2,205 research outputs found
Ground-state Stabilization of Open Quantum Systems by Dissipation
Control by dissipation, or environment engineering, constitutes an important
methodology within quantum coherent control which was proposed to improve the
robustness and scalability of quantum control systems. The system-environment
coupling, often considered to be detrimental to quantum coherence, also
provides the means to steer the system to desired states. This paper aims to
develop the theory for engineering of the dissipation, based on a ground-state
Lyapunov stability analysis of open quantum systems via a Heisenberg-picture
approach. Algebraic conditions concerning the ground-state stability and
scalability of quantum systems are obtained. In particular, Lyapunov stability
conditions expressed as operator inequalities allow a purely algebraic
treatment of the environment engineering problem, which facilitates the
integration of quantum components into a large-scale quantum system and draws
an explicit connection to the classical theory of vector Lyapunov functions and
decomposition-aggregation methods for control of complex systems. The
implications of the results in relation to dissipative quantum computing and
state engineering are also discussed in this paper.Comment: 18 pages, to appear in Automatic
On the generalization of linear least mean squares estimation to quantum systems with non-commutative outputs
The purpose of this paper is to study the problem of generalizing the
Belavkin-Kalman filter to the case where the classical measurement signal is
replaced by a fully quantum non-commutative output signal. We formulate a least
mean squares estimation problem that involves a non-commutative system as the
filter processing the non-commutative output signal. We solve this estimation
problem within the framework of non-commutative probability. Also, we find the
necessary and sufficient conditions which make these non-commutative estimators
physically realizable. These conditions are restrictive in practice.Comment: 31 page
Interpolation Approach to Hamiltonian-varying Quantum Systems and the Adiabatic Theorem
Quantum control could be implemented by varying the system Hamiltonian.
According to adiabatic theorem, a slowly changing Hamiltonian can approximately
keep the system at the ground state during the evolution if the initial state
is a ground state. In this paper we consider this process as an interpolation
between the initial and final Hamiltonians. We use the mean value of a single
operator to measure the distance between the final state and the ideal ground
state. This measure could be taken as the error of adiabatic approximation. We
prove under certain conditions, this error can be precisely estimated for an
arbitrarily given interpolating function. This error estimation could be used
as guideline to induce adiabatic evolution. According to our calculation, the
adiabatic approximation error is not proportional to the average speed of the
variation of the system Hamiltonian and the inverse of the energy gaps in many
cases. In particular, we apply this analysis to an example on which the
applicability of the adiabatic theorem is questionable.Comment: 12 pages, to appear in EPJ Quantum Technolog
A posteriori teleportation ?
Braunstein and Kimble observe correctly that, in the Innsbruck experiment,
Nature 390, 575 (1997), one does not always observe a teleported photon
conditioned on a coincidence recording at the Bell-state analyser. However,
when a teleported photon appears, it has all the properties required by the
teleportation protocol.Comment: 1 page LaTeX. Reply to a comment by S.L. Braunstein and H.J. Kimble,
Nature 394, 840-841 (1998) and quant-ph/981000
Quantum Unique Ergodicity for Eisenstein Series in the Level Aspect
We prove a variety of quantum unique ergodicity results for Eisenstein series
in the level aspect. A new feature of this variant of QUE is that the main term
involves the logarithmic derivative of a Dirichlet -function on the
-line. A zero of this -function near the -line can thus have a
distorting effect on the main term.
We obtain quantitative control on the test function and thereby prove an
asymptotic formula in the level aspect version of the problem with test
functions of shrinking support. Surprisingly, this asymptotic formula shows
some obstruction to equidistribution that may retrospectively be interpreted as
being caused by the growth of Eisenstein series in the cusps. We also make some
coarse descriptions on the unevenness of the mass distribution of level
Eisenstein series on the fibers of the canonical projection map from
to .Comment: Multiple updates thanks to the referee
A Flexible Method for Conducting Power Analysis for Two- and Three-Level Hierarchical Linear Models in R
A general approach for conducting power analysis in two- and three-level hierarchical linear models (HLMs) is described. The method can be used to perform power analysis to detect fixed effects at any level of a HLM with dichotomous or continuous covariates. It can easily be extended to perform power analysis for functions of parameters. Important steps in the derivation of this approach are illustrated and numerical examples are provided. Sample code implementing this approach is provided using the free program R
Evidence for Respiratory Neuromodulator Interdependence after Cholinergic Disruption in the Ventral Respiratory Column
Reverse dialysis of the muscarinic receptor antagonist, atropine (ATR, 50 mM), into the pre-Bötzinger Complex region of the ventral respiratory column (VRC) of awake and sleeping goats increases breathing frequency and serotonin (5-HT), substance P (SP), glycine, and GABA concentrations in the effluent dialysate. Herein, we report data from goats in which we reverse dialyzed 5 mM ATR or specific antagonists of M2 or M3 muscarinic receptors into the VRC. The effects on frequency of all three antagonists were not significantly different from time control studies. 5 mM ATR and the M3 antagonist increased SP sevenfold less than 50 mM ATR. The antagonists had no effect on 5-HT, glycine, and/or GABA, suggesting that the increases in glycine and GABA with 50 mM ATR were secondary to the larger increases in 5-HT and/or SP. These data are suggestive of neuromodulator interdependence, whereby attenuation of one neuromodulator is compensated for by local changes in other neuromodulators to stabilize breathing
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