The Dual Roles of Quantum Discord in a Non-demolition Probing Task

TL;DR

This paper investigates a non-demolition quantum probing task where quantum discord plays dual roles, showing how quantum correlations influence information extraction without disturbing the quantum state.

Contribution

It establishes necessary and sufficient conditions on Hamiltonians for non-demolition probing and reveals the dual roles of quantum discord in such processes.

Findings

Probing preserves the quantum state and is independent of initial probing state.

One side of the system remains discord-free, while the other side develops discord during probing.

Maximal information extraction requires quantum discord to approach zero.

Abstract

We present a non-demolition quantum information processing task of probing the information of a class of quantum state. In this task, the information is extracted by some unitary evolution with the introduced probing qubit assisted, but the probed quantum state (density matrix) is undisturbed at any time and independent of the choice of the initial probing state. We give a sufficient and necessary condition on the Hamiltonian that can lead to the successful realization of such a task. We prove that, for any feasible scheme, the probed plus probing system will always stay at a disentangled state with one side quantum discord absent and the other side one inevitably produced in the probing process. An explicit example is given for the demonstration, whilst the example shows that the ratio of quantum discord to the total correlation will have to reduce to zero for the maximal accessible information. In this sense, we say that quantum discord plays the dual roles in this case.