Realization and characterization of a two-photon four-qubit linear cluster state.

Area of Science:

• Quantum Information Science
• Experimental Quantum Physics

Background:

• Quantum entanglement is a key resource for quantum information processing.
• Linear cluster states are essential multipartite entangled states for quantum computing and communication.

Purpose of the Study:

• To experimentally realize a four-qubit linear cluster state.
• To demonstrate a novel proof of quantum nonlocality using this state.

Main Methods:

• Generating entanglement between two photons in both polarization and linear momentum degrees of freedom.
• Performing quantum state tomography to characterize the generated state.
• Evaluating an entanglement witness to confirm multipartite entanglement.

Main Results:

• Successful experimental realization of a four-qubit linear cluster state.
• Demonstration of a novel "stronger two observer all-versus-nothing" test of quantum nonlocality.
• Validation of the generated state's properties through tomographic measurements.

Conclusions:

• The experimental creation of the four-qubit linear cluster state is a significant step in quantum information science.
• The developed nonlocality test offers a more robust method for verifying quantum correlations.
• This work paves the way for advanced quantum communication and computation protocols.