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 2013

 January 25, 2013, 3:00 PM Michael Bellos, University of Connecticut Optical production of  Ultracold Rb2 molecules in states with a magnetic or electric dipole moment (Host: Dominik Schneble)

 I would like to review different ways for forming molecules out of  ultracold atoms, with an emphasis on photoassociation. Photoassociation is the process of converting two atoms and a photon into a bound molecule. I will touch on photoassociation at short range and photoassociation into resonantly-coupled levels as two ways of forming deeply-bound molecules. Finally, I will describe recent work on "butterfly" states---a class of excited states with a large electric dipole moment---that result from a novel form of chemical binding.

 February 4, 2013 Prof. Peter Engels, Washington State University New trends in BEC hydrodynamics: novel types of solitons and dispersion engineering (Host: Dominik Schneble)

 The peculiar dynamics of superfluids are a fascinating researchtopic. Sincethe first generation of a dilute gas Bose-Einstein condensate (BEC) in 1995, quantum degenerate atomic gases have taken the investigation of quantum hydrodynamics to a new level. The atomic physics toolbox has grown tremendously and now provides unique and powerful ways to explore nonlinear quantum systems.     As an example, pioneering results have recently revealed that the counterflow between two superfluids can be used as a well controlled tool to access the rich dynamics of vector systems. New structures, such as beating dark-dark solitons which only exist in multicomponent systems and have never been observed before, can now be realized in the lab for the first time. Furthermore, the field of nonlinear quantum hydrodynamics is entering new regimes by exploiting Raman dressing as a tool to directly modify the dispersion relation. This leads to the generation of spin-orbit coupled BECs, artificial gauge fields, etc. that are currently receiving tremendous interest due to their parallels to complex condensed-matter systems.     In this talk I will present the recent and ongoing experiments at WSU that focus on novel types of solitons as well as Raman-dressed BECs.

 February 11, 2013 Prof. Subhadeep Gupta, University of Washington Quantum Mixtures of Alkali and Alkaline-Earth-Like Atoms (Host: Dominik Schneble)

 We have produced quantum degenerate mixtures of ytterbium (Yb) and lithium (Li) atoms. Such a mass-mismatched mixture can be useful for various studies in few- and many-body physics. Furthermore, this combination (of an alkaline-earth-like and an alkali atom) also forms the starting point for the production of ultracold paramagnetic polar molecules, with proposed applications in quantum simulation, quantum information science, and precision tests of fundamental physics. In addition to our production procedures, I will also report on our study of the collisional stability of the Yb-Li mixture in the vicinity of a Li Feshbach resonance. In our experiment, Yb can be prepared as either a bath for or a probe of the strongly interacting Li Fermi gas.  I will also discuss the prospects for tunable inter-species interactions and the YbLi molecule.

 February 25, 2013 Prof. Doerte Blume, Washington State University S-Wave Interacting Fermions Under Anisotropic Harmonic Confinement: Dimensional Crossover of Energetics and Virial Coefficients (Host: Tom Bergeman)

 Few-body physics has played a prominent role in atomic, molecular, chemical and nuclear physics since the early days of quantum mechanics. It is now possible---thanks to tremendous progress in cooling, trapping, and manipulating ultracold samples---to experimentally study few-body phenomena in trapped atomic and molecular systems with unprecedented control. This talk summarizes recent studies of few-body phenomena in trapped fermionic gases. We present essentially exact solutions of the Schrodinger equation for three equal-mass fermions in two different spin states with zero-range s-wave interactions and discuss the transition from quasi-one-dimensional to strictly one-dimensional and quasi-two-dimensional to strictly two-dimensional geometries. We determine and interpret the eigenenergies of the system as a function of the trap geometry and the strength of the s-wave interactions. The eigenenergies are used to investigate the dependence of the second- and third-order virial coefficients, which play an important role in the virial expansion of the thermodynamic potential, on the geometry of the trap. We show that the second- and third-order virial coefficients for aniostropic confinement geometries are, for experimentally relevant temperatures, very well approximated by those for the spherically symmetric confinement for all s-wave scattering lengths.

 March 4, 2013 Dr. Denys Bondar, Princeton University To commute or not to commute, that is everyting to know about classical and quantum mechanics (Host: Tom Weinacht)

 We introduce Operational Dynamic Modeling (ODM) as  asystematic theoretical framework for deducing equations ofmotion from the evolution of observed average values. Then, it is demonstrated that ODM is capable of deriving wide ranging dynamics including classical and quantum mechanics.

