ORBi Collection: Physics
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Self broadening coefficients and improved line intensities for the n7 band of C2H4 near 10.5 mm, and impact on ethylene retrievals from Jungfraujoch solar spectra
http://hdl.handle.net/2268/170533
Title: Self broadening coefficients and improved line intensities for the n7 band of C2H4 near 10.5 mm, and impact on ethylene retrievals from Jungfraujoch solar spectra
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<br/>Author, co-author: Vander Auwera, Jean; Fayt, André; Tudorie, Marcela; Rotger - Languereau, Maud; Boudon, Vincent; Franco, Bruno; Mahieu, Emmanuel
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<br/>Abstract: Ethylene (ethene, C2H4) is a tropospheric pollutant on the Earth, also present as a by-product of methane photochemistry in the atmosphere of outer solar system bodies. Remote sensing of ethylene in the infrared range relies on the 10 mm region. This spectral range corresponds to the excitation of 7 modes of vibration of 12C2H4, 4 of which being infrared active (see Fig. 1 of [1]). The corresponding n10, n7, n4 and n12 bands are located near 826, 949, 1026 and 1442 cm-1, respectively [1]. Among these, the n7 band is the strongest, indeed used for remote sensing measurements of ethylene.
Relying on high-resolution Fourier transform infrared (FTIR) spectra recorded in Brussels, the present work involved extensive measurements of individual line intensities and self broadening coefficients for the n7 band of 12C2H4. Compared to the corresponding information available in the latest edition of the HITRAN spectroscopic database (HITRAN 2012 [2]), the measured line intensities were found to be higher by about 10 % for high J lines in the P branch and lower by about 5 % for high J lines of the R branch, varying between these two limits roughly linearly with the line positions. Test calculations performed in this work indicated that these discrepancies could result from the relative values of the transition moments of the n10, n7 and n12 bands used when the information provided in HITRAN was generated (the transition moment of the n4 band was set to zero). The measured self broadening coefficients exhibit a dependence on both J and Ka, which was modeled empirically. The spectroscopic information for ethylene available in HITRAN 2012 was modified to match the present observations. The impact of these modifications on retrievals of atmospheric ethylene was then evaluated via FTIR retrievals in the 949.0 – 952.0 cm-1 microwindow, from a subset of ground-based high-resolution FTIR solar spectra recorded at the Jungfraujoch station. The new line intensities were found to lead to a reduction of the measured total columns of ethylene by -4.1±0.1 %, compared to the use of HITRAN 2012.The origin of two-dimensional electron gases at oxide interfaces: insights from theory
http://hdl.handle.net/2268/170355
Title: The origin of two-dimensional electron gases at oxide interfaces: insights from theory
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<br/>Author, co-author: Bristowe, Nicholas; Ghosez, Philippe; Littlewood, P.B.; Artacho, E.
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<br/>Abstract: The response of oxide thin ﬁlms to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these ﬁndings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.Modeling reaction-limited Ostwald ripening of supported Ni catalysts in presence of CO: the role of particle size distribution
http://hdl.handle.net/2268/170353
Title: Modeling reaction-limited Ostwald ripening of supported Ni catalysts in presence of CO: the role of particle size distribution
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<br/>Author, co-author: Gommes, Cédric; Munnik, Peter; de Jongh, Petra; de Jong, KrijnDoping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission
http://hdl.handle.net/2268/170352
Title: Doping-dependent band structure of LaAlO3/SrTiO3 interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission
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<br/>Author, co-author: Cancellieri, C.; Reinle-Schmitt, M.L.; Kobayashi, M.; Strocov, V.N.; Willmott, P.R.; Fontaine, Denis; Ghosez, Philippe; Filippetti, A.; Delugas, P.; Fiorentini, V.
