Sommaire:

Entanglement is a property of quantum objects in which their state cannot simply be described by the sum of the individual states of their components. One difficulty faced in the study of the fundamental properties of entangled states is that the mathematical complexity of the description increases exponentially with the number of entangled subsystems. Moreover, experimental procedures to reconstruct an entangled state may require an enormous number of measurements, which necessitates a significant amount of resources and time. For instance, the reconstruction of a quantum state with five subsystems requires approximately one thousand measurements, and the reconstruction of a quantum state with ten subsystems requires more than one million measurements. Furthermore, the fragility of a quantum state increases with the number of subsystems, making the complete characterization of these systems practically impossible. Here, we test a novel idea of how to partially characterize a multipartite quantum state with a reduced number of measurements in the laboratory.


We employ an optical setup in which photon pairs are generated using a 325-nm laser to create three- and four-partite states. We find that the number of measurements required scales only linearly with the number of subsystems instead of exponentially, as in the case of a full characterization. Our method is based on the reconstruction of the local states of the subsystems without measuring the correlations between them. Surprisingly, in many cases, it is still possible to determine if the state exhibits genuine multipartite entanglement. We prepare and test quantum states of photons pertaining to different classes of entanglement. We find that this local characterization works not only for the ideal case of pure states but also for states that are moderately mixed because of experimental noise.

We expect that this type of partial characterization will be useful for quantum information applications that use certain entangled states as a resource.

Pour plus d'informations, merci de contacter Parmeggiani A.