93 research outputs found
Quantum Ratchets for Quantum Communication with Optical Superlattices
We propose to use a quantum ratchet to transport quantum information in a
chain of atoms trapped in an optical superlattice. The quantum ratchet is
created by a continuous modulation of the optical superlattice which is
periodic in time and in space. Though there is zero average force acting on the
atoms, we show that indeed the ratchet effect permits atoms on even and odd
sites to move along opposite directions. By loading the optical lattice with
two-level bosonic atoms, this scheme permits to perfectly transport a qubit or
entangled state imprinted in one or more atoms to any desired position in the
lattice. From the quantum computation point of view, the transport is achieved
by a smooth concatenation of perfect swap gates. We analyze setups with
noninteracting and interacting particles and in the latter case we use the
tools of optimal control to design optimal modulations. We also discuss the
feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure
Theoretical analysis of quantum dynamics in 1D lattices: Wannier-Stark description
This papers presents a formalism describing the dynamics of a quantum
particle in a one-dimensional tilted time-dependent lattice. The description
uses the Wannier-Stark states, which are localized in each site of the lattice
and provides a simple framework leading to fully-analytical developments.
Particular attention is devoted to the case of a time-dependent potential,
which results in a rich variety of quantum coherent dynamics is found.Comment: 8 pages, 6 figures, submitted to PR
Wavepacket reconstruction via local dynamics in a parabolic lattice
We study the dynamics of a wavepacket in a potential formed by the sum of a
periodic lattice and of a parabolic potential. The dynamics of the wavepacket
is essentially a superposition of ``local Bloch oscillations'', whose frequency
is proportional to the local slope of the parabolic potential. We show that the
amplitude and the phase of the Fourier transform of a signal characterizing
this dynamics contains information about the amplitude and the phase of the
wavepacket at a given lattice site. Hence, {\em complete} reconstruction of the
the wavepacket in the real space can be performed from the study of the
dynamics of the system.Comment: 4 pages, 3 figures, RevTex
Investigation on Parameters Affecting the Effectiveness of Photocatalytic Functional Coatings to Degrade NO: TiO 2
This paper deals with the degradation of NO by photocatalytic oxidation using TiO2-based coatings. Tests are conducted at a laboratory scale through an experimental setup inspired from ISO 22197-1 standard. Various parameters are explored to evaluate their influence on photocatalysis efficiency: TiO2 dry matter content applied to the surface, nature of the substrate, and illumination conditions (UV and visible light). This article points out the different behaviors between three kinds of substrates which are common building materials: normalized mortar, denser mortar, and commercial wood. The illumination conditions are of great importance in the photocatalytic process with experiments under UV light showing the best results. However, a significant decrease in NO concentration under visible light is also observed provided that the TiO2 dry matter content on the surface is high enough. The nature of the substrate plays an important role in the photocatalytic activity with rougher substrates being more efficient to degrade NO. However, limiting the roughness of the substrate seems to be of utmost interest to obtain the highest exposed surface area and thus the optimal photocatalytic efficiency. A higher roughness promotes the surface contact between TiO2 and NO but does not necessarily increase the photochemical oxidation
An accelerator mode based technique for studying quantum chaos
We experimentally demonstrate a method for selecting small regions of phase
space for kicked rotor quantum chaos experiments with cold atoms. Our technique
uses quantum accelerator modes to selectively accelerate atomic wavepackets
with localized spatial and momentum distributions. The potential used to create
the accelerator mode and subsequently realize the kicked rotor system is formed
by a set of off-resonant standing wave light pulses. We also propose a method
for testing whether a selected region of phase space exhibits chaotic or
regular behavior using a Ramsey type separated field experiment.Comment: 5 pages, 3 figures, some modest revisions to previous version (esp.
to the figures) to aid clarity; accepted for publication in Physical Review A
(due out on January 1st 2003
Atomic motion in tilted optical lattices
This paper presents a formalism describing the dynamics of a quantum particle
in a one-dimensional, time-dependent, tilted lattice. The formalism uses the
Wannier-Stark states, which are localized in each site of the lattice, and
provides a simple framework allowing fully-analytical developments. Analytic
solutions describing the particle motion are explicit derived, and the
resulting dynamics is studied.Comment: 6 pages, 2 figs, submitted to EPJD, Springer Verlag styl
Dynamical Localization in Quasi-Periodic Driven Systems
We investigate how the time dependence of the Hamiltonian determines the
occurrence of Dynamical Localization (DL) in driven quantum systems with two
incommensurate frequencies. If both frequencies are associated to impulsive
terms, DL is permanently destroyed. In this case, we show that the evolution is
similar to a decoherent case. On the other hand, if both frequencies are
associated to smooth driving functions, DL persists although on a time scale
longer than in the periodic case. When the driving function consists of a
series of pulses of duration , we show that the localization time
increases as as the impulsive limit, , is
approached. In the intermediate case, in which only one of the frequencies is
associated to an impulsive term in the Hamiltonian, a transition from a
localized to a delocalized dynamics takes place at a certain critical value of
the strength parameter. We provide an estimate for this critical value, based
on analytical considerations. We show how, in all cases, the frequency spectrum
of the dynamical response can be used to understand the global features of the
motion. All results are numerically checked.Comment: 7 pages, 5 figures included. In this version is that Subsection III.B
and Appendix A on the quasiperiodic Fermi Accelerator has been replaced by a
reference to published wor
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