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<br/>Abstract: Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO3/SrTiO3 in a resonant angle-resolved photoemission experiment. A strong polarization dependence of the Fermi surface and band dispersions is demonstrated, highlighting different Ti 3d orbitals involved in two-dimensional (2D) conduction. Measurements on samples with different doping levels reveal different band occupancies and Fermi-surface areas.The photoemission results are directly compared with advanced ﬁrst-principles calculations, carried out for different 3d-band ﬁlling levels connected with the 2D mobile carrier concentrations obtained from transport measurements, with indication of charge localization at the interface.Linear electro-optic effect in multiferroic BiFeO3 thin ﬁlms
http://hdl.handle.net/2268/170351
Title: Linear electro-optic effect in multiferroic BiFeO3 thin ﬁlms
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<br/>Author, co-author: Sando, D.; Hermet, Patrick; Allibe, J.; Bourderionnet, J.; Fusil, S.; Carrétéro, C.; Jacquet, E.; Mage, J.-C.; Dolfi, D.; Barthélémy, A.; Ghosez, Philippe; Bibes, M.
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<br/>Abstract: Multiferroics are materials with coexisting magnetic and ferroelectric orders, which show potential for electrically controlled spintronic devices. A common application of ferroelectrics is in electro-optical modulators exploiting their electric-field-dependent optical indices. The coupling of optical and magnetic degrees of freedom is attractive for designing multifunctional devices, but to date the electro-optical response of multiferroics has hardly been explored. Here we report a joint experimental and theoretical study of this effect in multiferroic BiFeO3 thin ﬁlms. We conﬁrm the large birefringence present in single crystals and determine the electro-optic coefﬁcients r13 and r33. We present approaches to increase the obtained coefﬁcients, for instance, by using tetragonal-like BiFeO3, and expand the potential of multiferroics to optical applications.Self broadening coefficients and improved line intensities for the ν7 band of ethylene near 10.5 µm, and impact on ethylene retrievals from Jungfraujoch spectra
http://hdl.handle.net/2268/169909
Title: Self broadening coefficients and improved line intensities for the ν7 band of ethylene near 10.5 µm, and impact on ethylene retrievals from Jungfraujoch spectra
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<br/>Author, co-author: Vander Auwera, J; Fayt, A; Tudorie, M; Rotger, M; Boudon, V; Franco, Bruno; Mahieu, Emmanuel
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<br/>Abstract: Relying on high-resolution Fourier transform infrared (FTIR) spectra, the present work involved extensive measurements of individual line intensities and self broadening coefficients for the nu7 band of 12C2H4. The measured self broadening coefficients exhibit a dependence on both J and Ka. Compared to the corresponding information available in the latest edition of the HITRAN spectroscopic database, the measured line intensities were found to be higher by about 10 % for high J lines in the P branch and lower by about 5 % for high J lines of the R branch, varying between these two limits roughly linearly with the line positions. The impact of the presently measured line intensities on retrievals of atmospheric ethylene in the 949.0-952.0 cm-1 microwindow was evaluated using a subset of ground-based high-resolution FTIR solar spectra recorded at the Jungfraujoch station. The use of HITRAN 2012 with line intensities modified to match the present measurements led to a systematic reduction of the measured total columns of ethylene by -4.1+/-0.1 %.External constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
http://hdl.handle.net/2268/169737
Title: External constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
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<br/>Author, co-author: Sugny, Dominique; Vranckx, Stéphane; Ndong, Mamadou; Atabek, Osman; Desouter, MichèleExternal constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
http://hdl.handle.net/2268/169737
Title: External constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
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<br/>Author, co-author: Sugny, Dominique; Vranckx, Stéphane; Ndong, Mamadou; Atabek, Osman; Desouter, MichèleExternal constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
http://hdl.handle.net/2268/169737
Title: External constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
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<br/>Author, co-author: Sugny, Dominique; Vranckx, Stéphane; Ndong, Mamadou; Atabek, Osman; Desouter, MichèleExternal constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
http://hdl.handle.net/2268/169737
Title: External constraints on optical control strategies in molecular orientation and photofragmentation: role of zero-area fields
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<br/>Author, co-author: Sugny, Dominique; Vranckx, Stéphane; Ndong, Mamadou; Atabek, Osman; Desouter, MichèleThe two scenarios for quantum multifractality breakdown
http://hdl.handle.net/2268/169678
Title: The two scenarios for quantum multifractality breakdown
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<br/>Author, co-author: Georgeot, Bertrand; Dubertrand, Rémy; Garcia-Mata, Ignacio; Giraud, Olivier; Lemarié, Gabriel; Martin, John
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<br/>Abstract: Several types of physical systems are characterized by quantum wave func- tions with multifractal properties. In the quantum chaos field, they cor- respond to pseudointegrable systems, with properties intermediate between integrability and chaos. In condensed matter, they include electrons in a disordered potential at the Anderson metal-insulator transition. This multi- fractality leads to particular transport properties and appears in conjunction with specific types of spectral statistics. In parallel, progress in experimental techniques allows to observe finer and finer properties of the wavefunctions of quantum or wave systems, as well as to perform experiments with un- precedented control on the dynamics of the systems studied. In this context, this talk will discuss the robustness of multifractality in presence of footnote- size perturbations. We expose two scenarios for the breakdown of quantum multifractality under the effect of such perturbations. In the first scenario, multifractality survives below a certain scale of the quantum fluctuations. In the other one, the fluctuations of the wave functions are changed at every scale and each multifractal dimension smoothly goes to the ergodic value. We use as generic examples a one-dimensional dynamical system and the three- dimensional Anderson model at the metal-insulator transition, and show that for different types of perturbation the destruction of multifractal properties always follows one of these two ways. Our results thus suggest that quantum multifractality breakdown is universal and obeys one of these two scenarios depending on the perturbation. We also discuss the experimental implica- tions.Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal
