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.

Fall 2013

September 3, 2013 at 11:00am Prof. Michele Modugno, University of the Basque Country, Bilbao (Spain) Tight binding models for ultracold atoms in optical lattices (Host: Dominik Schneble)

I will discuss how to construct tight-binding models for ultracold atoms in optical lattices, by means of the maximally localized Wannier functions for composite bands. Specific examples will be given for the case graphene-like potentials with two degenerate minima per unit cell, where a tight-binding model with up to third-nearest neighbors is capable to reproduce the structure of the Dirac points in a range of typical experimental parameters (see the recent experiment by Tarruell et al., Nature 483, 302 (2012)). I will also briefly review other recent theoretical results, including anomalous Bloch oscillations, shortcuts to adiabaticity, and quantum backflow.

September 17, 2013 (P&A COLLOQIUM) Prof. Brian DeMarco University of Illinois at Urbana Champaign Ultracold Disordered Quantum Gases (Host: Dominik Schneble)

Disorder is the rule, rather than the exception, in nature. Despite this, we understand little about how disorder affects interacting quantum matter. I will give an overview of our experiments using ultracold atom gases to probe paradigms of interacting disordered quantum particles. We introduce disorder to naturally clean atomic gases cooled to billionths of a degree above absolute zero using focused optical speckle. I will explain how we observe Anderson localization-a spectacular phenomenon in which interference prevents waves from propagating in a disordered medium-of quantum matter in three dimensions. I will also show how we combine speckle with an optical crystal to emulate a completely tunable and precisely characterized disordered quantum solid. In these optical lattice experiments, we realize disordered Hubbard models that we use to answer critical questions regarding how disorder impacts the properties of electronic solids, such as superconductors and metals.

September 20, 2013 at 1:00pm Dr. Stephen Hogan, University College London (UK) Guiding, decelerating and trapping cold Rydberg atoms (Host: Hal Metcalf)

The development of methods to manipulate the translational motion of atoms and molecules in Rydberg states using inhomogeneous electric fields [1,2], has led to the realisation of Rydberg atom and molecule optics elements including mirrors [3], lenses [4] and traps [5-6]. These devices have applications in (i) the development of hybrid approaches to quantum information processing involving Rydberg atoms and microwave circuits, (ii) the preparation of gas-phase molecular samples at temperatures below 1 K, for studies of slow decay processes and low-energy scattering, and (iii) the confinement and manipulation of anti-hydrogen atoms. In this talk I will describe experiments with hydrogen Rydberg atoms in three-dimensional electrostatic traps, with an emphasis on the role of radiative processes in the decay of the trapped samples, and recently developed surface-based guides, decelerators and traps for atoms and molecules in Rydberg states. [1] W. H. Wing, Phys. Rev. Lett., 45, 631 (1980) [2] T. Breeden and H. Metcalf, Phys. Rev. Lett., 47, 1726 (1981) [3] E. Vliegen and F. Merkt, Phys. Rev. Lett., 97, 033002 (2006) [4] E. Vliegen, P. Limacher and F. Merkt, Eur. Phys. J. D, 40, 73 (2006) [5] S. D. Hogan and F. Merkt, Phys. Rev. Lett., 100, 043001 (2008) [6] S. D. Hogan, P. Allmendinger, H. Sassmannshausen, H. Schmutz and F. Merkt, Phys. Rev. Lett., 108, 063008 (2012)

October 14, 2013 Dr. Michael Spanner, NRC, Ottawa Toward ab-initio simulations of strong-field ionization of molecules (Host: Tom Weinacht)

A growing trend in today's ultrafast laser community is strong-field attosecond science.  A core process in attosecond physics is ultrafast strong-field ionization.  In this process, a strong laser field ionizes an atom or molecule during a single half-cycle of the driving laser field.  Sub-cycle ionization leads to a number of interesting phenomema including high-harmonic generation and attosecond pulse generation.  In this talk, I will outline some recent attempts at modelling sub-cycle strong-field ionization from molecules from an ab-initio-type electronic structure perspective.

October 21, 2013 Chris Corder,  Brian Arnold, and Hal Metcalf, SBU Laser Cooling of Helium Metastable Atom Beams

This is the first of an experiment to have some of our seminar days devoted to research within our five groups.  This talk will be given by Chris Corder, Brian Arnold, and Hal Metcalf together.  It will begin with a brief discussion of the role of energy, momentum, and entropy in laser cooling.  The underlying background will address the question of whether laser cooling is possible without spontaneous emission.  Chris will then describe how the bichromatic optical force can test experimentally the topic of laser cooling without spontaneous emission.  He will describe the bichromatic dressed atom picture, his apparatus, the details of avoiding spontaneous emission, and present his results. Brian Arnold has done Monte Carlo simulations of the experiment, and he will describe how the program works and its results, and together Chris and Brian will compare the data and the simulation results

November 4, 2013 Dr. Valentin Murg, Universität Wien (Austria) Adiabatic Preparation of a Heisenberg Antiferromagnet Using an Optical Superlattice (Host: Dominik Schneble/Vladimir Korepin)

We analyze the possibility to prepare a Heisenberg antiferromagnet with cold fermions in optical lattices, starting from a band insulator and adiabatically changing the lattice potential. The numerical simulation of the dynamics in 1D allows us to identify the conditions for success, and to study the influence that the presence of holes in the initial state may have on the protocol. We also extend our results to two-dimensional systems.

