Groups | Seminars || Courses | Outreach

Seminars

Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.

Spring/Summer 2016

February 1, 2016 Prof. Carlos Trallero Kansas State University Strong Field Physics: From isolated atoms to solids (Host: Tom Weinacht)

From isolated atoms to periodic solids, strong field physics with ultrashort pulsed fields has many common points. In addition to structure, the fast time scales used for the electric field allow to unravel the dynamics of the atoms and in some cases, the electrons. In this talk I will cover some of our results that make use of the commonality in the underlying science as well as discussing our recent optics developments that enable such science.

February 15, 2016 Prof. Phil Bucksbaum Stanford University Strong-field photoionization: What we can learn from all those electrons that DON'T end up making high harmonics. (Host: Tom Weinacht)

High harmonic generation is probably the most exciting new tool to come out of the study of strong laser-atom interactions, but only about one ionized electron in a thousand contributes to the high harmonic field. What about the rest? We've been studying them, and we find that they reveal much about the structure and attosecond dynamics of strongly driven atoms and molecules.

February 22, 2016 Dr. Sandra Eibenberger Harvard University Matter-wave interference and quantum-assisted metrology of large molecules (Host: Hal Metcalf)

In this presentation I will give an overview of my research on quantum interference experiments with complex organic molecules performed at the University of Vienna. The superposition principle is one of the pillars of quantum mechanics. Conceptually, for an isolated quantum particle, there should be no upper bound on mass or complexity for matter-wave interference. So what leads to the absence of quantum superposition in our macroscopic world? We perform near-field matter-wave interference experiments with molecules of increasing mass. I will present our results from quantum interference experiments with the most massive molecules to date – consisting oof more than 800 atoms and a mass of more than 10 000 amu [1]. Furthermore I will discuss quantum-assisted metrology in molecular matter-wave interferometry. The phase and amplitude of the interference patterns are highly sensitive to external perturbations. This can be utilized to investigate internal molecular properties that couple to the external perturbations. We investigate the role of electric moments in molecule interferometry by applying a well-controlled electric deflection field inside the interferometer [2]. This allows for measurements of static polarizabilities as well as for investigations of the effect of permanent electric dipole moments on the coherence of the matter waves [3]. Recently, we implemented a new method to measure optical absorption cross sections via molecule interferometry [4]. In this scheme, the recoil of single photons by the delocalized molecules inside the interferometer leads to measurable dephasing of the interference pattern. This allows to determine absolute optical absorption cross sections without the need of the vapor pressure of the molecules. These schemes are widely applicable to a large number of (bio)molecules in the future. 1] S. Eibenberger, S. Gerlich, M. Arndt, M. Mayor, J. Tüxen. Phys. Chem. Chem. Phys. 15, 14696(2013) [2] M. Berninger, A. Stefanov, S. Deachapunya, and M. Arndt. Phys. Rev. A. 76, 013607 (2007) [3] S. Eibenberger, S. Gerlich, M. Arndt, J. Tüxen, M. Mayor. New J. Phys. 13, 043033 (2011) [4] S. Eibenberger, X. Cheng, J.P. Cotter, M. Arndt. Phys. Rev. Lett. 112, 250402 (2014)

February 29, 2016 Patrick Walsh Purdue University Single-conformation IR and UV spectroscopy as a tool for understanding hydrogen bonding networks (Host: Tom Allison)

Single-conformation spectroscopy in the IR and UV is an important tool for physical chemists investigating a wide variety of problems. Topics of interest include combustion science, atmospheric chemistry, peptide folding, and solvation effects. In this talk I will focus on the insights gained into the hydrogen bonding networks present in two complementary circumstances. The first involves the network of water molecules in stepwise solvation of a typical flexible bichromophore (DPOE), and the second focuses on the amide-amide H-bonds influencing the inherent conformational preferences of small peptides containing the amino acid glutamine. In the case of 1,2-diphenoxyethane (DPOE) results from ground and electronic excited state conformation-specific infrared spectroscopy will be used to show the influences of stepwise solvation on the ground state structure and the excited state behavior of the solute molecule. In this instance, the water molecule can act as a reporter, revealing the localized nature of the excitations. In the second portion of this presentation I will talk about the inherent conformational preferences of several glutamine-containing molecules and the competition between sidechain-to-backbone and backbone-to-backbone hydrogen bonds. Glutamine plays an important role in key regions of proteins associated with neurodegenerative diseases; insight into the local conformations of glutamine should provide new and detailed information which can validate and improve computational methods used to model the pathogenic species structure.

