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SC Seminar Jurriaan Buist (CWI)

  • 2021-03-25T15:00:00+01:00
  • 2021-03-25T16:00:00+01:00
March 25 Thursday

Start: 2021-03-25 15:00:00+01:00 End: 2021-03-25 16:00:00+01:00

online

Join Zoom Meeting
https://cwi-nl.zoom.us/j/86539157750?pwd=aUZld01lY0pFQXZBM20vcDgxa3hFQT09

Jurriaan Buist (CWI): Energy conservation for the one-dimensional two-fluid model for two-phase pipe flow

The one-dimensional two-fluid model (TFM) is a simplified model for multiphase flow in pipes. It is derived from a spatial averaging process, which introduces a closure problem concerning the wall and interface friction terms, similar to the closure problem in turbulence. To tackle this closure problem, we have approximated the friction terms by neural networks trained on data from DNS simulations.

Besides the closure problem, the two-fluid model has a long-standing stability issue: it is only conditionally well-posed. In order to tackle
this issue, we analyze the underlying structure of the TFM in terms of the energy behavior. We show the new result that energy is an inherent
'secondary' conserved property of the mass and momentum conservation equations of the model. Furthermore, we develop a new spatial
discretization that exactly conserves this energy in simulations.

The importance of structure preservation, and the core of our analysis, is not limited to the TFM. Neural networks that approximate physical
systems can also be designed to preserve the underlying structure of a PDE. In this way, physics-informed machine learning can yield more
physical results.

Lectures by Harry Buhrman and Léo Ducas at Quantum Symposium of Dutch Payments Association

  • 2021-03-25T14:00:00+01:00
  • 2021-03-25T16:00:00+01:00
March 25 Thursday

Start: 2021-03-25 14:00:00+01:00 End: 2021-03-25 16:00:00+01:00

At the 2021 Quantum Symposium of the Dutch Payments Association, two CWI speakers will give a lecture on the latest developments: Harry Burhman (CWI, UvA, QuSoft) and Léo Ducas (CWI). The conference specifically focuses on quantum computing and security topics with contributions from academic researchers, representatives from the banking industry and authorities in their work area.
The event gives a brief update on developments related to quantum computing, explores opportunities, prepares for the advent of the quantum computer and aims to strengthen the dialogue between the academic and industry community.

Abstracts of the CWI contributions:
* Quantum algoritmes – Prof. Harry Buhrman (CWI, UvA and QuSoft)
Quantum computers promise to have a great impact on how we do information processing tasks. The extra power comes the quantum mechanical effects of superposition, interference, and entanglement. Quantum computers require a fundamentally different hardware. The basic building block is a the qubit and operations on these qubits are fundamentally different from the operations that one performs on classical bits. Hence the software that runs on quantum computers is also fundamentally different from the way we are used to program computers. A major driving (research) question is the following: For which computational problems does a quantum computer have an advantage and how big is that advantage? This question is deeply intertwined with fundamental questions in computer science and only a partial answer has been found so far.
Recent years has seen great progress in the fabrication of reasonably stable qubits: 50-100 qubits are available now, with a projected growth to a 1000 qubits within the next 5 years. These qubits however are physical qubits that deteriorate and decohere over time. It is known that error correction in combination with fault tolerant computation offer a solution to this decoherence problem. However, this comes at a the price of using a multitude of physical qubits to implement a single stable or logical qubit. This overhead is at the moment and in the near future prohibitively large. We therefore have to develop applications for quantum computers that have a relatively large amount of qubits that decohere over time. I will describe what the impact of the above considerations is on the design of quantum algorithms.

* Quantum resistant cryptography: Standardization and Recommendation - Dr. Léo Ducas (Centrum Wiskunde & Informatica)
'In this talk, I first introduce quantum-resistant cryptography, (a.k.a. post-quantum cryptography), explain why it is needed very soon, and explain its difference with quantum cryptography. I then overview the ongoing standardization process of NIST (US National Institute for Standards and Technology), and summarize the pros and cons of the expected portfolio of standards. I conclude with a few recommendations for a safe and orderly transition to security against the cautioned advent of quantum-capable adversaries.'

For more information please visit the website.

QuSoft Seminar: Xiaoliang Qi (Stanford)

  • 2021-03-19T16:30:00+01:00
  • 2021-03-19T17:30:00+01:00
March 19 Friday

Start: 2021-03-19 16:30:00+01:00 End: 2021-03-19 17:30:00+01:00

Everyone is welcome to attend online the QuSoft seminar, this week with Xiaoliang Qi (Stanford) on 'Quantum Algorithmic Measurement'.

