Measuring bipartite quantum correlations of an unknown state

Area of Science:

• Quantum Information Science
• Quantum Optics
• Nuclear Magnetic Resonance

Background:

• Characterizing quantum correlations is crucial for quantum information processing.
• Traditional methods like quantum state tomography require extensive measurements, scaling poorly with system size.
• Evaluating quantum correlations without full state information is a significant challenge.

Purpose of the Study:

• To experimentally measure bipartite quantum correlations of an unknown two-qubit state.
• To introduce and validate a method using geometric discord for efficient correlation evaluation.
• To demonstrate an advantage over full state tomography for larger quantum systems.

Main Methods:

• Utilized a liquid state Nuclear Magnetic Resonance (NMR) setup.
• Employed geometric discord to quantify quantum correlations.
• Performed experimental measurements without prior knowledge of the density matrix.

Main Results:

• Successfully measured bipartite quantum correlations for an unknown two-qubit state.
• Demonstrated that the geometric discord method requires fewer measurements than full state tomography for 2 ⊗ d systems.
• Observed sudden transitions in quantum correlations under local phase and amplitude damping channels.
• Measured the negativity of quantumness for reference.

Conclusions:

• The geometric discord approach provides an efficient method for quantifying quantum correlations in multipartite systems.
• This technique offers a scalable alternative to quantum state tomography.
• The observed sudden transitions highlight the fragility of quantum correlations under noise.