3,952 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
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
BRAVO for many-server QED systems with finite buffers
This paper demonstrates the occurrence of the feature called BRAVO (Balancing
Reduces Asymptotic Variance of Output) for the departure process of a
finite-buffer Markovian many-server system in the QED (Quality and
Efficiency-Driven) heavy-traffic regime. The results are based on evaluating
the limit of a formula for the asymptotic variance of death counts in finite
birth--death processes
Alien Registration- Daley, James H. (Augusta, Kennebec County)
https://digitalmaine.com/alien_docs/18319/thumbnail.jp
Bio-inspired swing leg control for spring-mass robots running on ground with unexpected height disturbance
We proposed three swing leg control policies for spring-mass running robots, inspired by experimental data from our recent collaborative work on ground running birds. Previous investigations suggest that animals may prioritize injury avoidance and/or efficiency as their objective function during running rather than maintaining limit-cycle stability. Therefore, in this study we targeted structural capacity (maximum leg force to avoid damage) and efficiency as the main goals for our control policies, since these objective functions are crucial to reduce motor size and structure weight. Each proposed policy controls the leg angle as a function of time during flight phase such that its objective function during the subsequent stance phase is regulated. The three objective functions that are regulated in the control policies are (i) the leg peak force, (ii) the axial impulse, and (iii) the leg actuator work. It should be noted that each control policy regulates one single objective function. Surprisingly, all three swing leg control policies result in nearly identical subsequent stance phase dynamics. This implies that the implementation of any of the proposed control policies would satisfy both goals (damage avoidance and efficiency) at once. Furthermore, all three control policies require a surprisingly simple leg angle adjustment: leg retraction with constant angular acceleration
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