Does entanglement persist at the macroscopic level?

          @misc{ pirsa_PIRSA:10050046,
            doi = {10.48660/10050046},
            url = {https://pirsa.org/10050046},
            author = {Leggett, Anthony},
            keywords = {},
            language = {en},
            title = {Does entanglement persist at the macroscopic level?},
            publisher = {Perimeter Institute},
            year = {2010},
            month = {may},
            note = {PIRSA:10050046 see, \url{https://pirsa.org}}
          }
          

Abstract

The quantum states postulated to occur in situations of the "Schroedinger's Cat" type are essentially N-particle GHZ states with N very large compared to 1,and their observation would thus be particularly compelling evidence for the ubiquity of the phenomenon of entanglement. However, in the traditional quantum measurement literature considerable scepticism has been expressed about the observability of this kind of "macroscopically entangled" state, primarily because of the putatively disastrous effect on it of decoherence. In this talk I first examine why much of the literature has grossly overestimated the effects of decoherence,and then review the current experimental situation with respect to such states, as they (may) occur in fullerene diffraction, magnetic biomolecules, quantum-optical systems and Josephson devices; I also consider the prospects for their observation in nanomechanical systems. I conclude by reviewing and the theoretical implications of the experiments of the last decade in this area.