Fecha  Evento 

15/12/2017  15/12/2017  Geometry invariant phenomena in near zero index media Abstract: Continuous media and metamaterials with a nearzero refractive index (NZI media) provide alternative pathways for the control and manipulation of lightmatter interactions. The exotic behavior of NZI media is rooted in the fact that the wavelength gets effectively stretched as the refractive index vanishes. This allows for pathological solutions to the wave equation, including spatially static fields distributions which nevertheless dynamically oscillate in time. This paradoxical behavior gives access to a regime of qualitatively different wave dynamics, where the importance of the geometry is lessened, and certain observables are invariant with respect to geometrical deformations, even including changes in the topology of the system.
In this talk, I’ll review and discuss some of the geometryinvariant phenomena related to nearzeroindex media. Examples will include: (i) transmission (tunneling) of waves through deformed waveguides. (ii) Unconventional resonators supporting modes whose eigenfrequency is independent of the geometry of their external boundary. (iii) Violation of effective medium theory geometrical restrictions, enabling, for example, single unitcell metamaterials. (iv) Existence of bound states in open 3D compact resonators with arbitrarily shaped boundaries. Different technological applications and implementations of these concepts will be discussed.
Más información: http://www.ifimac.uam.es/category/seminars/

14/12/2017  14/12/2017  Polariton lattices a novel platform for analogue simulation
Abstract: A large variety of computationally intractable systems can be mapped into certain univer sal classical spin models such as an Ising, X Y or Heisenberg models that are characterised by given degrees of freedom, “spins”, their interactions, “couplings,” and their associated cost function, “Hamiltonian”. Various physical platforms have been proposed to simulate such models using superconducting qubits, optical lattices, coupled lasers etc. We introduce polariton lattices as a new platform for analogue simula tion; based on wellestablished semi conductor and optical control technolo gies polariton simulators allow for rapid scalability, ease of tunability and ef fortless readability. Polariton conden sates can be imprinted into any two dimensional lattices either by spatial modulation of the pumping laser or by lithographic techniques during the growth process, offering straightforward scalability. In the case of optically imprinted polariton lattices with freely propagating polariton condensates, we recently demonstrated that the phase configuration acquired in a polariton dyad or triad is chosen so as to max imise polariton occupancy [1], while by expanding to square, and rhombic lat tices as well as to arbitrary polariton graphs we simulated annealing of the X Y Hamiltonian through bosonic stim ulation [2]. The bottomup approach of bosonic stimulation is achieved here by gradually increasing the excitation density to con densation threshold. This is an advantage over classical or quantum annealing techniques, where the global ground state is reached through transitions over metastable excited states with an increase of the cost of the search with the size of the system. By controlling the separation distance, inplane wavevector, and spin of the injected condensates in polariton graphs, we acquire several degrees of freedom in the tunability of intersite interactions, whilst the continuous coupling of polaritons to free photons offers effortless readability of all the characteristics of the polariton condensates such as energy, momentum, spin, and most critically their phase. The above constitute a unique toolbox for realising intriguing discrete giant vortices, controllable next nearest neighbour interactions, dynamic phase transitions and simulating artificial solids. References:
[1] H. Ohadi, R.L. Gregory, T. Freegarde, Y.G. Rubo, A.V. Kavokin, N.G. Berloff, and P.G. Lagoudakis, Phys. Rev. X, 6, 031032 (2016) [2] Natalia G. Berloff, Matteo Silva, Kirill Kalinin, Alexis Askitopoulos, Julian D. T¨opfer, Pasquale Cilibrizzi, Wolfgang Langbein and Pavlos G. Lagoudakis, Nature Materials in print DOI: 10.1038/NMAT4971 (2017)
Más información: http://www.ifimac.uam.es/category/seminars/ 
12/12/2017  12/12/2017  Charge and energy noise in ac driven conductors
Abstract: The timedependent driving of nanoscale conductors allows for the controlled creation of singleelectron excitations. This effect has been demonstrated experimentally both by application of timedependent driving to gates coupled to confined systems, such as quantum dots [1], and by specifically shaped acdriving of twodimensional conductors [2,3]. However, the spectral properties of the injected signal are in general not known; moreover, the particle emission goes along with the excitation of electronhole pairs with some unknown energy distribution. These issues can be addressed by studying fluctuations in the detected currents: not only do such fluctuations provide more insight into how to increase the precision of the singleparticle emission, but also they allow for obtaining more information about the character of the emitted signal.
Here, I will present a theoretical study of charge and energy currents and their fluctuations in coherent conductors driven by different types of timeperiodic bias voltages, based on a scattering matrix approach [4,5]. Specifically, we investigate the role of electronlike and holelike excitations created by the driving in the charge current noise, where they only contribute separately. In contrast, additional features due to electronhole correlations appear in the energy noise. We then compare two different types of driving schemes [6], that is for a driven mesoscopic capacitor [1] as well as for a Lorentzianshaped bias voltage [3], which do not differ in the number of injected particles, but only in their energetic properties. Finally, I will discuss proposals for the detection of charge and energy noise, either through power fluctuations [4], or via frequencydependent temperature and electrochemicalpotential fluctuations in a probe reservoir [7]. References: [1] G. Fève, A. Mahé, J.M. Berroir, T. Kontos, B. Plaçais, D. C. Glattli, A. Cavanna, B. Etienne, Y. Jin: Science 316, 1169 (2007). [2] J. Gabelli and B. Reulet, Phys. Rev. B 87, 075403 (2013). [3] J. Dubois, T. Jullien, F. Portier, P. Roche, A. Cavanna, Y. Jin, W. Wegscheider, P. Roulleau, and D. C. Glattli, Nature 502, 659 (2013). [4] F. Battista, F. Haupt, and J. Splettstoesser, Phys. Rev. B 90, 085418 (2014) [5] F. Battista, F. Haupt, and J. Splettstoesser, J. Phys. Conf. Ser. 568, 052008 (2014) [6] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation [7] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation.
Más información: http://www.ifimac.uam.es/category/seminars/ 
01/12/2017  01/12/2017  Centrosomes and exosomes molecualr pacemakers of immune synapse