http://hdl.handle.net/2268/169625
Title: Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal
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<br/>Author, co-author: Pękała, M.; Wolff-Fabris, F.; Fagnard, Jean-François; Vanderbemden, Philippe; Mucha, J.; Gospodinov, M. M.; Lovchinov, V.; Ausloos, Marcel
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<br/>Abstract: An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of a cubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6 T.Magnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0 to 0.2)
http://hdl.handle.net/2268/169622
Title: Magnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0 to 0.2)
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<br/>Author, co-author: Thaljaoui, R.; Boujelben, W.; Pękała, M.; Pękała, K.; Fagnard, Jean-François; Vanderbemden, Philippe; Donten, M.; Cheikhrouhou, A.
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<br/>Abstract: Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition.Magnetic susceptibility and electron magnetic resonance study of monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3
http://hdl.handle.net/2268/169619
Title: Magnetic susceptibility and electron magnetic resonance study of monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3
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<br/>Author, co-author: Thaljaoui, R.; Pękała, K.; Pękała, M.; Boujelben, W.; Szydłowska, J.; Fagnard, Jean-François; Vanderbemden, Philippe; Cheikhrouhou, A.
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<br/>Abstract: The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature.Structural, magnetic and magneto-transport properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3
http://hdl.handle.net/2268/169607
Title: Structural, magnetic and magneto-transport properties of monovalent doped manganite Pr0.55K0.05Sr0.4MnO3
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<br/>Author, co-author: Thaljaoui, R.; Boujelben, W.; Pękała, M.; Pękała, K.; Antonowicz, J.; Fagnard, Jean-François; Vanderbemden, Philippe; Dąbrowska, S.; Mucha, J.
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<br/>Abstract: Pr0.55K0.05Sr0.4MnO3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with Pnma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000–1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic–ferromagnetic transition at the Curie temperature TC = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg−1 K−1, resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013).Generation of artificial magnetic fields using dipole-dipole interactions
http://hdl.handle.net/2268/169604
Title: Generation of artificial magnetic fields using dipole-dipole interactions
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<br/>Author, co-author: Cesa, Alexandre; Martin, John
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<br/>Abstract: In 1996, Lloyd [1] showed that the dynamics of complex many-body quantum systems can be efficiently simulated by quantum computers, an idea first put forward by Manin [2] and further developed by Feynman [3]. Although the first quantum computers of a few qubits have been realised experimentally [4, 5], the advent of scalable quantum computers might take another few decades. An alternative tool in the context of simulation is a highly controllable quantum system able to mimic the dynamics of other complex quantum systems, known as an analog quantum simulator. Cold neutral atoms and trapped ions have been shown to be versatile quantum simulators [6, 7] thanks to their high flexibility, controllability, and scalability. They permit one to study a wide range of problems arising from atomic physics, relativistic quantum physics, or cosmology [8]. Since neutral atoms do not carry any net charge, the simulation of electric and magnetic condensed matter phenomena, such as the spin Hall effect, seems out of reach. To overcome this apparent difficulty, the idea has been proposed to create artificial electromagnetic potentials for neutral atoms based on atom-light interaction [9– 12]. These artificial potentials act on neutral atoms as real electromagnetic potentials act on charged particles. Many works on artificial gauge potentials induced by atom-light interactions adopt a single-particle approach [12]. The predicted potentials are then supposed to be valid for a system of weakly interacting atoms. So far, the consequences of atom-atom interactions on the generation of artificial gauge fields has little been studied. The aim of this work is to study the artificial gauge fields arising from the interaction of two Rydberg atoms driven by a common laser field [13]. In this situation, we show that the combined atom-atom and atom-field interactions give rise to nonuniform, artificial gauge potentials. We identify the mechanism responsible for the emergence of these gauge potentials. Analytical expressions for the latter indicate that the strongest artificial magnetic fields are reached in the regime intermediate between the dipole blockade regime and the regime in which the atoms are sufficiently far apart such that atom-light interaction dominates over atom-atom interactions. We discuss the differences and similarities of artificial gauge fields originating from resonant dipole-dipole [14] and van der Waals [15] interactions. We also give an estimation of experimentally attainable artificial magnetic fields resulting from this mechanism and we discuss their detection through the deflection of the atomic motion.