 April 1, 2013 Anita Madan and Michael Hatzistergos, IBM Science in the Semiconductor Industry - Perspectives and Challenges (Host: Hal Metcalf)

 With the continuing demand for faster chips,  chips get smaller and smaller.  There are accompanying challenges in their characterization. State of the art techniques are needed. Our talk will focus on two of the cutting edge characterization techniques used in our industry - X-ray techniques for characterizing strain and Atom Probe Tomography for determining the positions of the atoms. We will also describe how skills acquired as science undergraduates as well as in graduate school have been helpful in our current jobs.

 April 8, 2013 Prof. Maxim Olshanii, University of Massachusetts at Boston Geometry of Quantum Observables, Integrability-Thermalizability Transition, and Extended Thermodynamics of Integrable and/or Mesoscopic Systems (Host: Tom Bergeman)

 The concept of ergodicity—--the convergence of the temporal averages of observables to their ensemble averages---is the cornerstone of thermodynamics. The transition from a predictable, integrable behavior to ergodicity is one of the most difficult physical phenomena to treat; the celebrated KAM theorem is the prime example. This talk is founded on the observation that for many classical and quantum observables, the sum of the ensemble variance of the temporal average and the ensemble average of temporal variance remains approximately constant across the integrability-ergodicity transition. We show that this property induces a particular geometry of quantum observables—--Frobenius-Hilbert-Schmidt one—--that naturally encodes all the phenomena associated with the emergence of ergodicity: the Eigenstate Thermalization effect, the decrease in the inverse participation ratio, and the disappearance of the integrals of motion. As an application, we use this geometry to solve a known problem of optimization of the set of conserved quantities---coming from symmetries or from finite-size effects, regardless---to be incorporated in an extended thermodynamical theory of integrable, near-integrable, or mesoscopic systems.

 April 15, 2013 Dr. Xijie Wang, Brookhaven National Laboratory Filling the Ultrafast Gaps: FEL, THz and UED R&D at BNL Source Development Laboratory (Host: Tom Weinacht)

 Synchrotron radiation sciences have witnessed an explosive growth in the last few decades thanks to the advance in the electron storage ring and insertion device technologies, leading a drastic increase in the x-ray brightness. Advance in laser technology has been similarly spectacular: pulse compression technique giving rise to femtosecond terawatts pulses and high-harmonic generation technique for shorter wavelength coverage have opened up new frontiers in laser spectroscopy and dynamics studies.   But there are still significant gaps in our scientific toolbox,  such as simultaneous having atomic spatial and temporal resolution (ultrafast gap); high power THz source (THz gap).  Free electron laser (FEL) and Ultrafast Electron diffraction (UED) are two most important technologies for filling the ultrafast gap, and coherent radiation from high-brightness electron beam has demonstrated the potential for high power THz generation. Source Development Laboratory (SDL) at Brookhaven National Laboratory  (BNL) has made critical contributions filling the ultrafast and THz gaps. After a brief introduction on FEL physics, I will discuss some exciting FEL, THz and UED experimental results this talk.

 April 22, 2013 Prof. Long Cai California Institute of Technology Single cell analysis by super-resolution barcoding (Host: Hal Metcalf)

 Fluorescence microscopy is a powerful quantitative tool for exploring regulatory networks in singl cells.  However, the number of molecular species that can be measured simultaneously is limited by the spectral separability of fluorophores.  Here we demonstrate a simple but general strategy to drastically increase the capacity for multiplex detection of molecules in single cells by using optical super-resolution microscopy (SRM) and combinatorial labeling.  The basis for this new approach are the following: given the 10 nanometers resolution of a super-resolution microscope and a typical cell a size of (10um)3, individual cells contains effectively 109 super-resolution pixels or bits of information.  Most eukaryotic cells have 104 genes and cellular abundances of 10-100 copies per transcript.  Thus, under a super-resolution microscope, an individual cell has 1000 times more pixel volume or information capacities than is needed to encode all transcripts within that cell.  As a proof of principle, we labeled mRNAs with unique combinations of fluorophores using Fluorescence in situ Hybridization (FISH), and resolved the sequences and combinations of fluorophores with SRM.   We measured the mRNA levels of 32 genes simultaneously in single yeast cells.  These experiments demonstrate that combinatorial labeling and super-resolution imaging of single cells provides a natural approach to bring systems level analysis into single cells.

