@article{40381,
  abstract     = {{<jats:title>Abstract</jats:title>
               <jats:p>The phenomenon of entanglement is the basis of quantum information and quantum communication processes. Entangled systems with a large number of photons are of great interest at present because they provide a platform for streaming technologies based on photonics. In this paper we present a device which operates with four-photons and based on the Hong–Ou–Mandel interference. The presented device allows to maximize the degree of spatial entanglement and generate the highly entangled four-dimensional Bell states. Furthermore, the use of the interferometer in different regimes leads to fast interference fringes in the coincidence probability with period of oscillations twice smaller than the pump wavelength. We have a good agreement between theoretical simulations and experimental results.</jats:p>}},
  author       = {{Ferreri, A and Ansari, V and Brecht, Benjamin and Silberhorn, Christine and Sharapova, Polina R.}},
  issn         = {{2058-9565}},
  journal      = {{Quantum Science and Technology}},
  keywords     = {{Electrical and Electronic Engineering, Physics and Astronomy (miscellaneous), Materials Science (miscellaneous), Atomic and Molecular Physics, and Optics}},
  number       = {{4}},
  publisher    = {{IOP Publishing}},
  title        = {{{Spatial entanglement and state engineering via four-photon Hong–Ou–Mandel interference}}},
  doi          = {{10.1088/2058-9565/abb411}},
  volume       = {{5}},
  year         = {{2020}},
}

@article{14544,
  author       = {{Vondran, J. and Spitzer, F. and Bayer, M. and Akimov, I. A. and Trautmann, Alexander and Reichelt, Matthias and Meier, Cedrik and Weber, N. and Meier, Torsten and André, R. and Mariette, H.}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{15}},
  pages        = {{155308}},
  title        = {{{Spatially asymmetric transients of propagating exciton-polariton modes in a planar CdZnTe/CdMgTe guiding structure}}},
  doi          = {{10.1103/physrevb.100.155308}},
  volume       = {{100}},
  year         = {{2019}},
}

@article{10014,
  abstract     = {{The cubic, tetragonal, and orthorhombic phase of potassium niobate (KNbO3) are studied based on density-functional theory. Starting from the relaxed atomic geometries, we analyze the influence of self-energy corrections on the electronic band structure within the GW approximation. We find that quasiparticle shifts widen the direct (indirect) band gap by 1.21 (1.44), 1.58 (1.55), and 1.67 (1.64) eV for the cubic, tetragonal, and orthorhombic phase, respectively. By solving the Bethe-Salpeter equation, we obtain the linear dielectric function with excitonic and local-field effects, which turn out to be essential for good agreement with experimental data. From our results, we extract an exciton binding energy of 0.6, 0.5, and 0.5 eV for the cubic, tetragonal, and orthorhombic phase, respectively. Furthermore, we investigate the nonlinear second-harmonic generation (SHG) both theoretically and experimentally. The frequency-dependent second-order polarization tensor of orthorhombic KNbO3 is measured for incoming photon energies between 1.2 and 1.6 eV. In addition, calculations within the independent-(quasi)particle approximation are performed for the tetragonal and orthorhombic phase. The novel experimental data are in excellent agreement with the quasiparticle calculations and resolve persistent discrepancies between earlier experimental measurements and ab initio results reported in the literature.}},
  author       = {{Schmidt, Falko and Riefer, Arthur and Schmidt, Wolf Gero and Schindlmayr, Arno and Imlau, Mirco and Dobener, Florian and Mengel, Nils and Chatterjee, Sangam and Sanna, Simone}},
  issn         = {{2475-9953}},
  journal      = {{Physical Review Materials}},
  number       = {{5}},
  publisher    = {{American Physical Society}},
  title        = {{{Quasiparticle and excitonic effects in the optical response of KNbO3}}},
  doi          = {{10.1103/PhysRevMaterials.3.054401}},
  volume       = {{3}},
  year         = {{2019}},
}

@article{29746,
  author       = {{Nicholson, C. W. and Puppin, M. and Lücke, A. and Gerstmann, Uwe and Krenz, Marvin and Schmidt, Wolf Gero and Rettig, L. and Ernstorfer, R. and Wolf, M.}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{15}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Excited-state band mapping and momentum-resolved ultrafast population dynamics in In/Si(111) nanowires investigated with XUV-based time- and angle-resolved photoemission spectroscopy}}},
  doi          = {{10.1103/physrevb.99.155107}},
  volume       = {{99}},
  year         = {{2019}},
}

@article{10015,
  author       = {{Dues, Christof and Schmidt, Wolf Gero and Sanna, Simone}},
  issn         = {{2470-1343}},
  journal      = {{ACS Omega}},
  pages        = {{3850--3859}},
  title        = {{{Water Splitting Reaction at Polar Lithium Niobate Surfaces}}},
  doi          = {{10.1021/acsomega.8b03271}},
  year         = {{2019}},
}