Abstract:
Can quantum computational tools enhance the precision and efficiency of physical experiments? Promising examples are known, but a systematic treatment and comprehensive framework are missing. We introduce Quantum Algorithmic Measurements (QUALMs) to enable the study of quantum measurements and experiments from the perspective of computational complexity and communication complexity. The measurement process is described, in its utmost generality, by a many-round quantum interaction
protocol between the experimental system and a full-fledged quantum computer. The QUALM complexity is quantified by the number of elementary operations performed by the quantum computer, including its coupling to the experimental system. We study how the QUALM complexity depends on the type of allowed access the quantum computer has to the experimental system: coherent, incoherent, etc. We provide a new example of a measurement "task", which can be motivated by the study of Floquet
systems, for which the coherent access QUALM complexity is exponentially better than the incoherent one, even if the latter is adaptive; this implies that using entanglement between different systems in experiments, as well as coherence between probes to the physical system at different times, may lead to exponential savings in resources. We extend our results to derive a similar exponential advantage for another physically motivated measurement task which determines the symmetry class of the time evolution operator for a quantum many-body system.


Please contact Subharee Patro or Jop Briet for the zoom link.

N&O Seminar: Simon Telen (MPI Leipzig)

  • 2021-03-17T14:00:00+01:00
  • 2021-03-17T15:00:00+01:00
March 17 Wednesday

Start: 2021-03-17 14:00:00+01:00 End: 2021-03-17 15:00:00+01:00

Everyone is welcome to attend the online N&O seminar with Simon Telen (MPI Leipzig). Title: Eigenvalue methods for solving polynomial systems.

Abstract:
The problem of computing the isolated solutions to a system of polynomial equations can be translated into an eigenvalue problem. Standard methods for performing this translation, such as Groebner basis algorithms, may lead to a drastic amplification of rounding errors. This renders the approach unfeasible for floating point computations. In this talk I will discuss two important remedies. On the one hand, it is crucial to make a good choice for the basis of the coordinate ring of the finite solution set. Secondly, working in an appropriate, compact space allows us to deal with ‘solutions at infinity’ in a robust manner. This leads to interesting questions related to the regularity of homogeneous ideals in Cox rings. I will show that, although classical methods fail at intersecting two degree 15 plane curves, we can accurately compute the 28900 intersection points of two degree 170 curves using these new techniques.


Please contact Daniel Dadush for the zoom link.

PhD Defense Stef Maree

  • 2021-03-17T14:00:00+01:00
  • 2021-03-17T15:00:00+01:00
March 17 Wednesday

Start: 2021-03-17 14:00:00+01:00 End: 2021-03-17 15:00:00+01:00

University of Amsterdam

Everyone is invited to attend the public defense of Stef of his PhD thesis:

Model-based evolutionary algorithms for finding diverse high-quality solutions - with an application in brachytherapy for prostate cancer

Promotor 1: Prof.dr. Peter A.N. Bosman, CWI, Amsterdam / TU Delft

Promotor 2: Prof.dr. C.R.N. Rasch, AMC / UvA

Copromotor 1: Dr. Tanja Alderliesten, LUMC, Leiden / UvA

Copromotor 2: Dr. A. Bel, AMC / UvA

 

 Link on YouTube: https://www.youtube.com/watch?v=Va0yCngtHnI

QuSoft Seminar: Nikhil Mande (QuSoft, CWI)

  • 2021-03-12T11:00:00+01:00
  • 2021-03-12T12:00:00+01:00
March 12 Friday

Start: 2021-03-12 11:00:00+01:00 End: 2021-03-12 12:00:00+01:00

Everyone is welcome to attend the online QuSoft seminar, this week with Nikhil Mande (QuSoft, CWI) on 'Symmetry and Quantum Query-to-Communication Simulation'.

Abstract: Buhrman, Cleve and Wigderson (STOC'98) showed that for every Boolean function f : {-1,1}^n to {-1,1} and G in {AND_2, XOR_2}, the bounded-error quantum communication complexity of the composed function f o G equals O(Q(f) log n), where Q(f) denotes the bounded-error quantum query complexity of f.
This is achieved by Alice running the optimal quantum query algorithm for f, using a round of O(log n) qubits of communication to implement each query.
This is in contrast with the classical setting, where it is easy to show that R^{cc}(f o G) < 2 R(f), where R^{cc} and R denote bounded-error communication and query complexity, respectively. Chakraborty et al. (CCC'20) exhibited a total function for which the log n overhead in the BCW simulation is required. We improve upon their result in several ways.

1) We show that the log n overhead is *not* required when f is symmetric (i.e., depends only on the Hamming weight of its input), generalizing a result of Aaronson and Ambainis for the Set-Disjointness function (Theory of Computing'05). This upper bound assumes a shared entangled state, though for most symmetric functions the assumed number of entangled qubits is less than the communication and hence could be part of the communication. In order to prove this, we design an efficient distributed version of noisy amplitude amplification that allows us to prove the result when f is the OR function.

2) In view of our first result above, one may ask whether the log n overhead in the BCW simulation can be avoided even when f is transitive-symmetric, which is a weaker notion of symmetry. We give a strong negative answer by showing that the log n overhead is still necessary for some transitive-symmetric functions even when we allow the quantum communication protocol an error probability that can be arbitrarily close to 1/2 (this corresponds to the unbounded-error model of communication).

Based on joint work with Sourav Chakraborty, Arkadev Chattopadhyay, Peter Høyer, Manaswi Paraashar, and Ronald de Wolf (https://arxiv.org/abs/2012.05233)


Please contact Subhasree Patro or Jop Briet for the zoomlink.

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