 April 23, 2013 (P&A COLLOQIUM) Prof. Jun Ye, JILA / UC Boulder Ultracold Molecules - New Frontiers in Quantum & Chemical Physics (Host: Dominik Schneble)

 Molecules cooled to ultralow temperatures provide fundamental new insights to molecular interaction dynamics in the quantum regime. In recent years, researchers from various scientific disciplines such as atomic, optical, and condensed matter physics, physical chemistry, and quantum science have started working together to explore many emergent research topics related to cold molecules, including cold chemistry, strongly correlated quantum systems, novel quantum phases, and precision measurement. Complete control of molecular interactions by producing a molecular gas at very low entropy and near absolute zero has long been hindered by their complex energy level structure. We have recently developed a number of technical tools to laser cool and magneto-optically trap polar molecules, as well as to cool molecules via evaporation. Another recent experiment has brought polar molecules into the quantum regime, in which ultracold molecular collisions and chemical reactions must be described fully quantum mechanically. We control chemical reaction via quantum statistics of the molecules, along with their long-range and anisotropic dipolar interactions. Further, molecules can be confined in reduced spatial dimensions and their interactions are precisely manipulated via external electric fields. Those efforts have started to yield observations on strongly interacting and collective quantum effects in an ultracold gas of molecules.

 April 29, 2013 Dr. Xi Xing, Princeton University Optimal Control over a Homologous Chemical Series (Host: Tom Weinacht)

 Optimal control experiments can readily identify effective shaped fs laser pulses, or "photonic reagents", that achieve a wide variety of objectives.   This talk will focus on the studies of control fragmentation with a series of homologous molecules (halomethanes containing two or three halogen atoms), where the control objectives are to maximize the ratios of halogen over methyl halogen fragment ions upon dissociative ionization.  I will show that effective controls can be achieved with reduced dimensionality in control parameters; the optimal photonic reagents identified from each molecule show systematic trends in objective yield when cross applied to analogous molecules; the prescription of photonic reagents can be successfully transferred from one lab to another.  These results provide a basis to expect chemical responses from photonic reagents in analogy to the action of traditional chemical reagents.

 April 30, 2013 (P&A COLLOQIUM) Prof. Randall G Hulet, Rice University Quantum Simulation with Atoms in Optical Lattices (Host: Dominik Schneble)

 Some of the most complex and vexing problems in electronic materials are modeled by extremely simple Hamiltonians. High-temperature superconductors, for example, may arise from magnetic interactions in a Mott insulating state, described by the simple Hubbard model. The Hubbard model stipulates that particles (electrons in the case of superconductors) are distributed in a square lattice where they can hop from site to site with a tunneling energy t, and where they may interact with occupied nearest neighbor sites with interaction energy U. No one knows whether this simple “hydrogen-atom” model actually gives rise to the d-wave pairing underlying the cuprate superconductors, as the model, while simple to describe, is not solvable using digital computers. I will discuss two experiments that use ultracold atoms in an optical lattice as stand-ins for the electrons in ionic lattices: 1) the Hubbard model in 3D; and 2) the polarized spin-½ Fermi gas in 1D. In the first experiment, we are searching for the anti-ferromagnetic Mott insulating state that is expected to exist above the superconducting transition when there is exactly one-atom per lattice site. We have used Bragg scattering of near-resonant light to characterize the lattice, and will use a spin-sensitive variant of this tool to detect magnetic correlations. In the second experiment, we have used an optical lattice in two-dimensions to create a bundle of 1D tubes containing an imbalanced two spin-state mixture of 6Li fermions. The phase diagram of this system contains three phases: a fully-paired superfluid, a fully-polarized ferromagnet, and a partially polarized state that is predicted to be the exotic FFLO superfluid state, for which the pairs have non-zero center of mass momentum.

 May 6, 2013 Dr. Melanie Roberts, Stony Brook University High-Resolution Direct-Absorption Spectroscopy of Supersonically-Cooled Radicals in the Mid-Infrared Region (Host: Tom Allison)

