ITP-quantumseminare September 2020

itp-quantumseminare@lists.phys.ethz.ch

1 participants
4 discussions

QIT Seminar tomorrow
by Joe Renes 28 Sep '20

28 Sep '20

Hi all, Tomorrow Almudena will tell us about her latest paper, https://arxiv.org/abs/2009.04484. Join us at 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, -joe

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Tomorrow's QIT Seminar
by Joe Renes 21 Sep '20

21 Sep '20

Hi all, Tomorrow at 2pm Qiushi Liu will tell us about his master's thesis, entitled "Quantum Fisher Information Dynamics in Quantum Neural Networks and Information Scrambling". See below for the abstract. Zoom link: https://ethz.zoom.us/j/362994444. Best, -joe Abstract: Quantum Fisher information (QFI) is a central concept in the context of quantum metrology. It could be geometrically interpreted as a measure of the statistical distance between neighbouring quantum states, which makes QFI closely connected to a variety of fields in physics. In this thesis, we use QFI to characterize the flow of quantum information in quantum circuits. In particular, we consider the task of learning the optimal measurement for quantum metrology using variational quantum circuits. We empirically observe an intriguing phenomenon that the learning process is split into two stages. In the first stage the training cost undergoes a fast decrease while QFI is locally accumulated. In the second stage, the neural network slightly improves its performance with a slow decrease of local QFI, implying a global scrambling behaviour. This information-theoretic view opens a path to understanding the internal mechanism of quantum machine learning. We furthermore demonstrate that QFI is a natural quantity to detect scrambling and establish a connection between QFI and the out-of-time-order correlation (OTOC) function.

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tomorrow's QIT seminar: 2pm
by Joe Renes 14 Sep '20

14 Sep '20

Hi all, Tomorrow we switch to the new time of the QIT seminar, 2pm. The zoom link remains the same, https://ethz.zoom.us/j/362994444. Alberto Rolandi will present his master thesis, supervised by Henrik, entitled "Extensivity of Rényi Entropies in Many-Body Systems". Here is the abstract: We prove the approximate sub-additivity of min-entropies in Gibbs states above a universal threshold temperature up to boundary terms. Under the further assumption of extensive free energy, we establish that there exist subsystems with extensive Rényi entropies. Second, we study the Rényi entanglement entropies for disconnected subsystems in spin-chains described by generic (gapped), translational invariant matrix product states. We provide an explicit lower-bound to the Rényi entropy densities of the subsystem consisting of every k-th spin in the thermodynamic limit. As a side-result, we obtain a lower bound for the expansion coefficient of a unital primitive quantum channel in terms of its Kraus-rank. Best, -joe

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no meeting tomorrow / new time next week
by Joe Renes 07 Sep '20

07 Sep '20

Hi all, We have a little break in the calendar this week --- no meeting tomorrow. Next week we will start at the new time for the fall semester, 2pm Tuesdays, with a talk by Alberto Rolandi. He'll report on his master thesis with Henrik. I'll send around the details of the talk next week. Best, -joe

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ITP-quantumseminare September 2020