Groups | Seminars || Courses | Outreach


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 2017

January 30, 2017

Andrew Koller
JILA/University of Colorado, Boulder

Collective spin dynamics in a weakly interacting Fermi gas

(Host: Hal Metcalf)

Magnetic correlations in materials are generated by a variety of complex mechanisms, including spin exchange and electronic motion, occurring both in combination and in competition. The interplay of spin and motional mechanisms is believed to be at the heart of rich phenomena including high temperature superconductivity. Ultracold atomic Fermi gases, with precisely controllable parameters, represent a versatile platform with which to investigate the interplay of spin and motion in out-of-equilibrium settings. In this talk we will discuss the spin dynamics of a weakly interacting two-component Fermi gas subjected to a magnetic field gradient. In contrast to prior investigations done in the unitary limit where the magnetization relaxes very quickly, in this regime large oscillations of the magnetization are driven by single particle dynamics, and spin and motional effects must be treated at the same level. We treat the problem using a spin model formalism in energy space which predicts a number of interesting effects such as the global spreading of spin correlations.

February 13, 2017

Prof. Nathan Gemelke
Pennsylvania State University

Analog Models of Gauge and Gauge-Gravity Dynamics in Cold-Atom Systems

(Host: Dominik Schneble)

The quantum mechanics of gauge fields in dynamical systems is often plaguedby subtleties related to quantization. For example, the existence of a mass for the gauge bosons at long length and time scales in quantum chromodynamics and electroweak physics is complicated by questions relating to confinement.  Similar questions arise in gauge-field formulations of quantum gravity, in which the dynamics of spacetime are treated as gauge excitations on a disordered network or graph. It is helpful in understanding these problems to develop laboratory methods to explore the dynamical evolution of systems with quantum degrees of freedom which may be described by gauge fields.  Cold atoms offer one such possibility, in which weakly dissipative couplings between atom and light can be described by dynamical gauge fields, and investigated over large dynamic ranges of length and time.I will describe one such system, which through combined effects of relativistic dynamics of slow light and disorder, leads to Higgs-like transitions and simple models for quantum gravity.

February 20, 2017

Prof. Jeffrey Moses
Cornell University

New optical sources for physics and spectroscopy based on an old trick of atomic physics

(Host: Tom Allison)

From strong-field optical physics to nonlinear phononics and femtosecond-resolved optical spectroscopy, developing fields of optical physics are making demands for coherent light sources of greater bandwidth, greater intensity, and in new ranges of the electromagnetic spectrum. Yet, lasers and nonlinear optical sources of coherent light have been limited by the same old problems of narrow gain bandwidth and a trade-off between bandwidth and gain. Here we show how an old trick of atomic physics, rapid adiabatic passage, can get around these old limitations. Here the Landau-Zener adiabatic transition is between photons, and the physical platform is nonlinear optical frequency conversion, with conversion dynamics in direct analogy and mathematically isomorphic to those of the linear Schrödinger equation for a coupled two-level system. We’ll review the physics of the process and our latest experimental results, which include the production of arbitrarily shapeable and intense mid-infrared light pulses covering more than an octave of optical bandwidth. We intend to use these pulses for a wide range of time-resolved spectroscopy and strong-field light-matter interaction experiments.


February 21, 2017 (4pm)
P&A colloquium

Prof. Jack Harris
Yale University

Topological physics with a pair of oscillators: beyond Berry's phase via exceptional points

(Host: Eden Figueroa/Dominik Schneble)

Topological phenomena appear in a number of physical systems, from exotic quantum states to carefully engineered waveguides. These phenomena offer new forms of control, and are also intriguing in their own right. I will describe a topological feature that is generically present in one of nature's simplest systems: a pair of coupled oscillators. I will describe experiments in which we demonstrate this feature and use it to achieve topological control over the vibrational modes of a mechanical oscillator. Although these effects are classical, our experiments are carried out using an optomechanical device that is also capable of detecting the membrane's quantum fluctuations. I will describe some prospects for studying the interplay of topological and quantum effects in such a systemba

February 27, 2017

Dr. Daniel Greif
Harvard University

Exploring Quantum Antiferromagnets with Single-Site Resolution

(Host: Dominik Schneble)

