Light-based test spots entanglement in more than two qubits

P. Rosario of Universidade Federal de São Carlos and CESQ/ISIS, CNRS and Université de Strasbourg, along with R. Bachelard of Universidade Federal de São Carlos, introduced electric-field based inequalities capable of detecting multilevel entanglement in systems of N quantum emitters. The researchers determined that the polarization channel and direction of detection can enhance entanglement detection, a feature specific to multilevel systems. They demonstrated the efficiency of these new witnesses by applying them to Dicke states, singlet states and W-like states, finding the detection is robust to noise and applicable to mixed entangled states. These findings open possibilities for detecting entanglement without local measurements in systems like superconducting qubits, Rydberg atoms, or quantum dots. Electric-field based inequalities now allow detection of entanglement in systems containing an arbitrary number of quantum emitters, a step beyond previous methods largely focused on two-particle entanglement. This new approach uses light polarization as a key element, enhancing the ability to identify entanglement…