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
2019-05-23 (Thursday)
room 1.03, Pasteura 5 at 11:15 
Katarzyna Roszak (Politechnika Wrocławska)Entanglement and objectivity in pure dephasing models
2019-05-16 (Thursday)
room 1.03, Pasteura 5 at 11:15
Paweł Kasprzak (KMMF UW)An Invitation to Compressed Sensing
The aim of this talk is to explain certain mathematical aspects of compressed sensing (CS) and describe a few classes of algorithms used by compressed sensing practitioners. Moreover the application of CS in Quantum Information as proposed by D. Gross et al. will be outlined. If time permits I will also describe applications of CS in NMR.
2019-05-09 (Thursday)
room 1.03, Pasteura 5 at 11:15
Julia Amaros Binefa (IQC, University of Waterloo)Field swept control in Electron Spin Resonance and k-space formalism
Pulsed electron spin resonance (ESR) is a technique that has found many applications in the fields of chemistry and biology. In order to enhance its sensitivity by several orders of magnitude, one can use on chip superconducting resonators with high quality factors. However, they also introduce new challenges because of their narrow bandwidth and nonlinear behavior. In this talk, I will describe our proposed solution to overcome these challenges in the context of measuring spectra, along with simulations and NMR measurements supporting its utility.In the second half of my talk, I will introduce the k-space formalism, a reciprocal space description often used in MRI. This method allows us to track the effect of evenly spaced pulses and a gradient drift hamiltonian on an ensemble of non-interacting spins. I will extend the existing description to incorporate the use of a frequency sweep, and demonstrate that it can be used in a continuum limit to understand the effect of any arbitrary control pulse.
2019-04-25 (Thursday)
room 1.03, Pasteura 5 at 11:15
Filip Maciejewski (IFT UW)Mitigation of measurement errors by classical post-processing based on Quantum Detector Tomography
Quantum devices in the near future will be inevitably noisy and imperfect. Hence it becomes an especially important task to develop error correction and mitigation schemes that would counter the destructive effects of noise and decoherence. The main aim of my talk is to present an error mitigation scheme for measurement (readout) errors of a particular, classical type. First, I will use the formalism of generalized quantum measurements (POVMs) to present a model of such noise. Second, I will show how to mitigate it using solely classical post-processing, provided one has access to knowledge about the noise. I will describe a procedure known as Quantum Detector Tomography, which allows to obtain such knowledge in practice. Furthermore, I will discuss the influence of finite statistics and possible deviations from the noise model, on the applicability of our procedure. Finally, I will present experimental results from IBM quantum devices, which confirm the effectiveness of our mitigation scheme for exemplary single and two-qubit experiments.
2019-04-11 (Thursday)
room 1.03, Pasteura 5 at 11:15
Amit Kumar Pal (IFT UW)Connecting robustness of entanglement with noise propagation
Entanglement is usually considered to be fragile against local noise. However, we show that situations can be found where entanglement remains constant over time in certain quantum many-body systems. We also connect the behaviour of entanglement with the propagation of noise via quantum many-body systems, in terms of the Lieb-Robinson's bound. Additionally, we point out certain interesting scale-invariant features of the behaviour of entanglement in specific quantum many-body systems.
2019-04-04 (Thursday)
room 1.03, Pasteura 5 at 11:15
Jan Kołodyński, Alexander Streltsov (Centre for Quantum Optical Technologies, UW)Entanglement negativity as a universal non-Markovianity witness
In order to engineer an open quantum system and its evolution, it is essential to identify and control the memory effects. These are formally attributed to the non-Markovianity of dynamics that manifests itself by the evolution being indivisible in time, a property which can be witnessed by a non-monotonic behavior of contractive functions or correlation measures. We show that by monitoring directly the entanglement behavior of a system in a tripartite setting it is possible to witness all invertible non-Markovian dynamics, as well as all (also non-invertible) qubit evolutions. This is achieved by using negativity, a computable measure of entanglement, which in the usual bipartite setting is not a universal non-Markovianity witness. We emphasize further the importance of multipartite states by showing that non-Markovianity cannot be faithfully witnessed by any contractive function of single qubits. We support our statements by an explicit example of eternally non-Markovian qubit dynamics, for which negativity can witness non-Markovianity at arbitrary time scales.
2019-03-28 (Thursday)
room 1.03, Pasteura 5 at 11:15
Karol Gietka (IFT UW)Quantum metrology beyond measurement
2019-03-21 (Thursday)
room 1.03, Pasteura 5 at 11:15
Jan Krzywda (IFT UW)Theory of coherent spin transfer between two silicon quantum dots
Recently experimentalists have been attempting to use theelectron spin as flying qubit in the silicon nanostructures, which haveestablished its position as the most promising platform for quantumcomputation. Not only will I describe why the latter is believed, but alsocarefully explain the electron shuttling in terms of everlasting Landau -Zener problem. Contrary to common believe this ubiquitous case ofadiabatic evolution and level crossing, here extended to the multiplelevels due to specific electronic structure of silicon, can be viewed fromvarious perspectives including: special function approach, quantuminformation theory, interferometry, noise spectroscopy or evenKibble-Żurek mechanism.Although my main task would be to show some of these interconnections andhence investigate how shuttling affects qubit coherence, as a side effectthe minute introduction to mostly unknown valley physics will be given.
2019-03-14 (Thursday)
room 1.03, Pasteura 5 at 11:15
Piotr Szańkowski (IFPAN)The dynamical-decoupling-based spatiotemporal noise spectroscopy
I will demonstrate how the standard, temporal-only, dynamical-decoupling-based noise spectroscopy method can be extended to also encompass the spatial degree of freedom. This spatiotemporal spectroscopy utilizes a system of multiple qubits arranged in a line that are undergoing pure dephasing due to environmental noise. When the qubits are driven by appropriately coordinated sequences of Pi-pulses the multi-qubit register becomes decoupled from all components of the noise, except for those characterized by frequencies and wavelengths specified by the pulse sequences. This allows for employment of the procedure for reconstruction of the two-dimensional spectral density that quantifies the power distribution among spatial and temporal harmonic components of the noise.
2019-03-07 (Thursday)