3 research outputs found
Information, disturbance and Hamiltonian quantum feedback control
We consider separating the problem of designing Hamiltonian quantum feedback
control algorithms into a measurement (estimation) strategy and a feedback
(control) strategy, and consider optimizing desirable properties of each under
the minimal constraint that the available strength of both is limited. This
motivates concepts of information extraction and disturbance which are distinct
from those usually considered in quantum information theory. Using these
concepts we identify an information trade-off in quantum feedback control.Comment: 13 pages, multicol Revtex, 2 eps figure
Feedback-control of quantum systems using continuous state-estimation
We present a formulation of feedback in quantum systems in which the best
estimates of the dynamical variables are obtained continuously from the
measurement record, and fed back to control the system. We apply this method to
the problem of cooling and confining a single quantum degree of freedom, and
compare it to current schemes in which the measurement signal is fed back
directly in the manner usually considered in existing treatments of quantum
feedback. Direct feedback may be combined with feedback by estimation, and the
resulting combination, performed on a linear system, is closely analogous to
classical LQG control theory with residual feedback.Comment: 12 pages, multicol revtex, revised and extende
Transition Probability (Fidelity) and Its Relatives
Transition Probability (fidelity) for pairs of density operators can be
defined as "functor" in the hierarchy of "all" quantum systems and also within
any quantum system. The introduction of "amplitudes" for density operators
allows for a more intuitive treatment of these quantities, also pointing to a
natural parallel transport. The latter is governed by a remarkable gauge theory
with strong relations to the Riemann-Bures metric.Comment: Talk at the 2009 Vaexoe Quantum Theory Conference. 11 page