50,911 research outputs found
Randomized Dynamical Decoupling Techniques for Coherent Quantum Control
The need for strategies able to accurately manipulate quantum dynamics is
ubiquitous in quantum control and quantum information processing. We
investigate two scenarios where randomized dynamical decoupling techniques
become more advantageous with respect to standard deterministic methods in
switching off unwanted dynamical evolution in a closed quantum system: when
dealing with decoupling cycles which involve a large number of control actions
and/or when seeking long-time quantum information storage. Highly effective
hybrid decoupling schemes, which combine deterministic and stochastic features
are discussed, as well as the benefits of sequentially implementing a
concatenated method, applied at short times, followed by a hybrid protocol,
employed at longer times. A quantum register consisting of a chain of spin-1/2
particles interacting via the Heisenberg interaction is used as a model for the
analysis throughout.Comment: 7 pages, 2 figures. Replaced with final version. Invited talk
delivered at the XXXVI Winter Colloquium on the Physics of Quantum
Electronics, Snowbird, Jan 2006. To be published in J. Mod. Optic
Stochastic Model in the Kardar-Parisi-Zhang Universality With Minimal Finite Size Effects
We introduce a solid on solid lattice model for growth with conditional
evaporation. A measure of finite size effects is obtained by observing the time
invariance of distribution of local height fluctuations. The model parameters
are chosen so that the change in the distribution in time is minimum.
On a one dimensional substrate the results obtained from the model for the
roughness exponent from three different methods are same as predicted
for the Kardar-Parisi-Zhang (KPZ) equation. One of the unique feature of the
model is that the as obtained from the structure factor for
the one dimensional substrate growth exactly matches with the predicted value
of 0.5 within statistical errors. The model can be defined in any dimensions.
We have obtained results for this model on a 2 and 3 dimensional substrates.Comment: 8 pages, 7 figures, accepted in Phys. Rev.
Antiresonance and interaction-induced localization in spin and qubit chains with defects
We study a spin chain with an anisotropic XXZ coupling in an external field.
Such a chain models several proposed types of a quantum computer. The chain
contains a defect with a different on-site energy. The interaction between
excitations is shown to lead to two-excitation states localized next to the
defect. In a resonant situation scattering of excitations on each other might
cause decay of an excitation localized on the defect. We find that destructive
quantum interference suppresses this decay. Numerical results confirm the
analytical predictions.Comment: Updated versio
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Optimal Trajectories for Near-Earth-Objects Using Solar Electric Propulsion (SEP) and Gravity Assisted Maneuver
The future interplanetary missions will probably use the conventional chemical rockets to leave the sphere of influence of the Earth, and solar electric propulsion (SEP) to accomplish the other maneuvers of the mission. In this work the optimization of interplanetary missions using solar electric propulsion and Gravity Assisted Maneuver to reduce the costs of the mission, is considered. The high specific impulse of electric propulsion makes a Gravity Assisted Maneuver 1 year after departure convenient. Missions for several Near Earth Asteroids will be considered. The analysis suggests criteria for the definition of initial solutions demanded for the process of optimization of trajectories. Trajectories for the asteroid 2002TC70 are analyzed. Direct trajectories, trajectories with 1 gravity assisted from the Earth and with 2 gravity assisted from the Earth and either Mars are present. An indirect optimization method will be used in the simulations
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