110 research outputs found
Interaction Quench in the Hubbard model
Motivated by recent experiments in ultracold atomic gases that explore the
nonequilibrium dynamics of interacting quantum many-body systems, we
investigate the opposite limit of Landau's Fermi liquid paradigm: We study a
Hubbard model with a sudden interaction quench, that is the interaction is
switched on at time t=0. Using the flow equation method, we are able to study
the real time dynamics for weak interaction U in a systematic expansion and
find three clearly separated time regimes: i) An initial buildup of
correlations where the quasiparticles are formed. ii) An intermediate
quasi-steady regime resembling a zero temperature Fermi liquid with a
nonequilibrium quasiparticle distribution function. iii) The long time limit
described by a quantum Boltzmann equation leading to thermalization with a
temperature T proportional to U.Comment: Final version as publishe
Diagonalization of system plus environment Hamiltonians
A new approach to dissipative quantum systems modelled by a system plus
environment Hamiltonian is presented. Using a continuous sequence of
infinitesimal unitary transformations the small quantum system is decoupled
from its thermodynamically large environment. Dissipation enters through the
observation that system observables generically decay completely into a
different structure when the Hamiltonian is transformed into diagonal form. The
method is particularly suited for studying low-temperature properties. This is
demonstrated explicitly for the super-Ohmic spin-boson model.Comment: 4 pages, Latex, uses Revte
Non-equilibrium steady state in a periodically driven Kondo model
We investigate the Kondo model with time-dependent couplings that are
periodically switched on and off. On the Toulouse line we derive exact
analytical results for the spin dynamics in the steady state that builds up
after an infinite number of switching periods. Remarkably, the algebraic long
time behavior of the spin-spin correlation function remains completely
unaffected by the driving. In the limit of slow driving the dynamics become
equivalent to that of a single interaction quench. In the limit of fast driving
one can show that the steady state cannot be described by some effective
equilibrium Hamiltonian since a naive implementation of the Trotter formula
gives wrong results. As a consequence, the steady state in the limit of fast
switching serves as an example for the emergence of new quantum states not
accessible in equilibrium.Comment: 13 pages, 4 figures; minor changes, version as publishe
Measurement back-action on adiabatic coherent electron transport
We study the back-action of a nearby measurement device on electrons
undergoing coherent transfer via adiabatic passage (CTAP) in a triple-well
system. The measurement is provided by a quantum point contact capacitively
coupled to the middle well, thus acting as a detector sensitive to the charge
configuration of the triple-well system. We account for this continuous
measurement by treating the whole {triple-well + detector} as a closed quantum
system. This leads to a set of coupled differential equations for the density
matrix of the enlarged system which we solve numerically. This approach allows
to study a single realization of the measurement process while keeping track of
the detector output, which is especially relevant for experiments. In
particular, we find the emergence of a new peak in the distribution of
electrons that passed through the point contact. As one increases the coupling
between the middle potential well and the detector, this feature becomes more
prominent and is accompanied by a substantial drop in the fidelity of the CTAP
scheme
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