20 research outputs found
Thermalization dynamics close to a quantum phase transition
We investigate the dissipative dynamics of a quantum critical system in
contact with a thermal bath. In analogy with the standard protocol employed to
analyze aging, we study the response of a system to a sudden change of the bath
temperature. The specific example of the XY model in a transverse magnetic
field whose spins are locally coupled to a set of bosonic baths is considered.
The peculiar nature of the dynamics is encoded in the correlations developing
out of equilibrium. By means of a kinetic equation we analyze the spin-spin
correlations and block correlations. We identify some universal features in the
out-of-equilibrium dynamics. Two distinct regimes, characterized by different
time and length scales, emerge. During the initial transient the dynamics is
characterized by the same critical exponents as those of the equilibrium
quantum phase transition and resembles the dynamics of thermal phase
transitions. At long times equilibrium is reached through the propagation along
the chain of a thermal front in a manner similar to the classical Glauber
dynamics.Comment: 4 pages, 4 figures; to be published in Phys. Rev. Let
Adiabatic dynamics in open quantum critical many-body systems
The purpose of this work is to understand the effect of an external
environment on the adiabatic dynamics of a quantum critical system. By means of
scaling arguments we derive a general expression for the density of excitations
produced in the quench as a function of its velocity and of the temperature of
the bath. We corroborate the scaling analysis by explicitly solving the case of
a one-dimensional quantum Ising model coupled to an Ohmic bath.Comment: 4 pages, 4 figures; revised version to be published in Phys. Rev.
Let
Adiabatic dynamics of a quantum critical system coupled to an environment: Scaling and kinetic equation approaches
We study the dynamics of open quantum many-body systems driven across a
critical point by quenching an Hamiltonian parameter at a certain velocity.
General scaling laws are derived for the density of excitations and energy
produced during the quench as a function of quench velocity and bath
temperature. The scaling laws and their regimes of validity are verified for
the XY spin chain locally coupled to bosonic baths. A detailed derivation and
analysis of the kinetic equation of the problem is presented.Comment: 15 pages, 13 figure
Biorobotic Investigation on the Muscle Structure of an OctopusTentacle
The present paper aims at understanding the biomechanics of an octopus tentacle as preliminary work for designing and developing a new robotic octopus tentacle. The biomechanical characterization of the biological material has been carried out on samples of Octopus vulgaris tentacles with engineering methods and tools, i.e. by biomechanical measurements of the tentacle elasticity and tension-compression stress/stretch curves. Another part of the activities has been devoted to the study of materials that can reproduce the viscoelastic behavior of the tentacle. The work presented here is part of the ongoing study and analysis on new design principles for actuation, sensing, and manipulation control, for robots with increased performance, in terms of dexterity, control, flexibility, applicability