Measuring bipartite quantum correlations of an unknown state

TL;DR

This paper demonstrates an experimental method to measure bipartite quantum correlations in unknown two-qubit states using NMR, avoiding full state tomography and revealing phenomena like sudden transitions under noise.

Contribution

It introduces a scalable, measurement-efficient approach to quantify quantum correlations in unknown states without prior state knowledge.

Findings

Quantum correlations measured without full state tomography

Method applicable to any (2 x d) system

Observation of sudden transition phenomena in quantum correlations

Abstract

We report the experimental measurement of bipartite quantum correlations of an unknown two-qubit state. Using a liquid state Nuclear Magnetic Resonance (NMR) setup and employing geometric discord, we evaluate the quantum correlations of a state without resorting to prior knowledge of its density matrix. The method is applicable to any (2 x d) system and provides, in terms of number of measurements required, an advantage over full state tomography scaling with the dimension d of the unmeasured subsystem. The negativity of quantumness is measured as well for reference. We also observe the phenomenon of sudden transition of quantum correlations when local phase and amplitude damping channels are applied to the state.