A strong no-go theorem on the Wigner’s friend paradox

  title={A strong no-go theorem on the Wigner’s friend paradox},
  author={Ko Bong and An{\'i}bal Utreras-Alarc{\'o}n and Farzad Ghafari and Yeong-Cherng Liang and Nora Tischler and Eric G. Cavalcanti and Geoff J. Pryde and Howard M. Wiseman},
  journal={Nature Physics},
  pages={1199 - 1205}
Does quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. Here, by building on a scenario with two separated but… 

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