characterize the
effects on many-body states for various system parameters, where we observe
important differences in the heating for strongly and weakly interacting
regimes, as well as a strong dependence on the sign of the laser detuning from
the excited atomic state. We compute heating rates and changes to
characteristic correlation functions based both on perturbation theory
calculations, and a time-dependent calculation of the dissipative many-body
dynamics. The latter is made possible for 1D systems by combining
time-dependent density matrix renormalization group (t-DMRG) methods with
quantum trajectory techniques.Comment: 17 pages, 14 figure
A fault-tolerant clock
Computers must operate correctly even though one or more of components have failed. Electronic clock has been designed to be insensitive to occurrence of faults; it is substantial advance over any known clock
Measuring entanglement growth in quench dynamics of bosons in an optical lattice
We discuss a scheme to measure the many-body entanglement growth during
quench dynamics with bosonic atoms in optical lattices. By making use of a 1D
or 2D setup in which two copies of the same state are prepared, we show how
arbitrary order Renyi entropies can be extracted using tunnel-coupling between
the copies and measurement of the parity of on-site occupation numbers, as has
been performed in recent experiments. We illustrate these ideas for a
Superfluid-Mott insulator quench in the Bose-Hubbard model, and also for
hard-core bosons, and show that the scheme is robust against imperfections in
the measurements.Comment: 4+ pages plus supplementary materia
Defect-Suppressed Atomic Crystals in an Optical Lattice
We present a coherent filtering scheme which dramatically reduces the site
occupation number defects for atoms in an optical lattice, by transferring a
chosen number of atoms to a different internal state via adiabatic passage.
With the addition of superlattices it is possible to engineer states with a
specific number of atoms per site (atomic crystals), which are required for
quantum computation and the realisation of models from condensed matter
physics, including doping and spatial patterns. The same techniques can be used
to measure two-body spatial correlation functions. We illustrate these ideas
with a scheme to study the creation of a BCS state with a chosen filling factor
from a degenerate Fermi gas in an optical lattice.Comment: 4 Pages, 5 Figures, REVTex
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
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
Photo-induced Tomonaga-Luttinger-like liquid in a Mott insulator
Photo-induced metallic states in a Mott insulator are studied for the
half-filled, one-dimensional Hubbard model with the time-dependent density
matrix renormalization group. An irradiation of strong AC field is found to
create a linear dispersion in the optical spectrum (current-current
correlation) in the nonequilibrium steady state reminiscent of the
Tomonaga-Luttinger liquid for the doped Mott insulator in equilibrium. The spin
spectrum in nonequilibrium retains the des Cloizeaux-Pearson mode with the spin
velocity differing from the charge velocity. The mechanism of the
photocarrier-doping, along with the renormalization in the charge velocity, is
analyzed in terms of an effective Dirac model.Comment: 5 pages, 5 figure
Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part II: Application to the Many-Body Problem
We analyze the ground state phase diagram of attractive lattice bosons, which
are stabilized by a three-body onsite hardcore constraint. A salient feature of
this model is an Ising type transition from a conventional atomic superfluid to
a dimer superfluid with vanishing atomic condensate. The study builds on an
exact mapping of the constrained model to a theory of coupled bosons with
polynomial interactions, proposed in a related paper [11]. In this framework,
we focus by analytical means on aspects of the phase diagram which are
intimately connected to interactions, and are thus not accessible in a mean
field plus spin wave approach. First, we determine shifts in the mean field
phase border, which are most pronounced in the low density regime. Second, the
investigation of the strong coupling limit reveals the existence of a new
collective mode, which emerges as a consequence of enhanced symmetries in this
regime. Third, we show that the Ising type phase transition, driven first order
via the competition of long wavelength modes at generic fillings, terminates
into a true Ising quantum critical point in the vicinity of half filling.Comment: 22 pages, 5 figure
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The fast and forceful kicking strike of the secretary bird
The study of animal locomotion has uncovered principles that can be applied to bio-inspired robotics, prosthetics and rehabilitation medicine, while also providing insight into musculoskeletal form and function [1, 2, 3, 4]. In particular, study of extreme behaviors can reveal mechanical constraints and trade-offs that have influenced evolution of limb form and function [1, 2]. Secretary birds (Sagittarius serpentarius; Figure 1A) are large terrestrial birds of prey endemic to sub-Saharan Africa, which feed on snakes, lizards and small mammals [5]. They frequently kick and stamp on the prey’s head until it is killed or incapacitated, particularly when dispatching larger lizards and venomous snakes [5]. The consequences of a missed strike when hunting venomous snakes can be deadly [5], so the kicking strikes of secretary birds require fast yet accurate neural control. Delivery of fast, forceful and accurate foot strikes that are sufficient to stun and kill prey requires precision targeting, demanding a high level of coordination between the visual and neuromuscular systems
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