Strongly correlated electron systems such as high-temperature superconductors and pseudo-gap states are a cornerstone of modern condensed matter research. A complementary approach to studying solid-state systems is to build an experimentally tunable quantum system governed by the Hubbard model, which is thought to qualitatively describe these systems but is difficult to understand theoretically. Ultracold fermionic quantum gases in optical lattices provide a clean and tunable implementation of the Hubbard model. At the same time, optical microscopy in these systems gives access to single-site observables and correlation functions, and provides dynamic control of the potential landscape at the single-site level. So far, ultracold atom experiments have not been able to reach the low-temperature regime of the Hubbard model, which becomes particularly interesting when doped. Here we report on the observation of antiferromagnetic long-range order in a repulsively interacting Fermi gas of Li-6 atoms on a 2D square lattice containing about 80 sites. The ordered state is directly detected from a peak in the spin structure factor and a diverging correlation length of the spin correlation function. When doping away from half-filling into a numerically intractable regime, we find that long-range order extends to doping concentrations of about 15%. Our results open the path for a controlled study of the low-temperature phase diagram of the Hubbard model.

March 6, 2017

Prof. Irina Novikova
College of William & Mary

Spatial Mode Structure of Atom-Generated Squeezed Vacuum

(Host: Eden Figueroa)

We study the spatial mode structure in the squeezed vacuum produced via polarization self-rotation interaction of an ensemble of Rb atoms and a strong linearly polarized laser field. In particular, we show that to accurately predict the measured quadrature noise of the output squeezed vacuum field, the analysis must include several higher-order spatial modes. The quantum fluctuations for each such mode may be independently modified by the interaction with atoms, thus affecting the overall detected quadrature noise and potentially limiting the available amount of squeezing. We also investigate the role of the optical depth of the atomic medium.

 March 7, 2017 (4pm)
P&A Colloquium

Prof. Irina Novikova
College of William & Mary

Cool Quantum Optics with Hot Atoms

(Host: Eden Figueroa)

Efficient and reliable quantum communication will require the control of the quantum state of both photons and atoms. In this talk I will discuss a possible realization of strong coupling between quantum optical field and collective spin excitation in atomic vapor via  electromagnetically induced transparency, as well as possible applications of the effect for precision metrology, quantum memory and generation of non-classical light.

April 10, 2017

Prof.  Navid Vafaei-Najafabadi
Stony Brook University

Laser Acceleration of Electrons in a Laser Wakefield Accelerator

(Host: Tom Weinacht)

A plasma wave driven by a high intensity laser can accelerate electrons at a rate that is a thousand times higher than that of a conventional accelerator. This laser wakefield accelerator (LWFA) technology has the potential for revolutionizing the particle acceleration field by creating table-top electron accelerators as well as particle colliders that are orders of magnitude shorter than the currently operating machines. Additionally, because of the linear focusing force in the plasma wave, the electrons undergo transverse oscillations, which creates x-ray photons with energies of tens of MeV. In the ideal regime of the laser wakefield accelerator, the laser pulse occupies less than half of the plasma wave, and therefore will not overlap with the accelerating electrons, which reside in the back half of this wave. In this talk, I will explore how the acceleration mechanism is modified if the laser field overlaps these electrons. In particular, I will show that in the presence of the ion column, the transverse field of the laser can couple to the longitudinal momentum of electrons in a process that is similar to inverse free electron laser (IFEL). Through this process, called direct laser acceleration (DLA), the transverse laser field can provide a significant boost to the energy of the accelerating electrons. The significant role that DLA can play in increasing the energy of the electrons in an LWFA was recently demonstrated experimentally and confirmed through 3D simulations. I will discuss these results as well as the implications of DLA for increasing the yield and energy of the x-ray radiation that may be obtained from a table top machine based on an LWFA.