March 28, 2016 Prof. Philip Johnson Stony Brook University Molecular Excitation Dynamics at Different Time Scales (Host: Tom Weinacht)

There has recently been an increase in interest in the details of the excitation dynamics of larger molecules because of its influence on the efficiency of organic LEDs and photocells.Many studies have focused on isolated molecules so as to better define the distinction between molecular and solid state properties. For some molecules, experiments done with light sources with time scales ranging from CW to femtoseconds have produced conflicting results.  For a series of aromatic molecules ranging from ethynylbenzene to anthracene, our nanosecond experiments have produced the interesting result of seeing triplet states that last for more than milliseconds, but are all created during the laser pulse. A kinetic model that includes multiphoton processes can be made to fit the experimental observations and to agree with the CW conclusion that there is negligible spin orbit coupling in these molecules.  Reports of ultrafast intersystem crossing in benzene at the one photon level, derived from models without multiphoton effects, continue to be at odds with what is seen at longer time scales.

April 25, 2016 Dr. Kristi Beck MIT Changing phase with just one photon (Host: Eden Figueroa)

Deterministic optical quantum logic requires a nonlinear quantum process to change the phase of a quantum optical state by pi through interactions with only one photon. In this talk, I will describe our method for interfacing two optical states using an atomic quantum memory inside of a high finesse optical resonator. Stored light in the memory interacts with light in the cavity. We measure a conditional phase shift of pi/6 and up to pi/3 by postselecting on photons that remain in the system longer than average. We also show that this interaction entangles the light that exits the system [1]. I further show that this entanglement can be used to manipulate the phase of the stored light or to detect stored light without entirely destroying it [2]. [1] KMB, M Hosseini, Y Duan, V Vuletic. arxiv:1512.02166 [2] M Hosseini, KMB, Y Duan, W Chen, V Vuletic. PRL 116, 033602 (2016)

May 2, 2016 Prof. Mikael Rechtsman Pennsylvania State University Aspects of photonic topological insulators (Host: Hal Metcalf)

I will present the observation of the topological protection of light - specifically, a photonic Floquet topological insulator. Topological insulators (TIs) are solid-state materials that are insulators in the bulk, but conduct electricity along their surfaces - and are intrinsically robust to disorder. In particular, when a surface electron in a TI encounters a defect, it simply goes around it without scattering, always exhibiting a quite strikingly – perfect transmission. The structure is an arrray of  coupled helical waveguides (the helicity generates a fictitious circularly-polarized electric field that leads to the TI behavior), and light propagating through it is "topologically protected" from scattering. Topological protection therefore has the potential to endow photonic devices with quantum Hall-like robustness. I will also discuss exotic topological systems where optics provides the ideal platform for realization, including quasicrystals and non-Hermitian systems

May 9, 2016 Prof. Manas Kulkarni City University of New York - CityTech Hydrodynamics of local excitations after an interaction quench in 1D cold atomic gases (Host: Dominik Schneble)

We discuss [1,2] the hydrodynamic approach to the study of the time evolution - induced by a quench - of local excitations in one dimension. We focus on interaction quenches: the considered protocol consists in creating a stable localized excitation propagating through the system, and then operating a sudden change of the interaction between the particles. To highlight the effect of the quench, we take the initial excitation to be a soliton. The quench splits the excitation into two packets moving in opposite directions, whose characteristics can be expressed in a universal way. Our treatment allows to describe the internal dynamics of these two packets in terms of the different velocities of their components. We confirm our analytical predictions through numerical simulations performed with the Gross-Pitaevskii equation and with the Calogero model (as an example of long range interactions and solvable with a parabolic confinement). Through the Calogero model we also discuss the effect of an external trapping on the protocol. The hydrodynamic approach shows that there is a difference between the bulk velocities of the propagating packets and the velocities of their peaks: it is possible to discriminate the two quantities, as we show through the comparison between numerical simulations and analytical estimates. In the realizations of the discussed quench protocol in a cold atom experiment, these different velocities are accessible through different measurement procedures. [1] F. Franchini, M. Kulkarni, A. Trombettoni, arXiv:1603.03051 [2] F. Franchini, A. Gromov, M. Kulkarni, A. Trombettoni, J. Phys. A: Math. Theor. 48 (2015) 28FT01