15/11/2017  15/11/2017  Pair correlation function of a 2D molecular gas directly visualized by scanning tunneling microscopy
Abstract: The state of matter in fluid phases, determined by the interactions between particles, can be characterized by a pair correlation function (PCF). At the nanoscale, the PCF has been so far obtained experimentally only by means of reciprocalspace techniques. We use scanning tunneling microscopy (STM) at room temperature in combination with latticegas kinetic Monte Carlo (KMC) simulations to study a twodimensional gas of highly mobile molecules of fluorinated copper phthalocyanine on a Si(111)/Tl(1×1) surface. A relatively slow mechanism of STM image acquisition results in timeaveraging of molecular occurrence under the STM tip. We prove by the KMC simulations that in the proximity of fixed molecules STM images represent the PCF. We demonstrate that STM is capable of visualizing directly the pair correlation function in real space.
Más información: http://www.ifimac.uam.es/category/seminars/

Fecha  Evento 

15/12/2017  15/12/2017  Geometry invariant phenomena in near zero index media Abstract: Continuous media and metamaterials with a nearzero refractive index (NZI media) provide alternative pathways for the control and manipulation of lightmatter interactions. The exotic behavior of NZI media is rooted in the fact that the wavelength gets effectively stretched as the refractive index vanishes. This allows for pathological solutions to the wave equation, including spatially static fields distributions which nevertheless dynamically oscillate in time. This paradoxical behavior gives access to a regime of qualitatively different wave dynamics, where the importance of the geometry is lessened, and certain observables are invariant with respect to geometrical deformations, even including changes in the topology of the system.
In this talk, I’ll review and discuss some of the geometryinvariant phenomena related to nearzeroindex media. Examples will include: (i) transmission (tunneling) of waves through deformed waveguides. (ii) Unconventional resonators supporting modes whose eigenfrequency is independent of the geometry of their external boundary. (iii) Violation of effective medium theory geometrical restrictions, enabling, for example, single unitcell metamaterials. (iv) Existence of bound states in open 3D compact resonators with arbitrarily shaped boundaries. Different technological applications and implementations of these concepts will be discussed.
Más información: http://www.ifimac.uam.es/category/seminars/

