Process tomography via sequential measurements on a single quantum system

TL;DR

This paper presents a sequential measurement protocol for quantum process tomography on a single two-level system, enabling accurate state and parameter estimation through continuous measurement updates.

Contribution

It introduces a hybrid classical-quantum estimation method that combines sequential measurements with a coupled classical system to determine quantum states and dynamics.

Findings

Demonstrates convergence of state estimates to true states

Shows effective parameter estimation via sequential measurements

Provides numerical evidence of method's accuracy

Abstract

We utilize a discrete (sequential) measurement protocol to investigate quantum process tomography of a single two-level quantum system, with an unknown initial state, undergoing Rabi oscillations. The ignorance of the dynamical parameters is encoded into a continuous-variable classical system which is coupled to the two-level quantum system via a generalized Hamiltonian. This combined estimate of the quantum state and dynamical parameters is updated by using the information obtained from sequential measurements on the quantum system and, after a sufficient waiting period, faithful state monitoring and parameter determination is obtained. Numerical evidence is used to demonstrate the convergence of the state estimate to the true state of the hybrid system.