May 19, 2016 (Thurs) 4pm Prof. Hewa Abdullah Berkoti Salahaddin University, Iraq-Kurdistan Physics in Iraq & KRG and Higher Education at Salahaddin University (Host: Tom Bergeman)

1-    History of education in Iraq 2-    The Golden Years 3-    The Decline Years 4-    The Crisis Years 5-    UNESCO Office For Iraq; Higher Education in Iraq 6-    Physics in Iraq; Baghdad University College of Science 7-    Physics at the University of Mosul 8-    Physics at Salahaddin University 9-    Salahaddin University-Erbil

May 20, 2016 (Fri) 3pm Prof. Hewa Abdullah Berkoti Salahaddin University, Iraq-Kurdistan Contrastive study of potential energy functions of some diatomic molecules (Host: Tom Bergeman)

It was proposed that the iron hydride, FeH would be formed only on grains at the clouds, through the reaction of the adsorbed H atoms or H2 molecules with the adsorbed Fe atoms on the grains. The importance of FeH in Astrophysics presents an additional motivation to study its energetic, spectroscopic constants and Potential Energy Curves. The structural optimization for ground state of FeH was calculated by different theoretical methods, namely, Hartree-Fock (HF), the density functional theory (DFT), B3LYP, MP2 method and QCISD(T) methods and compared with available data from the literature. The single ionized form, cation and anion, were also calculated at the same level of calculations. Charges, dipole moment, geometrical parameters, molecular orbital energies and spectroscopic parameters were calculated and reported. Besides, the molecular ionization potential, electron affinity and dissociation energy were investigated.

May 23, 2016 (Mon) 12 noon, SCGP Room 102 Prof. Gerhard Rempe, Max Planck Institute for Quantum Optics, Germany Cavity Quantum Electrodynamics: A toolbox for quantum networking (Host: Eden Figueroa)

Optical cavities provide unparalleled capabilities in controlling the interaction between light and matter, and with this open up novel avenues for genuine quantum-mechanical applications like long-distance quantum networking and scalable quantum computation. With this backdrop the talk will highlight state of-the-art achievements including the nondestructive detection of an optical photon, the heralded interconversion of flying and stationary qubits, and the realization of long-standing dreams like quantum gates between individual qubits of both light and matter. The talk will also address counter-intuitive effects which occur when two emitters are coupled to one cavity.

May 30, 2016 Dr. Vladimir A. Yurovsky Tev Aviv University, Israel Consequences of non-trivial permutation symmetry in spinor quantum gases (Host: Tom Bergeman)

The first applications of the group-theoretical methods in quantum mechanics in works by Wigner, Heitler, and Dirac in 1926-1929 were devoted to the permutation symmetry. A general interest to this topic was lost after the discovery of the Pauli exclusion principle, which allows only permutation-symmetric or antisymmetric wavefunctions for bosons or fermions, respectively, and forbids non-Abelian irreducible representations of the symmetric group, where a wavefunction is transformed into a linear combination of several wavefunctions in the representation. Such representations can appear in physical systems with spinor and spatial degrees of freedom. In the talk I would like to present some consequences of the non-trivial permutation symmetry. They are the selection rules [1] for high-spin particles, the  suppression of the decay of states with well-defined spins in Bose gases [2], and modification of thermodynamic properties of Fermi gases in such states. The permutation symmetry leads to substantial change in the gas pressure and in the sound velocity. It also leads to second-order phase transitions that do not have analogs in gases with undefined total spin. These phase transitions are manifested as discontinuities in the specific heat and adiabatic compressibility. 1. V.A. Yurovsky, PRL 113, 200406 (2014). 2. V.A. Yurovsky, PRA 93, 023613 (2016).

June 3, 2016 (Fri) 1pm Dr. Elena Pavlenko University of Potsdam, Germany Hybrid nanolayer architectures for ultrafast acousto-plasmonics in soft matter (Host: Tom Allison)

Due to the exceptional sensitivity of gold nanorods (GNRs), they are widely used for various applications: ranging from treatment and imaging in biology to sensors in chemistry and physics. Most of these applications require the particles to be covered in a shell to tune their properties, prevent them from clustering or for a specific functionalization. Even though GNRs have been extensively used as sensing tool for decades, the structure and behavior of the GNRs/shell, shell/surrounding medium interfaces is not yet understood. It is important to understand these interfaces in order to improve the existing usage of GNRs and develop new applications. -- In this talk I will present a method which can provide information about the surrounding medium of GNRs incorporated into polyelectrolyte multilayers. Based on the layer-by-layer deposition of polyelectrolytes, we designed hybrid nanolayer-composites for integrated optoacoustic experiments. The femtosecond-laser-excitation of an Azobenzene-functionalized film launches GHz strain waves into a transparent polymer layer. The longitudinal plasmon resonance of GNRs' deposited on the surface is modified by the reversible viscoelastic response of the adjacent polymer and this yields information on their interface.

June 23, 2016 (Thurs) 4 pm Prof. Tilman Pfau University of Stuttgart, Germany 10 Years of Dipolar Gases: From Chromium to the Lanthanides (Host: Dominik Schneble)

D ipolar interactions in gases are fundamentally different from the usual van der Waals forces. Besides the anisotropy the dipolar interaction is nonlocal and as such allows for self organized structure formation. Ten years ago the first dipolar effects in a quantum gas were observed in an ultracold Chromium gas. By the use of a Feshbach resonance a purely dipolar quantum gas was observed three years after [1]. By now dipolar interaction effects have been observed in lattices and also for polar molecules. Recently it became possible to study degenerate gases of lanthanide atoms among which one finds the most magnetic atoms. The recent observation of their collisional properties includes the emergence of quantum chaos and very broad resonances [2,3]. Similar to the Rosensweig instability in classical magnetic ferrofluids self organized structure formation was expected. In our experiments with quantum gases of Dysprosium atoms we could recently observe the formation of a droplet crystal [4]. In contrast to theoretical mean field based predictions the superfluid droplets did not collapse. We find that this unexpected stability is due to beyond meanfield quantum corrections of the Lee-Huang-Yang type [5,6]. [1] T. Lahaye, C. Menotti, L. Santos, M. Lewenstein, and T. Pfau, "The physics of dipolar bosonic quantum gases", Rep. Prog. Phys. 72, 126401 (2009) [2] T. Maier, I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Pfau, K. Jachymski, P. S. Julienne, "Broad Feshbach resonances in collisions of ultracold Dysprosium atoms", Phys. Rev. A 92, 060702(R) (2015) [3] T. Maier, H. Kadau, M. Schmitt, M. Wenzel, I. Ferrier-Barbut, T. Pfau, A. Frisch, S. Baier, K. Aikawa, L. Chomaz, M. J. Mark, F. Ferlaino, C. Makrides, E. Tiesinga, A. Petrov, S. Kotochigova, "Emergence of chaotic scattering in ultracold Er and Dy", , Phys. Rev. X 5, 041029 (2015) [4] H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, T. Pfau "Observing the Rosensweig instability of a quantum ferrofluid", Nature 530, 194 (2016) [5] T. D. Lee, K. Huang, and C. N. Yang, " Eigenvalues and Eigenfunctions of a Bose System of Hard Spheres and Its Low-Temperature Properties", Phys. Rev. 106, 1135 (1957) [6] I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, T. Pfau, "Observation of quantum droplets in a strongly dipolar Bose gas", Phys. Rev. Lett. 116, 215301 (2016)

August 9, 2016 (Tues) 4 pm Prof. Dajun Wang The Chinese University of Hong Kong, Hong Kong, China An ultracold gas of ground-state dipolar 23Na87Rb molecules (Host: Tom Bergeman)

In this talk, I will report our recent work on the production of an ultracold sample of absolute ground-state 23Na87Rb molecules with large induced electric dipole moments. Starting from weakly-bound Feshbach molecules formed via magneto-association, the lowest rovibrational and hyperfine state is populated following a high efficiency and high resolution two-photon Raman process. The high purity absolute ground-state sample has up to 8000 molecules and number densities of more than 10^11 cm-3. With an external electric field, we have induced an effective dipole moment over 1 Debye, making strong and long-range dipolar interactions realistic. Bi-molecular exchange reaction between ground-state 23Na87Rb molecules is endothermic, but we still observed a rather fast population decay in the lifetime measurement. If time allows, I will also discuss our new molecular collision experiments aiming at understanding the loss mechanism for chemically stable ultracold dipolar molecules.

2016