@article{26296,
  author       = {{Sperling, Jan and Perez-Leija, Armando and Busch, Kurt and Silberhorn, Christine}},
  issn         = {{2469-9926}},
  journal      = {{Physical Review A}},
  title        = {{{Mode-independent quantum entanglement for light}}},
  doi          = {{10.1103/physreva.100.062129}},
  year         = {{2019}},
}

@article{37288,
  abstract     = {{<jats:p>An integrated chip with quantum state generation, active polarization manipulation, and precise time control is demonstrated.</jats:p>}},
  author       = {{Luo, Kai-Hong and Brauner, Sebastian and Eigner, Christof and Sharapova, Polina and Ricken, Raimund and Meier, Torsten and Herrmann, Harald and Silberhorn, Christine}},
  issn         = {{2375-2548}},
  journal      = {{Science Advances}},
  keywords     = {{Multidisciplinary}},
  number       = {{1}},
  publisher    = {{American Association for the Advancement of Science (AAAS)}},
  title        = {{{Nonlinear integrated quantum electro-optic circuits}}},
  doi          = {{10.1126/sciadv.aat1451}},
  volume       = {{5}},
  year         = {{2019}},
}

@inproceedings{13285,
  author       = {{Hannes, Wolf-Rüdiger and Krauß-Kodytek, Laura and Ruppert, Claudia and Betz, Markus and Meier, Torsten}},
  booktitle    = {{Ultrafast Phenomena and Nanophotonics XXIII}},
  editor       = {{Betz, Markus and Elezzabi, Abdulhakem Y.}},
  isbn         = {{9781510624740}},
  title        = {{{Intensity-dependent degenerate and non-degenerate nonlinear optical absorption of direct-gap semiconductors}}},
  doi          = {{10.1117/12.2503539}},
  volume       = {{10916}},
  year         = {{2019}},
}

@article{13284,
  author       = {{Hannes, Wolf-Rüdiger and Meier, Torsten}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{12}},
  title        = {{{Higher-order contributions and nonperturbative effects in the nondegenerate nonlinear optical absorption of semiconductors using a two-band model}}},
  doi          = {{10.1103/physrevb.99.125301}},
  volume       = {{99}},
  year         = {{2019}},
}

@article{13365,
  abstract     = {{The KTiOPO4 (KTP) band structure and dielectric function are calculated on various levels of theory starting from density-functional calculations. Within the independent-particle approximation an electronic transport gap of 2.97 eV is obtained that widens to about 5.23 eV when quasiparticle effects are included using the GW approximation. The optical response is shown to be strongly anisotropic due to (i) the slight asymmetry of the TiO6 octahedra in the (001) plane and (ii) their anisotropic distribution along the [001] and [100] directions. In addition, excitonic effects are very important: The solution of the Bethe–Salpeter equation indicates exciton binding energies of the order of 1.5 eV. Calculations that include both quasiparticle and excitonic effects are in good agreement with the measured reflectivity.}},
  author       = {{Neufeld, Sergej and Bocchini, Adriana and Gerstmann, Uwe and Schindlmayr, Arno and Schmidt, Wolf Gero}},
  issn         = {{2515-7639}},
  journal      = {{Journal of Physics: Materials}},
  pages        = {{045003}},
  publisher    = {{IOP Publishing}},
  title        = {{{Potassium titanyl phosphate (KTP) quasiparticle energies and optical response}}},
  doi          = {{10.1088/2515-7639/ab29ba}},
  volume       = {{2}},
  year         = {{2019}},
}

@article{26300,
  author       = {{Sperling, Jan and Meyer-Scott, E. and Barkhofen, Sonja and Brecht, Benjamin and Silberhorn, Christine}},
  issn         = {{0031-9007}},
  journal      = {{Physical Review Letters}},
  title        = {{{Experimental Reconstruction of Entanglement Quasiprobabilities}}},
  doi          = {{10.1103/physrevlett.122.053602}},
  year         = {{2019}},
}

@inproceedings{43748,
  abstract     = {{The fundamental interband absorption in gallium arsenide shows a strong blue shift when biased by mid-infrared transients exceeding 10 MV/cm. This subcycle feature is induced by the localization of electronic wavefunctions from 3D to 2D.}},
  author       = {{Meier, Torsten and Bühler, Johannes and Schmidt, Christian and Heinrich, Alexander-Cornelius and Allerbeck, Jonas and Podzimski, Reinold and Berghoff, Daniel and Schmidt, Wolf Gero and Reichl, Christian and Wegscheider, Werner and Brida, Daniele and Leitenstorfer, Alfred}},
  booktitle    = {{XXI International Conference on Ultrafast Phenomena 2018 (UP 2018)}},
  publisher    = {{EDP Sciences}},
  title        = {{{Subcycle Wannier-Stark Localization by Mid-Infrared Bias in Gallium Arsenide}}},
  doi          = {{10.1051/epjconf/201920505001}},
  volume       = {{205}},
  year         = {{2019}},
}

