48,272 research outputs found
Manipulation of the dynamics of many-body systems via quantum control methods
We investigate how dynamical decoupling methods may be used to manipulate the
time evolution of quantum many-body systems. These methods consist of sequences
of external control operations designed to induce a desired dynamics. The
systems considered for the analysis are one-dimensional spin-1/2 models, which,
according to the parameters of the Hamiltonian, may be in the integrable or
non-integrable limits, and in the gapped or gapless phases. We show that an
appropriate control sequence may lead a chaotic chain to evolve as an
integrable chain and a system in the gapless phase to behave as a system in the
gapped phase. A key ingredient for the control schemes developed here is the
possibility to use, in the same sequence, different time intervals between
control operations.Comment: 10 pages, 3 figure
Entropy of isolated quantum systems after a quench
A diagonal entropy, which depends only on the diagonal elements of the
system's density matrix in the energy representation, has been recently
introduced as the proper definition of thermodynamic entropy in
out-of-equilibrium quantum systems. We study this quantity after an interaction
quench in lattice hard-core bosons and spinless fermions, and after a local
chemical potential quench in a system of hard-core bosons in a superlattice
potential. The former systems have a chaotic regime, where the diagonal entropy
becomes equivalent to the equilibrium microcanonical entropy, coinciding with
the onset of thermalization. The latter system is integrable. We show that its
diagonal entropy is additive and different from the entropy of a generalized
Gibbs ensemble, which has been introduced to account for the effects of
conserved quantities at integrability.Comment: 6 pages, 4 figures, as published (updated supplemental material
Influence of chirping the Raman lasers in an atom gravimeter: phase shifts due to the Raman light shift and to the finite speed of light
We present here an analysis of the influence of the frequency dependence of
the Raman laser light shifts on the phase of a Raman-type atom gravimeter.
Frequency chirps are applied to the Raman lasers in order to compensate gravity
and ensure the resonance of the Raman pulses during the interferometer. We show
that the change in the Raman light shift when this chirp is applied only to one
of the two Raman lasers is enough to bias the gravity measurement by a fraction
of Gal (Gal~=~~m/s). We also show that this effect is
not compensated when averaging over the two directions of the Raman wavevector
. This thus constitutes a limit to the rejection efficiency of the
-reversal technique. Our analysis allows us to separate this effect from the
effect of the finite speed of light, which we find in perfect agreement with
expected values. This study highlights the benefit of chirping symmetrically
the two Raman lasers
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