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Emergent classicality in general multipartite states and channels

Date : Wednesday, November 25th, 2020 10:30 - 12:00 Place : https://sites.google.com/view/cevis2020/registration (We will send the zoom link to the registered participants) Lecturer : Xiao-Liang Qi Affiliation : Stanford University Committee Chair : Masaki Oshikawa (ex.63275)
e-mail: oshikawa@issp.u-tokyo.ac.jp

In a quantum measurement process, classical information about the measured system spreads throughout the environment. Meanwhile, quantum information about the system becomes inaccessible to local observers. Here we prove a result about quantum channels indicating that an aspect of this phenomenon is completely general. We show that for any evolution of the system and environment, for everywhere in the environment excluding an O(1)-sized region we call the “quantum Markov blanket,” any locally accessible information about the system must be approximately classical, i.e. obtainable from some fixed measurement. The result strengthens the earlier result of Brandao et al. (Nat. comm. 6:7908 ) in which the excluded region was allowed to grow with total environment size. It may also be seen as a new consequence of the principles of nocloning or monogamy of entanglement. Our proof offers a constructive optimization procedure for determining the “quantum Markov blanket” region, as well as the effective measurement induced by the evolution. Alternatively, under channel-state duality, our result characterizes the marginals of multipartite states.

Reference: https://arxiv.org/abs/2001.01507

Chair: Gil Young Cho

This event is jointly organized by the Korea Institute for Advanced Study and the University of Tokyo. “Correlated Electrons Virtual International Seminars (CEVIS)” https://sites.google.com/view/cevis2020/home

(Published on: Wednesday November 25th, 2020)