START Fellow 2019

Ludwig-Maximilians-Universität München, Max Planck Institute of Quantum Optics

Research website

Research in quantum physics allows in a unique way musing about fundamental questions regarding the nature of physical entities, while at the same time promises the development of groundbreaking applications in many distinct areas ranging from computer science and communication technology to precision measurements and simulations in biology and chemistry.


I am interested in developing entanglement detection schemes and implementing different quantum measurement schemes.

The main objective my START project is to develop integrated waveguides as a tool for simulations of open quantum systems. I have been working with integrated photonics for many years, however, open quantum systems are a new topic and thus I am quite excited to learn more about this field and make it accessible to the integrated photonics platform.

Featured on the Research in Bavaria website: Supporting independence in quantum research

Website: https://xqp.physik.uni-muenchen.de/


Cooperation and dependencies in multipartite systems

W. Kłobus, M. Miller, M. Pandit, R.Ganardi, L. Knips, J. Dziewior, J. Meinecke, H. Weinfurter, W. Laskowski, T. Paterek

NJP 23, 63057 (2021).

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We propose an information-theoretic quantifier for the advantage gained from cooperation that captures the degree of dependency between subsystems of a global system. The quantifier is distinct from measures of multipartite correlations despite sharing many properties with them. It is directly computable for classical as well as quantum systems and reduces to comparing the respective conditional mutual information between any two subsystems. Exemplarily we show the benefits of using the new quantifier for symmetric quantum secret sharing. We also prove an inequality characterizing the lack of monotonicity of conditional mutual information under local operations and provide intuitive understanding for it. This underlines the distinction between the multipartite dependence measure introduced here and multipartite correlations.

DOI: 10.1088/1367-2630/abfb89

Implementing graph-theoretic quantum algorithms on a silicon photonic quantum walk processor

X.G. Qiang, Y.Z. Wang, S.C. Xue, R.Y. Ge, L.F. Chen, Y.W. Liu, A.Q. Huang, X. Fu, P. Xu, T. Yi, F.F. Xu, M.T. Deng, J.B. Wang, J.D.A. Meinecke, J.C.F. Matthews, X.L. Cai, X.J. Yang, J.J. Wu

Science Advances 7 (9), eabb8375 (2021).

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Applications of quantum walks can depend on the number, exchange symmetry and indistinguishability of the particles involved, and the underlying graph structures where they move. Here, we show that silicon photonics, by exploiting an entanglement-driven scheme, can realize quantum walks with full control over all these properties in one device. The device we realize implements entangled two-photon quantum walks on any five-vertex graph, with continuously tunable particle exchange symmetry and indistinguishability. We show how this simulates single-particle walks on larger graphs, with size and geometry controlled by tuning the properties of the composite quantum walkers. We apply the device to quantum walk algorithms for searching vertices in graphs and testing for graph isomorphisms. In doing so, we implement up to 100 sampled time steps of quantum walk evolution on each of 292 different graphs. This opens the way to large-scale, programmable quantum walk processors for classically intractable applications.

DOI: 10.1126/sciadv.abb8375

Multipartite entanglement analysis from random correlations

L. Knips, J. Dziewior, W. Klobus, W. Laskowski, T. Paterek, P.J. Shadbolt, H. Weinfurter, J.D.A. Meinecke

NPJ Quantum Information 6 (1), 51 (2020).

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Quantum entanglement is usually revealed via a well aligned, carefully chosen set of measurements. Yet, under a number of experimental conditions, for example in communication within multiparty quantum networks, noise along the channels or fluctuating orientations of reference frames may ruin the quality of the distributed states. Here, we show that even for strong fluctuations one can still gain detailed information about the state and its entanglement using random measurements. Correlations between all or subsets of the measurement outcomes and especially their distributions provide information about the entanglement structure of a state. We analytically derive an entanglement criterion for two-qubit states and provide strong numerical evidence for witnessing genuine multipartite entanglement of three and four qubits. Our methods take the purity of the states into account and are based on only the second moments of measured correlations. Extended features of this theory are demonstrated experimentally with four photonic qubits. As long as the rate of entanglement generation is sufficiently high compared to the speed of the fluctuations, this method overcomes any type and strength of localized unitary noise.

DOI: 10.1038/s41534-020-0281-5

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