# Optimal nonlinear filtering of quantum state

## TL;DR

This paper extends optimal filtering theory to quantum processes, proposing a model for indirect measurements on a qudit system to improve quantum state estimation.

## Contribution

It introduces a quantum filtering equation based on an indirect measurement model for qudits, expanding classical filtering to quantum systems.

## Key findings

- Derived a quantum filtering equation for indirect measurements
- Proposed an observation model for single qudit systems
- Enhanced quantum state estimation techniques

## Abstract

We extend the optimal filtering equation known from the Stratonovich filtering theory on the quantum process case. The used observation model is based on an indirect measurement method, where the measurement is performed on an ancilla system that is interacted with an unknown one. Observation model for single qudit system is proposed.