14/12/2017  14/12/2017  Polariton lattices a novel platform for analogue simulation
Abstract: A large variety of computationally intractable systems can be mapped into certain univer sal classical spin models such as an Ising, X Y or Heisenberg models that are characterised by given degrees of freedom, “spins”, their interactions, “couplings,” and their associated cost function, “Hamiltonian”. Various physical platforms have been proposed to simulate such models using superconducting qubits, optical lattices, coupled lasers etc. We introduce polariton lattices as a new platform for analogue simula tion; based on wellestablished semi conductor and optical control technolo gies polariton simulators allow for rapid scalability, ease of tunability and ef fortless readability. Polariton conden sates can be imprinted into any two dimensional lattices either by spatial modulation of the pumping laser or by lithographic techniques during the growth process, offering straightforward scalability. In the case of optically imprinted polariton lattices with freely propagating polariton condensates, we recently demonstrated that the phase configuration acquired in a polariton dyad or triad is chosen so as to max imise polariton occupancy [1], while by expanding to square, and rhombic lat tices as well as to arbitrary polariton graphs we simulated annealing of the X Y Hamiltonian through bosonic stim ulation [2]. The bottomup approach of bosonic stimulation is achieved here by gradually increasing the excitation density to con densation threshold. This is an advantage over classical or quantum annealing techniques, where the global ground state is reached through transitions over metastable excited states with an increase of the cost of the search with the size of the system. By controlling the separation distance, inplane wavevector, and spin of the injected condensates in polariton graphs, we acquire several degrees of freedom in the tunability of intersite interactions, whilst the continuous coupling of polaritons to free photons offers effortless readability of all the characteristics of the polariton condensates such as energy, momentum, spin, and most critically their phase. The above constitute a unique toolbox for realising intriguing discrete giant vortices, controllable next nearest neighbour interactions, dynamic phase transitions and simulating artificial solids. References:
[1] H. Ohadi, R.L. Gregory, T. Freegarde, Y.G. Rubo, A.V. Kavokin, N.G. Berloff, and P.G. Lagoudakis, Phys. Rev. X, 6, 031032 (2016) [2] Natalia G. Berloff, Matteo Silva, Kirill Kalinin, Alexis Askitopoulos, Julian D. T¨opfer, Pasquale Cilibrizzi, Wolfgang Langbein and Pavlos G. Lagoudakis, Nature Materials in print DOI: 10.1038/NMAT4971 (2017)
Más información: http://www.ifimac.uam.es/category/seminars/ 
12/12/2017  12/12/2017  Charge and energy noise in ac driven conductors
Abstract: The timedependent driving of nanoscale conductors allows for the controlled creation of singleelectron excitations. This effect has been demonstrated experimentally both by application of timedependent driving to gates coupled to confined systems, such as quantum dots [1], and by specifically shaped acdriving of twodimensional conductors [2,3]. However, the spectral properties of the injected signal are in general not known; moreover, the particle emission goes along with the excitation of electronhole pairs with some unknown energy distribution. These issues can be addressed by studying fluctuations in the detected currents: not only do such fluctuations provide more insight into how to increase the precision of the singleparticle emission, but also they allow for obtaining more information about the character of the emitted signal.
Here, I will present a theoretical study of charge and energy currents and their fluctuations in coherent conductors driven by different types of timeperiodic bias voltages, based on a scattering matrix approach [4,5]. Specifically, we investigate the role of electronlike and holelike excitations created by the driving in the charge current noise, where they only contribute separately. In contrast, additional features due to electronhole correlations appear in the energy noise. We then compare two different types of driving schemes [6], that is for a driven mesoscopic capacitor [1] as well as for a Lorentzianshaped bias voltage [3], which do not differ in the number of injected particles, but only in their energetic properties. Finally, I will discuss proposals for the detection of charge and energy noise, either through power fluctuations [4], or via frequencydependent temperature and electrochemicalpotential fluctuations in a probe reservoir [7]. References: [1] G. Fève, A. Mahé, J.M. Berroir, T. Kontos, B. Plaçais, D. C. Glattli, A. Cavanna, B. Etienne, Y. Jin: Science 316, 1169 (2007). [2] J. Gabelli and B. Reulet, Phys. Rev. B 87, 075403 (2013). [3] J. Dubois, T. Jullien, F. Portier, P. Roche, A. Cavanna, Y. Jin, W. Wegscheider, P. Roulleau, and D. C. Glattli, Nature 502, 659 (2013). [4] F. Battista, F. Haupt, and J. Splettstoesser, Phys. Rev. B 90, 085418 (2014) [5] F. Battista, F. Haupt, and J. Splettstoesser, J. Phys. Conf. Ser. 568, 052008 (2014) [6] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation [7] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation.
Más información: http://www.ifimac.uam.es/category/seminars/ 
01/12/2017  01/12/2017  Centrosomes and exosomes molecualr pacemakers of immune synapse

15/11/2017  15/11/2017  Pair correlation function of a 2D molecular gas directly visualized by scanning tunneling microscopy
Abstract: The state of matter in fluid phases, determined by the interactions between particles, can be characterized by a pair correlation function (PCF). At the nanoscale, the PCF has been so far obtained experimentally only by means of reciprocalspace techniques. We use scanning tunneling microscopy (STM) at room temperature in combination with latticegas kinetic Monte Carlo (KMC) simulations to study a twodimensional gas of highly mobile molecules of fluorinated copper phthalocyanine on a Si(111)/Tl(1×1) surface. A relatively slow mechanism of STM image acquisition results in timeaveraging of molecular occurrence under the STM tip. We prove by the KMC simulations that in the proximity of fixed molecules STM images represent the PCF. We demonstrate that STM is capable of visualizing directly the pair correlation function in real space.
Más información: http://www.ifimac.uam.es/category/seminars/
