19,908 research outputs found
Research and development activities in unified control-structure modeling and design
Results of work sponsored by JPL and other organizations to develop a unified control/structures modeling and design capability for large space structures is presented. Recent analytical results are presented to demonstrate the significant interdependence between structural and control properties. A new design methodology is suggested in which the structure, material properties, dynamic model and control design are all optimized simultaneously. The development of a methodology for global design optimization is recommended as a long term goal. It is suggested that this methodology should be incorporated into computer aided engineering programs, which eventually will be supplemented by an expert system to aid design optimization. Recommendations are also presented for near term research activities at JPL. The key recommendation is to continue the development of integrated dynamic modeling/control design techniques, with special attention given to the development of structural models specially tailored to support design
Approximate Randomization of Quantum States With Fewer Bits of Key
Randomization of quantum states is the quantum analogue of the classical
one-time pad. We present an improved, efficient construction of an
approximately randomizing map that uses O(d/epsilon^2) Pauli operators to map
any d-dimensional state to a state that is within trace distance epsilon of the
completely mixed state. Our bound is a log d factor smaller than that of
Hayden, Leung, Shor, and Winter (2004), and Ambainis and Smith (2004).
Then, we show that a random sequence of essentially the same number of
unitary operators, chosen from an appropriate set, with high probability form
an approximately randomizing map for d-dimensional states. Finally, we discuss
the optimality of these schemes via connections to different notions of
pseudorandomness, and give a new lower bound for small epsilon.Comment: 18 pages, Quantum Computing Back Action, IIT Kanpur, March 2006,
volume 864 of AIP Conference Proceedings, pages 18--36. Springer, New Yor
Aspects of nonlocality in atom-photon interactions in a cavity
We investigate a Bell-type inequality for probabilities of detected atoms
formulated using atom-photon interactions in a cavity. We consider decoherence
brought about by both atomic decay, as well as cavity photon loss, and study
its quantitative action in diminishing the atom-field and the resultant
atom-atom secondary correlations. We show that the effects of decoherence on
nonlocality can be observed in a controlled manner in actual experiments
involving the micromaser and also the microlaser.Comment: 9 pages, 3 .eps figures, Revtex. Revised version with details of
calculations and more result
The Effect of Landau Level-Mixing on the Effective Interaction between Electrons in the fractional quantum Hall regime
We compute the effect of Landau-level-mixing on the effective two-body and
three-body pseudopotentials for electrons in the lowest and second Landau
levels. We find that the resulting effective three-body interaction is
attractive in the lowest relative angular momentum channel. The renormalization
of the two-body pseudopotentials also shows interesting structure. We comment
on the implications for the fractional quantum Hall state
Recognizing well-parenthesized expressions in the streaming model
Motivated by a concrete problem and with the goal of understanding the sense
in which the complexity of streaming algorithms is related to the complexity of
formal languages, we investigate the problem Dyck(s) of checking matching
parentheses, with different types of parenthesis.
We present a one-pass randomized streaming algorithm for Dyck(2) with space
\Order(\sqrt{n}\log n), time per letter \polylog (n), and one-sided error.
We prove that this one-pass algorithm is optimal, up to a \polylog n factor,
even when two-sided error is allowed. For the lower bound, we prove a direct
sum result on hard instances by following the "information cost" approach, but
with a few twists. Indeed, we play a subtle game between public and private
coins. This mixture between public and private coins results from a balancing
act between the direct sum result and a combinatorial lower bound for the base
case.
Surprisingly, the space requirement shrinks drastically if we have access to
the input stream in reverse. We present a two-pass randomized streaming
algorithm for Dyck(2) with space \Order((\log n)^2), time \polylog (n) and
one-sided error, where the second pass is in the reverse direction. Both
algorithms can be extended to Dyck(s) since this problem is reducible to
Dyck(2) for a suitable notion of reduction in the streaming model.Comment: 20 pages, 5 figure
Multi-channel Kondo Models in non-Abelian Quantum Hall Droplets
We study the coupling between a quantum dot and the edge of a non-Abelian
fractional quantum Hall state which is spatially separated from it by an
integer quantum Hall state. Near a resonance, the physics at energy scales
below the level spacing of the edge states of the dot is governed by a
-channel Kondo model when the quantum Hall state is a Read-Rezayi state at
filling fraction or its particle-hole conjugate at
. The -channel Kondo model is channel isotropic even without
fine tuning in the former state; in the latter, it is generically channel
anisotropic. In the special case of , our results provide a new venue,
realized in a mesoscopic context, to distinguish between the Pfaffian and
anti-Pfaffian states at filling fraction .Comment: 4 pages, 1 figure; references updated, version to appear in PR
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