Flow of non-classical correlations in cluster states due to projective measurements

TL;DR

This paper investigates how non-classical correlations, including entanglement and quantum discord, evolve in cluster states on ladder graphs during measurements, revealing dependence on measurement type and ladder length, with implications for measurement-based quantum computing.

Contribution

It demonstrates that non-classical correlations in ladder cluster states increase with ladder length after measurements, especially when non-Clifford measurements are performed, providing insights into quantum correlation dynamics in MBQC.

Findings

Correlations strengthen with ladder length after measurements.

Clifford basis measurements do not produce non-classical correlations.

Non-Clifford measurements influence correlation development based on their number and position.

Abstract

We explore the flow of quantum correlations in cluster states defined on ladder type graphs as measurements are done on qubits located on the nodes of the cluster. We focus on three qubits at the end of the ladder and compute the non-classical correlations between two of the three qubits as measurements are done on the remaining qubits. We compute both the entanglement between the two qubits as well as the quantum discord between them after the measurements. We see that after all but three qubits are measured, the non-classical correlations developed between two of them show a trend of being stronger with the length of the ladder. It is also seen that measurements on to the basis states of operators belonging to the Clifford group do not produce such correlations or entanglement. The non-classical correlations produced depend only on the number, location and nature of preceding non-Clifford measurements. Our results not only throw light on the dynamics of quantum correlations while an algorithm proceeds step-by-step in the Measurement-based Based Quantum Computing (MBQC) model but it also reveals how the last two qubits, treated as an open quantum system, can have increasing entanglement or other non-classical correlations as its immediate environment is interrogated through random measurements.