ITP-quantumseminare

itp-quantumseminare@lists.phys.ethz.ch

2 participants
1384 discussions

tomorrow's group meeting
by Joe Renes 19 Oct '20

19 Oct '20

Hi all, Tomorrow we have a guest talk by Xavier Coiteux-Roy, from Stefan Wolf's group at USI in Lugano, with the title "Information-theoretic security from Landauer’s principle". See below for the abstract. The zoom link (same as every week) is https://ethz.zoom.us/j/362994444. Best, -joe %%%%%% Abstract: Information-theoretic security is largely physical; The security of cryptographic protocols can be based, and has been based, on diverse physical assumptions. Amongst them, most notably, quantum mechanics. But also, the fatality of noise in communication channels, the difficulty of storing very large information strings, special relativity... What about thermodynamics? To address that question, I will present a theoretical model: a classical-information world where large randomized memories are accessible and reversible computation is effortless, but energy is severely limited. I will present in that world two information-theoretically secure protocols; they realize universal primitives for secure communication and secure multipartite computation (i.e., secret key establishment and 1–2 oblivious transfer). I will finish by debunking the security of those protocols in a world where information is not classical, but contextual — however, differently than according to quantum mechanics. The security in a quantum mechanical world of those two protocols is still unknown.

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today's talk (3pm)
by Joe Renes 13 Oct '20

13 Oct '20

Hi all, Just a follow-up to yesterday's email. Here's the title and abstract for today's talk: Title: 3-locality in the Triangle Network Abstract: The triangle network has been discussed a lot in recent years as one possible way of generalizing Bell inequalities. It has been shown to inhibit a new type of nonlocality different from Bell inequalities that seems to be inherent to the network structure. In this talk I will present one of the possible approaches that have been tried to determine whether the correlations, resulting from a natural type of measurement proposed by Nicolas Gisin, are nonlocal. Best, -joe

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tomorrow's QIT Seminar: 3pm
by Joe Renes 12 Oct '20

12 Oct '20

Hi all, Tomorrow Julian Lang will tell us about his master thesis with Elisa. Note that we start at 3pm, not at 2pm. I will send the title and abstract when they are available. https://ethz.zoom.us/j/362994444. Best, -joe

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tomorrow's QIT Seminar
by Joe Renes 05 Oct '20

05 Oct '20

Hi all, Tomorrow we'll hear from Christophe Piveteau, who has just completed his master's thesis at IBM. He'll speak about "Advanced Methods for Quasiprobabilistic Quantum Error Mitigation", see the abstract below. We meet at 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, -joe Abstract: Current quantum computers are plagued by prohibitive amounts of noise, which complicates the experimental realization of useful quantum algorithms that outperform classical computers. Quantum error mitigation techniques could constitute a potential avenue to demonstrate this feat without the need for fault-tolerant quantum error correction. One method in this family of mitigation techniques is the quasiprobability method introduced by Temme et al.. It simulates a noise-free quantum computer with a noisy one, with the caveat of only producing the correct expected values of measurement observables. The cost of a quasiprobability simulation manifests as a sampling overhead which scales exponentially in the number of error-mitigated gates in the circuit. In this thesis we aim to reduce the exponential basis of that overhead, which in turn allows the application of the quasiprobability method to deeper quantum circuits. A central result is the introduction of a novel scheme, which we call Stinespring algorithm, that aims to choose the quasiprobability decomposition in a noise-aware manner.

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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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tomorrow's group meeting 1500
by Joe Renes 31 Aug '20

31 Aug '20

Hi all, Tomorrow Yanglin Hu will tell us about his semester project, entitled "Confined Relativistic Quantum Clock". See below for the abstract. The zoom link is https://ethz.zoom.us/j/362994444. Best, -joe Title: Confined Relativistic Quantum Clock Abstract: A potentially detectable quantum modification to time in delocalised clocks are proposed previously in order to examine the correctness of quantum gravity theory. Here we aim to further investigate the possibility to design an experiment. We derive the Hamiltonian of a relativistic quantum clock in the electromagnetic field in the Rindler spacetime. Based on that, we calculate the time dilation of a quantum clock in a Penning trap. The numerical result shows that the time dilation is detectable for a confined quantum clock. We also explore the effect of decoherence via a heat bath of harmonic oscillators on a free quantum clock. The decoherence does not change the time average of the clock. Results till now show that designing an experiment to detect the quantum modification to time are a possibility.

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tomorrow's group meeting at 15:00
by Joe Renes 24 Aug '20

24 Aug '20

Hi all, Tomorrow Sven Jandura will tell us about his semester project at IBM, entitled "Time Propagation of a Wave Packet using a Variational Quantum Simulator". See below for the abstract. The zoom link is https://ethz.zoom.us/j/362994444. Best, -joe Abstract: Quantum computers can speed up the calculation of the time evolution of quantum states, a task that is classically hard because just storing the wavefunction of a state of multiple particles requires resources exponential in the number of particles. Here we present a variational hybrid quantum-classical algorithm based on McLachlans variational principle that approximates the time evolution of particles moving in arbitrary potentials. We then numerically study the performance of this algorithm on a free Gaussian wave packet in one dimension and the scattering of a Gaussian wave packet on an Eckart barrier. We find that for a free particle the number of parameters in the variational form used by us can be significantly smaller than the real dimension of the Hilber space, while for the Eckart barrier it has to be close to the real dimension of the Hilbert space to obtain an high fidelity approximation.

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ITP-quantumseminare