Nguyễn Hải Châu

Postdoctoral researcher
Room: 2B3
Phone: +49 (0) 351 871-2203
Email: chau@pks.mpg.de

Research interest

Since September 2015 I work at the Max Planck Institute for the Physics of Complex Systems (Dresden) as a postdoctoral researcher. I am attracted to the foundational questions at the interface of information theory, quantum mechanics and the theory of relativity. Currently, my main works concentrate on studying quantum nonlocality. The other question that I enjoy thinking about most of the time is the relativistic formulation of quantum information theory.

Before coming to Dresden, I have worked on several different topics linked to statistical physics, inference and quantum theory. I studied the statistical physics of inference problems with applications in cancer research during my Ph.D. with Prof. Johannes Berg in the Institute for Theoretical Physics, University of Cologne (Cologne, Germany). I also enjoyed studying the quasi-relativistic physics of graphene with Prof. V. Lien Nguyen in Hanoi Institute of Physics (Hanoi, Vietnam), and then with Prof. Markus Müller in the International Center for Theoretical Physics (Trieste, Italy).

Publications

Quantum nonlocality

  • H. Chau Nguyen, Antony Milne, Thanh Vu and Sania Jevtic, "Quantum steering with positive operator valued measures", arXiv:1706.08166 (2017). After quite some time tried and failed, I find very relieved that we are finally able to construct a general approach to study quantum steering with POVMs. As the first application, we use it to show a numerical evidence that POVMs and PVMs are actually equivalent in steering Werner states and T-states (see also IQI open quantum problems). Don't be disappointed; I hope that they are not equivalent in other situations!
  • H. Chau Nguyen and Kimmo Luoma, "On the pure state outcomes of Einstein-Podolsky-Rosen steering", Phys. Rev. A 95 042117 (2017). Using the purification technique, we show that pure steering outcomes often carry interesting information about the shared state. As an application, we generalise the fundamental lemma in the so-called `all-versus-nothing proof of steerability' for systems of arbitrary dimension.
  • H. Chau Nguyen and Thanh Vu, "Necessary and sufficient condition for steerability of two-qubit states by the geometry of steering outcomes", Europhys. Lett. 115 10003 (2016). We derive a necessary and sufficient condition for steerability of two-qubit states, and thereby prove a very interesting conjecture on the steerability of the so-called two-qubit T-states.
  • H. Chau Nguyen and Thanh Vu, "Non-separability and steerability of two-qubit states from the geometry of steering outcomes", Phys. Rev. A 94 012114 (2016). We show that the problem of classification of two-qubit states into nonseparable and steerable classes can be understood as a geometrical problem of classifying the so-called double-cones of steering outcomes in the 4D Euclidean space.

Graphene: an effective relativistic system

  • H. Chau Nguyen, Nhung T. T. Nguyen and V. Lien Nguyen, "On the density of states of circular graphene quantum dots", arXiv:1706.08166 (2017). We suggest a simple, fast and easy method to calculate the LDOS of graphene quantum dots, which avoid the computation by indirectly by the scattering coefficient method and by the finite difference method.
  • H. Chau Nguyen, Nhung T. T. Nguyen and V. Lien Nguyen, "The transfer matrix approach to circular graphene quantum dots", J. Phys.: Condens. Matter 28 275301 (2016). This work unifies the calculations of bound states, quasi-bound states and scattering cross-sections of a circular graphene quantum dot in a single framework.
  • Markus Müller and H. Chau Nguyen, "Collision-dominated spin transport in graphene and Fermi liquids", New J. Phys. 13 035009 (2011) . The collision-dominated spin transport in graphene and Fermi liquids is studied. An exact relation of spin conductance of pristine graphene with its electronic conductance is established.
  • C. Huy Pham, H. Chau Nguyen, V. Lien Nguyen, "Massless Dirac fermions in a graphene superlattice: a T-matrix approach", J. Phys.: Condens. Matter 22 425501 (2010) . Peculiar properties of Dirac fermions in superlattice are derived in a simple manner.
  • H. Chau Nguyen and V. Lien Nguyen, "Tunneling of Dirac electrons through one-dimensional potentials in graphene: a T-matrix approach", J. Phys.: Condens. Matter 21 045305 (2009) . A simple method to calculate the conductance of an arbitrary one-dimensional conjunction potential in graphene is formulated.
  • H. Chau Nguyen, M.Tien Hoang and V. Lien Nguyen, "Quasi-bound states induced by one-dimensional potentials in graphene", Phys. Rev. B 79 035411 (2009). Here the problem of finding quasi-bound states is made an easy exercise by the transfer matrix method.

Statistical inference, information and data mining

  • H. Chau Nguyen, Riccardo Zecchina and Johannes Berg "Inverse statistical problems: from the inverse Ising problem to data science", Advances in Physics (2017). We review some applications and theoretical understanding of the inverse Ising problem. The connection between maximum likelihood inference and thermodynamics is emphasised. Methods of inference in the low sampling regime (pseudolikelihood, interaction screening) are also discussed.
  • Simon L. Dettmer, H. Chau Nguyen and Johannes Berg, "Network inference in the non-equilibrium steady state", Phys. Rev. E 94, 052116 (2016). We show that it is possible (!) to reconstruct the parameters of the dynamical Ising model based on sampled data of the (nonequilibrium) stationary state.
  • H. Chau Nguyen in Seidel et. al., "A genomics-based classification of human lung tumors", Science Transl. Med. 5(29) 209ra153 (2013). We devise a very simple semi-supervised classification method and apply the method to the classification of lung cancers.
  • H. Chau Nguyen and Johannes Berg, "Mean-field theory for the inverse Ising problem at low temperatures", Phys. Rev. Lett. 109 050602 (2012). Here the mystery of the failure of mean-field methods for the inverse Ising problem is explained.
  • H. Chau Nguyen and Johannes Berg, "Bethe-Peierls approximation and the inverse Ising problem", J. Stat. Mech. P03004 (2012). It is shown that Bethe-Peierls approximation allows for a simple solution to the inverse Ising problem, which is exact in tree.

Teaching

Theses

Other stuffs