106 research outputs found
Reduced-dimension linear transform coding of distributed correlated signals with incomplete observations
We study the problem of optimal reduced-dimension linear transform coding and reconstruction of a signal based on distributed correlated observations of the signal. In the mean square estimation context this involves finding he optimal signal representation based on multiple incomplete or only partial observations that are correlated. In particular this leads to the study of finding the optimal Karhunen-Loeve basis based on the censored observations. The problem has been considered previously by Gestpar, Dragotti and Vitterli in the context of jointly Gaussian random variables based on using conditional covariances. In this paper, we derive the estimation results in the more general setting of second-order random variables with arbitrary distributions, using entirely different techniques based on the idea of innovations. We explicitly solve the single transform coder case, give a characterization of optimality in the multiple distributed transform coders scenario and provide additional insights into the structure of the problm
Quantum state transfer for multi-input linear quantum systems
Effective state transfer is one of the most important problems in quantum
information processing. Typically, a quantum information device is composed of
many subsystems with multi-input ports. In this paper, we develop a general
theory describing the condition for perfect state transfer from the multi-input
ports to the internal system components, for general passive linear quantum
systems. The key notion used is the zero of the transfer function matrix.
Application to entanglement generation and distribution in a quantum network is
also discussed.Comment: 6 pages, 3 figures. A preliminary condensed version of this work will
appear in Proceedings of the 55th IEEE Conference on Decision and Contro
Comparing resolved-sideband cooling and measurement-based feedback cooling on an equal footing: analytical results in the regime of ground-state cooling
We show that in the regime of ground-state cooling, simple expressions can be
derived for the performance of resolved-sideband cooling --- an example of
coherent feedback control --- and optimal linear measurement-based feedback
cooling for a harmonic oscillator. These results are valid to leading order in
the small parameters that define this regime. They provide insight into the
origins of the limitations of coherent and measurement-based feedback for
linear systems, and the relationship between them. These limitations are not
fundamental bounds imposed by quantum mechanics, but are due to the fact that
both cooling methods are restricted to use only a linear interaction with the
resonator. We compare the performance of the two methods on an equal footing
--- that is, for the same interaction strength --- and confirm that coherent
feedback is able to make much better use of the linear interaction than
measurement-based feedback. We find that this performance gap is caused not by
the back-action noise of the measurement but by the projection noise. We also
obtain simple expressions for the maximal cooling that can be obtained by both
methods in this regime, optimized over the interaction strength.Comment: 14 pages, 2 png figures; v2: revised for publicatio
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