 The energy of the mid-infrared region generally corresponds to the amount of energy required to excite bond-stretching vibrations in molecules. Using the technique of high-resolution direct-absorption spectroscopy we obtain the energy levels of vibration, rotation, and occasionally nuclear fine and hyperfine interactions in molecules in order to learn about bonding and structure of the molecule. This talk will focus on absorption spectroscopy of highly-reactive radicals important in combustion chemistry. Absorption spectra were recorded using a widely tunable, narrow linewidth (<1 MHz), cw mid-infrared spectrometer capable of determining and reproducing frequencies to three parts in 108 with absorption noise levels at or near the shot noise limit. To generate the highly reactive and short lived radicals, a discharge breaks apart a stable precursor molecule. The discharge is localized at the orifice of a slit supersonic expansion, which cools the radicals to around 20 K and allows for sub-Doppler spectral resolution.  By way of example, the two fundamental CH stretches in CH2D are studied with full rotational resolution for the first time. The narrow linewidths (50-100 MHz) of the transitions reveal resolved fine structure and partially resolved hyperfine structure. In addition to the experimental efforts on CH2D, we developed the first model capable of simultaneously describing the CH and CD stretches of all the hydrogenic isotopomers of methyl radical.

 May 7, 2013, 10:30am Michael Schecter, University of Minnesota Dynamics of mobile impurities in one-dimensional quantum liquids (Host: Dominik Schneble)

 The study of dissipationless flow is an active field which continues to fascinate researchers. Impurity motion through a one-dimensional (1D) superfluid is one example which has brought several surprises. Even for weak coupling, the single-impurity dispersion relation is strongly renormalized when the momentum approaches $\pm\pi\hbar n$, where $n$ is the fluid density. At yet larger momentum, one finds that the dispersion relation is actually transformed into a \emph{periodic} function, with period $2\pi\hbar n$. We show that this remarkable feature leads to Bloch oscillations of a driven impurity for a large range of temperatures and external drives.  -- We also find that for sufficiently heavy impurities the dispersion develops non-analytic cusps at momenta $j\pi\hbar n$ where $j$ is an odd integer. Such cusps are accompanied by metastable upper branches which have dramatic consequences for impurity motion, including the divergence of the zero-temperature, non-linear mobility.  -- For a dilute concentration of impurities, one typically regards the latter as non-interacting and independent. However, in 1D even weakly interacting quasi-particles tend to be unstable against the formation of collective excitations. Thus, even for the case of non-interacting impurities, one should consider the possibility of emergent impurity interactions arising from mutual coupling to one and the same fluid. We find that the massless and quantum nature of low-energy fluid fluctuations mediates a universal inter-impurity potential scaling as the inverse cube of the separation.

 June 10, 2013, 4:00 PM Dr. Stephan Ritter Max Planck Institute for Quantum Optics (Germany) An Elementary Quantum Newtwork of Single Atoms in Optical Cavities (Host: Eden Figueroa)

 Quantum networks form the basis of distributed quantum computing architectures and quantum communication. Single atoms in optical cavities are ideally suited as universal quantum network nodes capable of sending, storing and retrieving quantum information. We demonstrate this by presenting an elementary version of a quantum network based on two identical nodes in remote, independent laboratories. The reversible exchange of quantum  information and the creation of remote entanglement are achieved by exchange of a single photon. The dynamic control of coherent dark states allows for the generation of a single photon in one system, which is subsequently stored at the other node. A heralded alternative to the direct state transfer is provided by teleportation, which we implement using a time-resolved photonic Bell-state measurement based on two-photon quantum inference. Quantum control over all degrees of freedom of the single atoms and our cavity-based approach to quantum networking offer a clear perspective for scalability.

 June 12, 2013, 11:00 AM Dr. Sotir Chervenkov Max Planck Institute for Quantum Optics (Germany) A Roadmap for Production of Ultracold Polyatomic Polar Molecules (Host: Eden Figueroa)

 Producing ensembles of polyatomic molecules at ultracold temperatures is a challenge. In pursuit of this goal, we propose a very general scheme combining sequentially three promising techniques. First, high-flux continuous supersonic beams of internally cold polar molecules are produced from a buffer-gas cell [1, 2] operated in the hydrodynamic regime. Then those beams are guided in an electrostatic guide [3] and decelerated by the centrifugal potential in a rotating frame. The decelerated continuous beams are delivered to an electrostatic trap, where the molecules are further cooled down via a Sisyphus process [4] employing laser, microwave, and radiofrequency radiation. Here we demonstrate experimental results from the three techniques and give evidence for the viability of their joint operation en route to achieving sub-milliKelvin ensembles of polyatomic polar molecules. [1] L. D. van Buuren et al., Phys. Rev. Lett. 102, 033001 (2009) [2] C. Sommer et al., Faraday Discuss. 142, 203 (2009) [3] S. A. Rangwala et al., Phys. Rev. A 67, 043406 (2003) [4] M. Zeppenfeld et al., Nature 491, 570 (2012)

last updated 04/24/2013