Searcharxiv⌕ Search

arXiv subjects

Lajos Diósi

Publications and source records attributed to Lajos Diósi.

77 records · Page 5Linked to original sources
arXiv2002

Estimating the post-measurement state

We study generalized measurements (POVM measurements) on a single d-level quantum system which is in a completely unknown pure state, and derive the best estimate of the post-measurement state. The mean post-measuremement estimation fidelity of a generalized measurement is obtained and related to the operation fidelity of the device. This illustrates how the information gain about the post-measurement state and the corresponding state disturbance are mutually dependent. The connection between the best estimates of the pre- and post-measurement state is established and interpreted. For pure generalized measurements the two states coincide.

quant-ph↗
arXiv1999

Non-Markovian quantum state diffusion: Perturbation approach

We present a perturbation theory for non-Markovian quantum state diffusion (QSD), the theory of diffusive quantum trajectories for open systems in a bosonic environment [Physical Review {\bf A 58}, 1699, (1998)]. We establish a systematic expansion in the ratio between the environmental correlation time and the typical system time scale. The leading order recovers the Markov theory, so here we concentrate on the next-order correction corresponding to first-order non-Markovian master equations. These perturbative equations greatly simplify the general non-Markovian QSD approach, and allow for efficient numerical simulations beyond the Markov approximation. Furthermore, we show that each perturbative scheme for QSD naturally gives rise to a perturbative scheme for the master equation which we study in some detail. Analytical and numerical examples are presented, including the quantum Brownian motion model.

quant-ph↗
arXiv1994

Permanent State Reduction: Motivations, Results, and By-Products

We enlist various motivations underlying the idea that von Neumann collapses occure permanently, spontaneously and even universally. In addition to the conceptual value of permanent reduction theory, we mention its important by-product promoting new quantum Monte-Carlo simulations of irrevesible quantum processes, especially in laser optics.

cond-mat↗
arXiv1994

Comments on Omnès' Model for Uniqueness of Data

Standard methods of the theory of permanent state reduction are shown to offer an alternative realization of Omnès' project. Our proposal, as simple as Omnès' one, possesses closed master equation for the ensemble density operator, assuring causality.

gr-qc↗