[1] S. Lloyd, Science 273, 1073 (1996).
[2] Yu. I. Manin, Computable and uncomputable, Sovetskoye Radio, Moscow, 1980.
[3] R. P. Feynman, Int. J. Theor. Phys. 21, 467 (1982).
[4] L. DiCarlo, J. M. Chow, J. M. Gambetta, Lev S. Bishop, B. R. Johnson, D. I. Schuster, J. Majer, A. Blais, L. Frunzio, S. M. Girvin, and R. J. Schoelkopf, Nature 460, 240 (2009). [5] N. Xu, J. Zhu, D. Lu, X. Zhou, X. Peng, and J. Du, Phys. Rev. Lett. 108, 130501 (2012).
[6] I. Buluta and F. Nori, Science 326, 108 (2009).
[7] I. Bloch, J. Dalibard and S. Nascimbéne, Nature Physics 8, 267 (2012).
[8] R. Blatt and C. F. Roos, Nature Physics 8, 277 (2012).
[9] G. Juzeliunas and P. Öhberg, Phys. Rev. Lett. 93, 033602 (2004).
[10] G. Juzeliunas, P. Öhberg, J. Ruseckas, and A. Klein, Phys. Rev. A 71, 053614 (2005).
[11] G. Juzeliunas, J. Ruseckas, P. Öhberg, and M. Fleischhauer, Phys. Rev. A 73, 025602 (2006).
[12] J. Dalibard, F. Gerbier, G. Juzeliu ̄nas, and P. Öhberg, Rev. Mod. Phys. 83, 1523 (2011).
[13] A. Cesa and J. Martin, Phys. Rev. A 88,062703 (2013). [14] A. Gaëtan, Y. Miroshnychenko, T. Wilk, A. Chotia, M. Viteau, D. Comparat, P. Pillet, A. Browaeys, and P. Grangier, Nature Physics 5, 115 (2009).
[15] L. Béguin, A. Vernier, R. Chicireanu, T. Lahaye, and A. Browaeys, Phys. Rev. Lett. 110, 263201 (2013).Alteration of decoherence-free states caused by dipole-dipole interactions
http://hdl.handle.net/2268/169599
Title: Alteration of decoherence-free states caused by dipole-dipole interactions
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<br/>Author, co-author: Damanet, François; Martin, John
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<br/>Abstract: Decoherence, known as the consequence of the coupling of any quantum system to its environment, causes information loss in the system and represents a major problem in the physical realization of quantum computers [1]. Decoherence-Free States (DFS) are considered as a possible solution to this problem. A set of trapped cold atoms placed in a DFS state will be immune against decoherence due to spontaneous emission. However, because of dipole-dipole interactions between atoms, induced dephasing effects are likely to destroy the coherence and drive the system out of its DFS [1, 2]. In this work, we study numerically the dynamics of a set of two-level atoms initially in a DFS with respect to dissipative processes by solving the master equation including both dissipative dynamics and dipole dipole interactions. We fo- cus our attention on the infuence of dipolar coupling on the radiated energy rate and coherence of the system as in [3]. In particular, by averaging over many realizations of close randomly distributed atomic positions, we show the formation of a superradiant-like pulse and we study its properties as a function of the dipolar coupling strength.