April 24, 2017

Prof. Bryce Gadway
University of Illinois, Urbana-Champaign

Engineering topological quantum fluids with flying matter waves

(Host: Dominik Schneble)

Since their realization over two decades ago, quantum gases of dilute atomic vapors have provided a unique playground for the exploration of many-body quantum physics. In particular, precisely controlled systems of ultracold atoms in optical lattices naturally mimic the behavior of electrons in crystal lattices, and have been used for the quantum simulation of complex electronic matter. To expand the types of systems that can be quantum simulated, and to enable the exploration of entirely new forms of matter, many groups are working to expand the quantum simulation toolbox through the engineering of novel lattice structures, designer artificial gauge fields, and novel interactions. In this talk, I will discuss a new approach developed in our group for the realization of effective gauge fields and nontrivial topological order in neutral atomic gases. Our technique is based on a mapping between atomic momentum states and sites of a synthetic lattice. Compared to real-space lattices, the high degree of control over individual laser-driven transitions between momentum states permits an essentially universal engineering of designer tight-binding lattices. I’ll discuss some recent studies of topological and disordered lattices, the first observation of a disorder-driven topological phase transition with cold atoms, and some first studies of interaction-driven effects in our synthetic momentum-space lattices.

May 8, 2017

Dr. Mary Lyon,
University of Maryland

Modeling Fusion Physics with Ultracold Neutral Plasmas

(Host: Hal Metcalf)

Plasmas comprise the vast majority of the known universe and exist over a wide range of temperatures and densities. Most plasmas form from energetic collisions between particles in a hot gas which result in the liberation of one or more electrons. However, using tools from experimental atomic physics, researchers are able to create "ultracold plasmas," which exist at temperatures close to absolute zero. Due to their large electrical potential energies and comparatively small kinetic energies, ultracold plasmas fall into a regime of plasma systems which are called “strongly coupled,” giving them properties similar to certain astrophysical systems and fusion-class plasmas. In this talk I will give an overview of the field of ultracold plasmas, provide details about some of our recent work, and show how some of this work relates to fusion physics.

July 17, 2017

Prof. Jin-Tae Kim,
Chosun University, Korea,
Yale University and University of Connecticut

Hyperfine analysis on the excited states of ultracold 85Rb-133Cs molecules via short-range photoassociation

(Host: Tom Bergeman)

Short-range photoassociation (PA), which produces continuously ultracold ^{85}Rb ^{133}Cs molecules in the lowest rovibronic ground level X ^1\Sigma^+(v=0, J=0), has opened up to investigate various hyperfine structures of deeply bound rovibrational levels in the strongly perturbed regions. Electronic states with strong singlet-triplet mixing can be useful for efficient direct molecule production in the rovibronic ground state via short-range PA. ^{85}Rb and ^{133}Cs atoms trapped in their |F_{Rb}=2> and |F_{Cs}=3> hyperfine states in dark SPOT MOTs were photoassociated into excited molecular states, which decay into the electronic ground state by spontaneous emission.
We have investigated deeply bound short-range PA lines of the  B^1\Pi(\Omega=1), c^3\Sigma^+(\Omega=0^- and 1), and b ^3|pi(\Omega=0^-,0^+, and 1) states and the 2 ^1\Pi(\Omega=1), 3 ^3\Sigma^+(\Omega=1), and 2 ^3\Pi(\Omega=1) states [1] of  85 Rb 133 Cs dissociating into the 5s(Rb) + 6p(Cs) and 6s(Cs) + 5p(Rb) limits, respectively.
Rich hyperfine structures of those electronic states with the low J which were not observed in molecular beam [2] and the FTS [3], respectively have been explained mainly considering nuclear spin-electron orbital angular momentum, Fermi-contact, and dipolar electron spin-nuclear spin interactions. Through triplet-singlet spin-orbit electronic mixings, the singlet state often has larger HFS splittings and shows HFS structure like a triplet state unexpectedly although there is no electronic spin. Analysis of the hyperfine structures makes it possible to assign  vibrational levels of singlet and triplet states which were not assigned due to strong spin-orbit interaction.
For selected PA levels, vibrational branching and rotational branching in the X ^1\Sigma^+ (v=0) state have been investigated using resonance-enhanced multiphoton ionization and depletion spectroscopy[4], respectively. Efficient production  of the rovibronic ground level X ^1\Sigma+ (v=0, J=0) has been observed for some of the PA levels. Molecule production rate up to ~1×10^4 molecules/s into the lowest rovibronic ground level has been achieved.

[1] T. Shimasaki et al., ChemPhysChem 17, 3677 (2016).
[2] Y. Lee et al., J. Phys. Chem. A 112, 7214 (2008)
[3] I. Birzniece et al., J. Chem. Phys. 138, 154304 (2013).
[4] T. Shimasaki et al., Phys. Rev. A 91, 21401 (2015).