Joint Seminar on Quantum Information and Technologies
2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025 | YouTube channel
until 2023/2024 Quantum Information Seminar | YouTube channel
2019-11-14 (Thursday)
room 1.03, Pasteura 5 at 11:15 
Alex Streltsov (Centre for Quantum Optical Technologies, UW)Rates of multi-partite entanglement transformations and applications in quantum networks
The theory of the asymptotic manipulation of pure bipartite quantumsystems can be considered completely understood: The rates at whichbipartite entangled states can be asymptotically transformed intoeach other are fully determined by a single number each, the respectiveentanglement entropy. In the multi-partite setting, similar questionsof the optimally achievable rates of transforming one pure state intoanother are notoriously open. This seems particularly unfortunatein the light of the revived interest in such questions due to theperspective of experimentally realizing multi-partite quantum networks.In this work, we report substantial progress by deriving surprisinglysimple upper and lower bounds on the rates that can be achieved inasymptotic multi-partite entanglement transformations. These boundsare based on ideas of entanglement combing and state merging. We identify cases where the bounds coincide and hence provide the exact rates. As an example, we bound rates at which resource states for the cryptographic scheme of quantum secret sharing can be distilled from arbitrary pure tripartite quantum states, providing further scope for quantum internet applications beyond point-to-point.
2019-11-07 (Thursday)
room 1.03, Pasteura 5 at 11:15
Kangda Wu (University of Science and Technology, Hefei, China)Realization of Generalized Quantum Measurement Based on Linear Optics
Quantum measurements are the key for extracting information from quantum systems and for connecting the quantum world with the classical world. Understanding the power and limitation of measurements is of paramount importance not only to foundational studies, but also to many applications, such as quantum tomography, metrology, and communication. However, demonstrating the generalized measurement on single-qubit system and multi-qubit systems in experiments has is a daunting task. Here, we report the very recent results in our group which have demonstrated the advantage of generalized collective measurement on different tasks, e.g, state tomography, parameter estimation and back-action reduction.
2019-10-24 (Thursday)
room 1.03, Pasteura 5 at 11:15
Robert Keil (Department of Experimental Physics, University of Innsbruck, Austria)Testing the foundations of quantum mechanics with multi-path interferometers
Quantum mechanics in its modern formulation relies on several fundamental axioms. One of these axioms is that states of a system are represented by complex wavefunctions. Another, the Born rule, relates these wavefunction to measurable probabilities by stating that the probability density equates the squared magnitude of the wavefunction. Interestingly, both axioms can be tested against potential generalisations by one and the same experiment in a multi-path interferometer. In this talk, I will give an introduction into the field, present the state of the art and our latest results in this direction, which have been obtained with both, free space and integrated waveguide interferometers.
2019-10-17 (Thursday)
room 1.03, Pasteura 5 at 11:15
Sreetama Das (IFT UW)Quantum Information Processing in Noisy Environments
We will discuss various quantum informatic aspects of a system,when it is interacting with an environment and the effects of disorder on the system induced by the environment. In the first part, we will identify a set of dynamical maps of open quantum system, and refer to them as “epsilon-Markovian” maps. It is constituted of maps that possibly violate Markovianity but only a “little". We will analytically derive a bound on the epsilon-nonmarkovianity of a dynamical map, in terms of an entanglement-like resource generated between the system and its “immediate” environment.We will next show that one can construct a quantum absorption refrigeratorthat provides refrigeration only in the transient regime, by using threeinteracting qubits, each of which is also interacting with its own localheat-bath. The machine either does not provide cooling in the steadystate, or the steady state is achieved after a long time.If time permits, we will discuss a freezing effect of quenched disorder ina Hubbard model and a localization-like phenomenon due to a similardisorder in a quantum random walk.References:Almost Markovian maps and entanglement-based bound on correspondingnon-Markovianity, arXiv:1905.06198.Necessarily transient quantum refrigerator, arXiv:1606.06985.Adiabatic freezing of entanglement with insertion of defects inone-dimensional Hubbard model, arXiv:1708.07005.Inhibition of spreading in quantum random walks due to quenchedPoisson-distributed disorder, arXiv:1806.04024.
2019-10-10 (Thursday)
room 1.03, Pasteura 5 at 11:15
Marcin Jarzyna (CeNT UW)Ultimate capacity limits for fiber links with phase insensitive amplification
2019-10-03 (Thursday)
room 1.03, Pasteura 5 at 11:15
Raul Garcia-Patron Sanchez (Université libre de Bruxelles)The effect of noise in quantum supremacy demonstrations
The recent leakage of a paper claiming an experimental demonstration of quantum computational supremacy by a team of researcher from Google has been on the news very recently. In this talk we will discuss the most important potential loophole of any quantum supremacy proposals, the possibility that a classical algorithm exploits the natural noise in a real quantum supremacy demonstration to turn an initial intractable problem into an easier one. We will show how this is possible for boson sampling, a quantum supremacy proposal based on quantum photonics technology and discuss its potential implications for the leaked experiment by Google.