Exploring quantum properties of bipartite mixed states under coherent and incoherent basis

TL;DR

This paper investigates how the choice of basis affects the measurement of quantum coherence and entanglement in bipartite mixed states, highlighting that coherence should be measured in a separable basis for accurate results.

Contribution

It demonstrates that quantum coherence should be estimated in a separable basis, while entanglement and mixedness can be measured in any basis, and explores their implications for teleportation and nonlocality.

Findings

Coherence measured in Bell basis does not reflect true coherence.

Teleportation can succeed without Bell-CHSH inequality violation.

Quantum nonlocality is not necessary for quantum teleportation.

Abstract

Quantum coherence and quantum entanglement are two different manifestations of the superposition principle. In this article we show that the right choice of basis to be used to estimate coherence is the separable basis. The quantum coherence estimated using the Bell basis does not represent the coherence in the system, since there is a coherence in the system due to the choice of the basis states. We first compute the entanglement and quantum coherence in the two qubit mixed states prepared using the Bell states and one of the states from the computational basis. The quantum coherence is estimated using the l1-norm of coherence, the entanglement is measured using the concurrence and the mixedness is measured using the linear entropy. Then we estimate these quantities in the Bell basis and establish that coherence should be measured only in separable basis, whereas entanglement and mixedness can be measured in any basis. We then calculate the teleportation fidelity of these mixed states and find the regions where the states have a fidelity greater than the classical teleportation fidelity. We also examine the violation of the Bell-CHSH inequality to verify the quantum nonlocal correlations in the system. The estimation of the above mentioned quantum correlations, teleportation fidelity and the verification of Bell-CHSH inequality is also done for bipartite states obtained from the tripartite systems by the tracing out of one of their qubits. We find that for some of these states teleportation is possible even when the Bell-CHSH inequality is not violated, signifying that nonlocality is not a necessary condition for quantum teleportation.