Fall 2012 Atomic Molecular and Optical Physics Seminars at Stony Brook

All seminars are on Mondays at 4:00 PM in S-141 unless otherwise noted

August 27, 2012 Prof. Markus Oberthaler, University of Heidelberg (Germany) Atom Interferometry and Quantum Metrology (Host: Dominik Schneble)

Interferometry has proven to be one of the most sensitive measurement techniques and has found many applications in different fields of physics. In the context of atomic physics one of the paradigm applications of interferometry is Ramsey spectroscopy applied in every realization of the time standard.  A principle limit of the precision of such a device is given by the finite number of atoms involved in the interrogation. This so-called standard quantum limit can be surpassed by realizing quantum mechanically entangled input states for the interferometer - spin squeezed states. How these states can be generated and characterized in the context of Bose Einstein condensates will be discussed in detail.

September 10, 2012 Prof. A. Kumarakrishnan, York University (Canada) Interchanging the Roles of Light and Matter (Host: Dominik Schneble)

Atom interferometers that use pulses of light for coherent control of matter-wave interference can be used for wide ranging studies of light-matter interactions and for realizing precision measurements in atomic physics. We describe an echo type interferometer that utilizes a relatively simple setup to manipulate laser-cooled Rb atoms in a single ground state manifold. We review progress toward a precise determination of the atomic fine structure constant and gravitational acceleration.

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October 1, 2012 Matt Eardley, JILA Coupling Cold Atoms to a Magnetic Cantilever on an Atom Chip (Host: Harold Metcalf)

There has been much interest recently in cooling mechanical resonators to the motional ground state, using various methods. This allows one to observe quantum effects on an unprecedented large scale. Additionally, coupling these ground state resonators through various mechanisms to ultracold atoms and BEC's enables the realization of fascinating hybrid quantum systems. Because of their unique components, the properties of these hybrid systems can be observed in new and exciting ways. The well-known atom chip architecture is especially useful because standard microfabrication techniques can be used, and precise control of atom ensembles is straightforward. I will discuss our efforts to couple the magnetic spin states of ultracold atoms to a magnetic cantilever on an atom chip. Though not in the quantum domain, our experiment is represents an architecture that can be extended to create the hybrid quantum systems mentioned above.

October 22, 2012 Prof. Eden Figueroa, Stony Brook/Garching Optical Quantum Technology: Quantum Memories, Transistors and Gates (Host: Harold Metcalf)

One of the tasks of modern quantum engineering is the design of devices fulfilling the requirements to achieve operational quantum information processing and computing. These novel devices might have tasks conceptually similar to their well-known classical counterparts, but rather different physical implementation and functionality due to the intrinsically different laws governing the quantum world. In this talk I will provide an introduction on how the tool box provided by quantum mechanics can be used to create these new devices. We will explore how to combine our knowledge of solid state and atomic physics in order to create hybrid quantum memories, the possible cornerstones of future, scalable quantum networks. We will also discuss how to design and build quantum “transistors” and gates, the fundamentals constituents of a quantum processor, using two of the most powerful tools provided by quantum mechanics: electromagnetically induced transparency (EIT) and Cavity Quantum Electrodynamics (QED).

October 29, 2012 ***POSTPONED*** 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.

November 5, 2012 ***POSTPONED*** 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. Since the first generation of a dilute gas Bose-Einstein condensate (BEC) in 1995, quantum degenerate atomic gases have takenthe 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.

November 5, 2012 Dr. Ippei Danshita Yukawa Institute for Theoretical Physics, Kyoto University, Japan Critical Velocity and Anomalous Hysteresis of Dipolar Bose Gases in Optical Lattices (Host: Dominik Schneble)

The studies of ultracold dipolar bosons have been stimulated by the creation of Bose-Einstein condensates of 52Cr [1], 164Dy [2], and 168Er [3] with strong magnetic dipole-dipole interactions and gases of polar molecules [4]. In this work, we consider dipolar hardcore bosons in two-dimensional optical lattices and assume that the dipole moments are polarized to the direction perpendicular to the lattice plane, i.e., the interaction is isotropic. We focus on the two different types of lattice, namely a square lattice and a triangular lattice.  In the former case, we investigate the stability of superflow in a moving optical lattice using the linear spin-wave theory [5]. It has been predicted in previous work that there are stable supersolid (SS) phases, which possess both superfluid (SF) and crystalline orders, in dipolar hardcore bosons in a square lattice. We show that the critical velocities for the SS phases are significantly smaller than that for the SF phase. We also find that increasing the superflow can induce the phase transition from a SF to a checkerboard SS. We confirm that such a flow-induced SF-SS transition can indeed occurs during the dipole oscillation in the presence of a trapping potential [6].  In a triangular lattice, we discuss quantum phase transitions between SF, SS, and Neel solid [7]. We find that the SF-SS transition is of the first order, in contrast with previous quantum Monte Carlo simulations. We show that the SF-SS (or solid) transition can exhibit an anomalous hysteresis, in which a standard loop structure is not formed. It is found that the transition occurs unidirectionally as a consequence of the anomalous hysteresis. References: [1] A. Griesmaier et al., Phys. Rev. Lett. 94, 160401 (2005). [2] M. Lu et al., Phys. Rev. Lett. 107, 190401 (2011). [3] K. Aikawa et al., Phys. Rev. Lett 108, 210401 (2012). [4] K. Aikawa et al., Phys. Rev. Lett. 105, 203001 (2010). [5] I. Danshita and D. Yamamoto, Phys. Rev. A 82, 013645 (2010). [6] T. Saito, I. Danshita, T. Ozaki, and T. Nikuni, Phys. Rev. A 86, 023623 (2012). [7] D. Yamamoto, I. Danshita, and C. A. R. Sa de Melo, Phys. Rev. A 85, 021601