November 11, 2013 Vincent Tagliamonti, University of Connecticut, Storrs Strong Field Ionization of a Diatomic Molecule using 1w2w Ultrafast Laser Pulses (Host: Tom Weinacht)

I will discuss two experiments examining the effects of strong field ionization in diatomic iodine in the presence of a two-color (1w2w) femtosecond laser pulse.  The spatial asymmetry of the 1w2w pulse breaks the spatial symmetry of ionization allowing for control over directions of ion yields while providing insight into the physics of ionization. In particular, this work studies excited states of the doubly ionized molecule which are produced via two processes, described as asymmetric production and depletion of a charge asymmetric dissociation channel. In the production experiment a pump-probe technique is used to excite I2 to the B state of the neutral which is subsequently ionized by a two-color (800- and 400-nm) probe pulse. By varying the relative phase of the two colors we are able to probe the asymmetric dissociation of (I2)2+ → I2+ + I and we observe spatial asymmetries in the ion yield of this (2,0) channel. Because the durations (35 fs) of the pump and probe pulses are much shorter than the vibrational period of the B state (700 fs) we can fully resolve the dynamics as a function of internuclear separation R.  The depletion experiment uses a pump pulse at 800 nm to create a wave packet in the(2,0). As the molecule dissociates, a two-color probe pulse is used to study the dynamics as a function of R.  We find a critical region of RÂin which there is spatially asymmetric enhanced ionization of the (2,0) channel to a counterintuitive (1,2) channel. In this region the neutral iodine atom is ionized such that one electron is released to the continuum and another is transferred to the 2+ ion. The production experiment results in a description of ionization into coherent mixed states of the dication while the depletion experiment reveals prominent multielectron dynamics near R critical.  The first experimental evidence for enhanced ionization in 1994 by Corkum, et al, and the applicability of one and two electron ionization dynamics will be discussed through simple models and quantum mechanical simulations.

November 18, 2013 Dr. Arthur Mills, University of British Columbia XUV Frequency Combs for Photoemission Spectroscopy of Condensed Matter Systems (Host: Tom Allision )

XUV frequency combs generated via high harmonic generation in femtosecond enhancement cavities (fsEC) are coherent, table-top sources of XUV and VUV capable of operating at very high repetition rates (>10 MHz) and high flux (>10^12 photons/s). Given this level of performance these fsEC sources are beginning to see use in more experiments as their characteristics are better understood, optimized and controlled. In this talk I will discuss our progress toward application of fsEC sources (in the 6-25 eV photon energy range) to angle-resolved photoemission spectroscopy (ARPES) of condensed matter systems, including equilibrium studies and time-resolved pump-probe measurements.

November 25, 2013 Dr. Doug Broege, Stanford University Impulsive alignment in dense molecular ensembles: high temperatures and new directions (Host: Tom Weinacht )

An aligned molecular ensemble is useful in many experiments geared toward structure determination ranging from spectroscopy to x-ray scattering.  One technique, known as impulsive, or field-free alignment, is the result of a strong torque applied over a short period of time.  The wavepacket created by this torque exhibits field free alignment along the axis of polarization immediately following the impulse, and at revivals.  We describe measurements of these wavepackets carried out at temperatures over 400 degrees K in molecular iodine, and the effects that centrifugal distortion and vibrational excitation have on its revivals.  We will also discuss a technique developed to align molecular ensembles along the direction of laser propagation without the need for a crossed-beam geometry.

December 9, 2013 Dr. Sid Cahn, Yale University The Search for Nuclear Anapole Moments in Diatomic Molecules (Host: Hal Metalf)

Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from exchange of the Z^0 boson (parameterized by the electroweak coupling constants C2{P,N}) between electrons and the nucleus, and from the interaction of electrons with the nuclear anapole moment, a parity-odd magnetic moment. The latter scales with the nucleon number A of the nucleus as A^(3/2), while the Z^0 coupling is independent of A; the former will be the dominant source of NSD-PNC in nuclei with A = 20. NSD-PNC effects can be dramatically amplified in diatomic molecules by bringing two levels of opposite parity close to degeneracy in a strong magnetic field. This opens the prospect for measurements across a broad range of nuclei. As a precursor to the measurement of the nuclear anapole moment of 137Ba, we have experimentally observed and characterized opposite-parity level crossings in 138BaF. These are found to be in excellent agreement with parameter-free predictions and indicate that the sensitivity necessary for NSD-PNC measurements should be within reach.

Wed, December 11, 2013, 2:30pm Dr. Andrew Grier, Laboratoire Kastler-Brossel, ENS, Paris Atoms at Resonance: Scattering and losses of a Bose gas at unitarity (Host: Dominik Schneble)

Tunability of the two-body scattering properties in ultracold atomic gases has proven to be a powerful tool in recent years, providing the first direct experimental evidence of long-predicted Efimov states and allowing for quantum simulation of unreachable or computationally intractable systems.  In this talk, we will review recent experimental and theoretical results centered around ultracold atomic Bose gases taken close to a scattering resonance where the two-body scattering cross-section diverges.  We will focus on measurements of the decay of a non-degenerate gas both at and in the vicinity of the scattering resonance due to three-body recombination processes.  We will present a theoretical framework for understanding the rate of these events based on universal Efimovian physics, and use this theory to explore how one might stabilize a unitary Bose gas.

last updated 11/13/2013