Codice  QDD 113 
Titolo  Quantum measurements in continuous time, non Markovian evolutions and feedback 
Data  20111130 
Autore/i  Barchielli, A.; Gregoratti, M. 
Link  Download full text  Pubblicato  Philosophical Transactions of the Royal Society. Section A 
Abstract  In this paper we present a non Markovian version of quantum trajectory theory, based on the stochastic Schroedinger equation with stochastic coefficients. In this framework we can describe measurements in continuous time combined with measurement based feedback. Indeed, realistic descriptions of a feedback loop have to include delay and thus need a non Markovian theory.
As an application we consider a twolevel atom stimulated by a laser. We introduce closed loop control too, via the stimulating laser, with the aim to enhance the squeezing of the emitted light, and other typical quantum properties. Let us stress the change of point of view with respect to the usual applications of control theory. Here the system is the twolevel atom, but we do not want to control its state, to bring the atom to a final target state. Our aim is to control the Mandel Qparameter and the spectrum of the emitted light; in particular the spectrum is not a property at a single time, but involves a long interval of times (a Fourier transform of the autocorrelation function of the observed output is needed). 