November 7, 2012 Dr. Itan Barmes, University of Amsterdam (Netherlands) "When High-Precision Spectroscopy Meets Quantum Coherent Control" (Host: Tom Weinacht)

Counter-propagating laser beams are frequently used in the field of high-precision spectroscopy where Doppler shifts are balanced in order to achieve Doppler-free excitation. The extension of this method to femtosecond pulses has been previously hampered by the small spatial overlap of counter-propagating ultrashort pulses. The single-sided (Doppler broadened) background obscures the signal and therefore results in poor signal to noise. I will discuss a novel scheme to eliminate the single-sided excitation without affecting the total counter-propagating signal. This enables direct frequency comb spectroscopy with unprecedented accuracy, demonstrated on the 5S-7S transitions in atomic rubidium. Surprisingly, this approach also enables full control over spatial excitation patterns, which adds a new dimension to the field of quantum coherent control.

November 12, 2012 Prof. Ronnie Kosloff, Hebrew University, Jerusalem (Israel) Quantum Absorption Refrigerators and  the III-Law of Thermodynamics (Host: Tom Weinacht)

Quantum thermodynamics addresses the emergence of thermodynamical laws from quantum mechanics. The III-law of thermodynamics has been mostly ignored. The unattainability version states that the absolute zero temperature cannot be reached in nite time. The dynamic version is the vanishing of rate of temperature decrease of a cooled quantum bath when T goes to 0. The III-law is then quanti ed dynamically by evaluating the characteristic exponent \xi of the cooling process: dT(t)/dt \propto T^[-xi] when approaching absolute zero, T goes to 0.      A generic continuous model of a quantum refrigerator is presented. The refrigerator is a nonlinear device merging three currents from three heat baths: a cold bath to be cooled, a hot bath as an entropy sink, and a driving bath which is the source of cooling power. A heat-driven refrigerator (absorption refrigerator) is compared to a power-driven refrigerator. When optimized, both cases lead to the same exponent xi, showing a lack of dependence on the form of the working medium and the characteristics of the drivers. The characteristic exponent is therefore determined by the properties of the cold reservoir and its interaction with the system. Two generic heat bath models are considered: a bath composed of harmonic oscillators and a bath composed of ideal Bose/Fermi gas. The restrictions on the interaction Hamiltonian imposed by the third law are discussed. [1, 2].   [1] Amikam Levy and Ronnie Koslo ff, Phys. Rev. Lett. 108, 070604 (2012).   [2] Amikam Levy, Robert Alicki, and Ronnie Koslo ff, Phys. Rev. E 85, 061126 (2012).

November 19, 2012 Prof. Hong Ling, Rowan University Superfluid pairing in a mixture of a spin-polarized Fermi gas and a dipolar condensate (Host: Hal Metcalf)

The recent experimental progress in realizing Bose-Fermi mixtures and dipolar quantum gases opened the exciting opportunity of creating dipolar Bose-Fermi mixtures with intriguing and unique properties.  In this talk, we consider a mixture of a spin-polarized Fermi gas and a dipolar Bose-Einstein condensate, where phonons can exist as low-energy density fluctuations of the dipolar condensate, and induce, between two fermions, an effective attraction, anisotropic in nature and tunable by the dipolar interaction.  We show that such an interaction can significantly increase the prospect of realizing a superfluid with a gap parameter characterized with a coherent superposition of all odd partial waves.  We formulate, in the spirit of the Hartree-Fock-Bogoliubov mean-field approach, a theory which allows us to treat calculating the critical temperature and phase separation in a unified manner. We apply this theory to estimate the critical temperature when the anisotropic Fock potential is taken into consideration and to identify the parameter space that optimizes the critical temperature before the mixture begins to phase separate.

November 26, 2012: Postponed to Feb. 11. 2013. Prof. Subhadeep Gupta, University of Washington "tba" (Host: Dominik Schneble)

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December 3, 2012 Dr. