ITP-quantumseminare

itp-quantumseminare@lists.phys.ethz.ch

1 participants
1357 discussions

link to recorded videos
by Joe Renes 02 Nov '20

02 Nov '20

Hi all, Here is the link to the video recordings of previous seminars: https://share.phys.ethz.ch/~lecture/renes/QIT%20Seminar/ You will need to enter your ethz username and password (not d-phys). Best, -joe

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Tomorrow's group meeting 2pm
by Joe Renes 02 Nov '20

02 Nov '20

Hi all, Tomorrow Yuxiang will give a more detailed look at his recent research. See below for title and abstract. The zoom link is https://ethz.zoom.us/j/362994444. Best, -joe Title: Optimal universal programming of unitary gates Abstract: A universal quantum processor is a device that takes as input a (quantum) program, containing an encoding of an arbitrary unitary gate, and a (quantum) data register, on which the encoded gate is applied. While no perfect universal quantum processor can exist, approximate processors have been proposed in the past two decades. A fundamental open question is how the size of the smallest quantum program scales with the approximation error. Here we answer the question, by proving a bound on the size of the program and designing a concrete protocol that attains the bound in the asymptotic limit. Our result is based on a connection between optimal programming and the Heisenberg limit of quantum metrology, and establishes an asymptotic equivalence between the tasks of programming, learning, and estimating unitary gates. This talk will be based on https://arxiv.org/abs/2007.10363.

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no QIT seminar this week
by Joe Renes 26 Oct '20

26 Oct '20

Hi all, In view of the department evaluation this week, there will be no QIT Seminar tomorrow. Best, -joe

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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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ITP-quantumseminare