Baumann Veronika
Atominstitut, Technische Universität Wien, 1020 Vienna, Austria.
Institute for Quantum Optics and Quantum Information (IQOQI), Boltzmanngasse 3, 1090 Vienna, Austria.
Entropy (Basel). 2023 Oct 6;25(10):1420. doi: 10.3390/e25101420.
The famous Wigner's friend experiment considers an observer-the friend-and a superobserver-Wigner-who treats the friend as a quantum system and her interaction with other quantum systems as unitary dynamics. This is at odds with the friend describing this interaction via collapse dynamics, if she interacts with the quantum system in a way that she would consider a measurement. These different descriptions constitute the Wigner's friend paradox. Extended Wigner's friend experiments combine the original thought experiment with non-locality setups. This allows for deriving local friendliness inequalities, similar to Bell's theorem, which can be violated for certain extended Wigner's friend scenarios. A Wigner's friend paradox and the violation of local friendliness inequalities require that no classical record exists, which reveals the result the friend observed during her measurement. Otherwise, Wigner agrees with his friend's description and no local friendliness inequality can be violated. In this article, I introduce classical communication between Wigner and his friend and discuss its effects on the simple as well as extended Wigner's friend experiments. By controlling the properties of a (quasi) classical communication channel between Wigner and the friend, one can regulate how much outcome information about the friend's measurement is revealed. This gives a smooth transition between the paradoxical description and the possibility of violating local friendliness inequalities, on the one hand, and the effectively collapsed case, on the other hand.
著名的维格纳朋友实验考虑了一个观察者——朋友，以及一个超级观察者——维格纳，维格纳将朋友视为一个量子系统，并将她与其他量子系统的相互作用视为幺正动力学。如果朋友以她认为是测量的方式与量子系统相互作用，那么这与她通过坍缩动力学描述这种相互作用相矛盾。这些不同的描述构成了维格纳朋友悖论。扩展的维格纳朋友实验将原始思想实验与非定域性设置相结合。这使得可以推导出类似于贝尔定理的局部友好性不等式，对于某些扩展的维格纳朋友场景，这些不等式可能会被违反。维格纳朋友悖论以及局部友好性不等式的违反要求不存在经典记录，该记录揭示朋友在测量期间观察到的结果。否则，维格纳会同意他朋友的描述，并且不会违反局部友好性不等式。在本文中，我引入了维格纳和他朋友之间的经典通信，并讨论了其对简单以及扩展的维格纳朋友实验的影响。通过控制维格纳和朋友之间（准）经典通信信道的属性，人们可以调节关于朋友测量结果的信息被揭示的程度。这一方面在矛盾描述和违反局部友好性不等式的可能性之间，另一方面在有效坍缩的情况之间给出了平滑过渡。
