On observability of N-level quantum systems

Andrzej Jamiołkowski

Mikhail S. Ananyevskiy, Аlexander L. Fradkov

Zibo Miao, Luis A. Duffaut Espinosa, Ian R. Petersen +2 more

The purpose of this paper is to find coherent quantum observers for open n-level quantum systems. Recently, a class of linear coherent observers has been developed for quantum harmonic oscillators. However, open n-level quantum systems, which are characterized by bilinear quantum stochastic differential equations, escape the realm of the known theory. Therefore, in this paper we show how a coherent quantum observer is designed to track the corresponding n-level quantum plant asymptotically in the sense of mean values. We also discuss suboptimal quantum observers in the sense of least mean squares estimation.

A. R. P. Rau, Weichang Zhao

Ian R. Petersen

This paper considers the problem of constructing a direct coupling quantum observer for a single qubit finite level quantum system plant. The proposed observer is a single mode linear quantum system which is shown to be able to estimate one of the plant variables in a time averaged sense.

Vladimir A. Namiot, Ljudmila Yu. Shchurova

Abstract—The issue of how observation of a process in quantum mechanics may influence its outcome is described by case studies of quantum emission by a two-level system and the passage of a particle through a potential barrier. In the first case, the observation can reduce the probability of quantum emission by the two-level system (the quantum Zeno effect). In the second case, the observation of a particle can significantly increase the probability for a particle to pass through a barrier, sometimes even by many orders of magnitude (the barrier anti-Zeno effect). The possibility of such effects in biological systems is discussed.