%0 Journal Article
%J Systems and Control Letters, 59 (12):782-786, 2010
%D 2010
%T Feedback schemes for radiation damping suppression in NMR: a control-theoretical perspective
%A Claudio Altafini
%A Paola Cappellaro
%A David Cory
%X In NMR spectroscopy, the collective measurement is weakly invasive and its back-action is called radiation damping. The aim of this paper is to provide a control-theoretical analysis of the problem of suppressing this radiation damping. It is shown that the two feedback schemes commonly used in the NMR practice correspond one to a high gain oputput feedback for the simple case of maintaining the spin 1/2 in its inverted state, and the second to a 2-degree of freedom control design with a prefeedback that exactly cancels the radiation damping field. A general high gain feedback stabilization design not requiring the knowledge of the radiation damping time constant is also investigated.
%B Systems and Control Letters, 59 (12):782-786, 2010
%I Elsevier
%G en
%U http://hdl.handle.net/1963/4384
%1 4132
%2 Mathematics
%3 Functional Analysis and Applications
%4 -1
%$ Submitted by Andrea Wehrenfennig (andreaw@sissa.it) on 2011-09-30T10:33:33Z\\nNo. of bitstreams: 1\\nAlCaCo09.pdf: 172729 bytes, checksum: b8f2ae1517b057b5f24fd2d8b3666002 (MD5)
%R 10.1016/j.sysconle.2010.09.004
%0 Report
%D 2007
%T Feedback control of spin systems
%A Claudio Altafini
%X The feedback stabilization problem for ensembles of coupled spin 1/2 systems is discussed from a control theoretic perspective. The noninvasive nature of the bulk measurement allows for a fully unitary and deterministic closed loop. The Lyapunov-based feedback design presented does not require spins that are selectively addressable. With this method, it is possible to obtain control inputs also for difficult tasks, like suppressing undesired couplings in identical spin systems.
%B Quantum Inf. Process. 6 (2007) 9-36
%G en_US
%U http://hdl.handle.net/1963/1808
%1 2406
%2 Mathematics
%3 Functional Analysis and Applications
%$ Submitted by Andrea Wehrenfennig (andreaw@sissa.it) on 2006-04-12T07:08:54Z\\nNo. of bitstreams: 1\\nquant-ph0601016.pdf: 557249 bytes, checksum: 7285125f31ec5e7e75c04033506d986b (MD5)
%R 10.1007/s11128-006-0038-x
%0 Journal Article
%J 45th IEEE Conference on Decision and Control (2007) 2471-2476
%D 2007
%T Feedback stabilization of quantum ensembles: a global convergence analysis on complex flag manifolds
%A Claudio Altafini
%X In an N-level quantum mechanical system, the problem of unitary feedback stabilization of mixed density operators to periodic orbits admits a natural Lyapunov-based time-varying feedback design. A global description of the domain of attraction of the closed-loop system can be provided based on a \\\"root-space\\\"-like structure of the space of density operators. This convex set foliates as a complex flag manifold where each leaf is identified with the coadjoint orbit of the eigenvalues of the density operator. The converging conditions are time-independent but depend from the topology of the flag manifold: it is shown that the closed loop must have a number of equilibria at least equal to the Euler characteristic of the manifold, thus imposing obstructions of topological nature to global stabilizability.
%B 45th IEEE Conference on Decision and Control (2007) 2471-2476
%G en_US
%U http://hdl.handle.net/1963/1729
%1 2422
%2 Mathematics
%3 Functional Analysis and Applications
%$ Submitted by Andrea Wehrenfennig (andreaw@sissa.it) on 2006-01-30T13:15:57Z\\nNo. of bitstreams: 1\\nquant-ph0506268.pdf: 339036 bytes, checksum: 0deeffc30853814638abac71df2a136d (MD5)
%R 10.1109/CDC.2006.377774
%0 Journal Article
%J IEEE Trans. Automatic Control 47 (2002) 1551-1556
%D 2002
%T Following a path of varying curvature as an output regulation problem
%A Claudio Altafini
%X Given a path of nonconstant curvature, local asymptotic stability can be proven for the general n trailer whenever the curvature can be considered as the output of an exogenous dynamical system. The controllers that provide convergence to zero of the tracking error chosen for the path-following problem are composed of a prefeedback that input-output linearizes the system, plus a linear controller.
%B IEEE Trans. Automatic Control 47 (2002) 1551-1556
%I IEEE
%G en_US
%U http://hdl.handle.net/1963/3143
%1 1190
%2 Mathematics
%3 Functional Analysis and Applications
%$ Submitted by Andrea Wehrenfennig (andreaw@sissa.it) on 2008-10-20T11:01:46Z\\nNo. of bitstreams: 1\\nfollowing.pdf: 236416 bytes, checksum: c98dbcaee3416675cc45749d7af72bb6 (MD5)
%R 10.1109/TAC.2002.802750