@article{22887,
  author       = {{Vondran, J. and Spitzer, F. and Bayer, M. and Akimov, I. A. and Trautmann, Alexander and Reichelt, Matthias and Meier, Cedrik and Weber, N. and Meier, Torsten and André, R. and Mariette, H.}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{15}},
  pages        = {{155308}},
  title        = {{{Spatially asymmetric transients of propagating exciton-polariton modes in a planar CdZnTe/CdMgTe guiding structure}}},
  doi          = {{10.1103/physrevb.100.155308}},
  volume       = {{100}},
  year         = {{2019}},
}

@unpublished{22884,
  abstract     = {{Measurement-induced nonclassical effects in a two-mode interferometer are
investigated theoretically using numerical simulations and analytical results.
We demonstrate that for certain parameters measurements within the
interferometer lead to the occurrence of two-mode squeezing. The results
strongly depend on the detection probability, the phase inside the
interferometer, and the choice of the input states. The appropriate parameters
for maximized squeezing are obtained. We analyze the influence of losses and
confirm that the predicted effects are within reach of current experimental
techniques.}},
  author       = {{Riabinin, Matvei and Sharapova, Polina and Bartley, Tim and Meier, Torsten}},
  booktitle    = {{arXiv:1912.09097}},
  title        = {{{Generating two-mode squeezing with multimode measurement-induced nonlinearity}}},
  year         = {{2019}},
}

@article{13900,
  author       = {{Song, Xiaohong and Zuo, Ruixin and Yang, Shidong and Li, Pengcheng and Meier, Torsten and Yang, Weifeng}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  number       = {{3}},
  pages        = {{2225--2234}},
  title        = {{{Attosecond temporal confinement of interband excitation by intraband motion}}},
  doi          = {{10.1364/oe.27.002225}},
  volume       = {{27}},
  year         = {{2019}},
}

@article{13283,
  author       = {{Duc, Huynh Thanh and Ngo, Cong and Meier, Torsten}},
  issn         = {{2469-9950}},
  journal      = {{Physical Review B}},
  number       = {{4}},
  title        = {{{Ballistic photocurrents in semiconductor quantum wells caused by the excitation of asymmetric excitons}}},
  doi          = {{10.1103/physrevb.100.045308}},
  volume       = {{100}},
  year         = {{2019}},
}

@article{13429,
  author       = {{Bocchini, Adriana and Neufeld, Sergej and Gerstmann, Uwe and Schmidt, Wolf Gero}},
  issn         = {{0953-8984}},
  journal      = {{Journal of Physics: Condensed Matter}},
  pages        = {{385401}},
  title        = {{{Oxygen and potassium vacancies in KTP calculated from first principles}}},
  doi          = {{10.1088/1361-648x/ab295c}},
  volume       = {{31}},
  year         = {{2019}},
}

@article{20578,
  author       = {{Driben, R and Ma, Xuekai and Schumacher, Stefan and Meier, Torsten}},
  issn         = {{0146-9592}},
  journal      = {{Optics Letters}},
  number       = {{6}},
  pages        = {{1327--1330}},
  title        = {{{Bloch oscillations of multidimensional dark soliton wave packets and light bullets}}},
  doi          = {{10.1364/ol.44.001327}},
  volume       = {{44}},
  year         = {{2019}},
}

@article{15851,
  author       = {{Ma, Xuekai and Kartashov, Yaroslav Y and Gao, Tingge and Schumacher, Stefan}},
  issn         = {{1367-2630}},
  journal      = {{New Journal of Physics}},
  title        = {{{Controllable high-speed polariton waves in a PT-symmetric lattice}}},
  doi          = {{10.1088/1367-2630/ab5a9b}},
  volume       = {{21}},
  year         = {{2019}},
}

@unpublished{13340,
  abstract     = {{Spontaneous formation of transverse patterns is ubiquitous in nonlinear
dynamical systems of all kinds. An aspect of particular interest is the active
control of such patterns. In nonlinear optical systems this can be used for
all-optical switching with transistor-like performance, for example realized
with polaritons in a planar quantum-well semiconductor microcavity. Here we
focus on a specific configuration which takes advantage of the intricate
polarization dependencies in the interacting optically driven polariton system.
Besides detailed numerical simulations of the coupled light-field exciton
dynamics, in the present paper we focus on the derivation of a simplified
population competition model giving detailed insight into the underlying
mechanisms from a nonlinear dynamical systems perspective. We show that such a
model takes the form of a generalized Lotka-Volterra system for two competing
populations explicitly including a source term that enables external control.
We present a comprehensive analysis both of the existence and stability of
stationary states in the parameter space spanned by spatial anisotropy and
external control strength. We also construct phase boundaries in non-trivial
regions and characterize emerging bifurcations. The population competition
model reproduces all key features of the switching observed in full numerical
simulations of the rather complex semiconductor system and at the same time is
simple enough for a fully analytical understanding of the system dynamics.}},
  author       = {{Pukrop, Matthias and Schumacher, Stefan}},
  booktitle    = {{arXiv:1903.12534}},
  title        = {{{Externally Controlled Lotka-Volterra Dynamics in a Linearly Polarized  Polariton Fluid}}},
  year         = {{2019}},
}