The Quantum Theory of MIMO Markovian Feedback with Diffusive Measurements

TL;DR

This paper extends the quantum Markovian feedback theory from single-input single-output systems to complex MIMO systems with multiple inputs and outputs, using vector-operator algebra to handle arbitrary diffusive measurements.

Contribution

It generalizes the SISO quantum feedback control theory to MIMO systems, incorporating multiple inputs, outputs, and diffusive measurements with a new mathematical framework.

Findings

Developed a MIMO quantum feedback control framework

Unified treatment of multiple inputs and outputs in quantum feedback

Enhanced mathematical structure using vector-operator algebra

Abstract

Feedback control engineers have been interested in MIMO (multiple-input multiple-output) extensions of SISO (single-input single-output) results of various kinds due to its rich mathematical structure and practical applications. An outstanding problem in quantum feedback control is the extension of the SISO theory of Markovian feedback by Wiseman and Milburn [Phys. Rev. Lett. {\bf 70}, 548 (1993)] to multiple inputs and multiple outputs. Here we generalize the SISO homodyne-mediated feedback theory to allow for multiple inputs, multiple outputs, and \emph{arbitrary} diffusive quantum measurements. We thus obtain a MIMO framework which resembles the SISO theory and whose additional mathematical structure is highlighted by the extensive use of vector-operator algebra.