[1] D. A. Lidar & K. B. Whaley, Lectures Notes in Phys., Vol. 622, p83-120, Springer (2003).
[2] M. Gross & S. Haroche, Physics reports 93, 301-396 (1982).
[3] W. Feng, Y. Li & S-Y. Zhu, Phys. Rev. A 88, 033856 (2013).Symmetric N-qubit anticoherent states
http://hdl.handle.net/2268/169598
Title: Symmetric N-qubit anticoherent states
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<br/>Author, co-author: Baguette, Dorian; Bastin, Thierry; Martin, John
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<br/>Abstract: Entanglement is among the key features of quantum mechanics. In the last decade, a lot of efforts has been made to quantify the amount of entanglement of various multipartite states, either pure or mixed. In particular, the search for maximally entangled states (states maximizing certain measures of entanglement) has focused a great deal of attention, see e.g. Refs. [1–4].
In this work, we present a comprehensive study of maximally entangled symmetric N-qubit states with respect to the definition of Gisin [1]. According to this definition, a state is maximally entangled if all its one-qubit reduced density matrices are maximally mixed. These states maximize various entanglement measures, such as von Neumann and Meyer-Wallach entropies [5]. They are unique up to local unitaries within the class of states interconvertible under stochastic local operations and classical communication (SLOCC) [3]. Besides, they are conjectured to be maximally entangled with respect to the Negative Partial Transpose measure of entanglement [6]. As appreciated by B. Kraus, they play an important role in the determination of the local unitary equivalence of multiqubit states [7]. Moreover, they are maximally fragile (in the sense that they are the states which are the most sensitive to noise) and therefore have been proposed as ideal candidates for ultrasensitive sensors [1]. We provide general conditions for a symmetric state with an arbitrary number of qubits to be maximally entangled and identify families of SLOCC classes which do not contain any such states. We also compute various measure of entanglement associated with those states in order to characterize them further and find all maximally entangled states up to 4 qubits. We finally prove that maximally entangled states coincide with anticoherent states of order 1. According to the definition of Ref. [8], a symmetric state of N qubits is anticoherent to order t iff 〈(S·n)k〉 is independent of n for k = 1, . . . , t where n is a tridimensional unit vector and S is the collective spin operator associated to the N-qubit system.
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[7] B. Kraus, Phys. Rev. Lett. 104, 020504 (2010). [8] J. Zimba, EJTP 3, 10 (2006).Electrical characterization of pGeSn/nGe diodes
http://hdl.handle.net/2268/169299
Title: Electrical characterization of pGeSn/nGe diodes
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<br/>Author, co-author: Baert, Bruno; Gupta, Somya; Gencarelli, Federica; Loo, Roger; Simoen, Eddy; Nguyen, Ngoc Duy
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<br/>Abstract: I-V characteristics of pGeSn/nGe diodes have been measured and show very good properties.
Simulations of the same structure are able to reproduce most of the observed behavior and point to the predominating influence of parameters such as the band gap energy of the GeSn layer. C-V characteristics showing little frequency dependence have also been measured, and their analysis for the determination of the carrier concentration is confirmed by simulations. More investigations, including the effect of temperature and other defects at the interface or in the bulk of either layers are still required in order to explain some of the observed behaviors, notably the reverse saturation current.Mesoscale structures from magnetocapillary self-assembly
http://hdl.handle.net/2268/169286
Title: Mesoscale structures from magnetocapillary self-assembly
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<br/>Author, co-author: Vandewalle, Nicolas; Obara, Noriko; Lumay, Geoffroy
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<br/>Abstract: When identical soft ferromagnetic particles are suspended at some water-air interface, capillary
attraction is balanced by magnetic repulsion induced by a vertical magnetic field. By adjusting the magnetic field strength, the equilibrium interdistance between particles can be tuned. The aim of this paper is to study the ordering of particles for large assemblies. We have found an upper size limit above which the assembly collapses due to capillary effects. Before reaching this critical number of particles, defects are always present and limit the perfect ordering expected for that system. This is due to the curvature of the interface induced by the weight of the self-assembly.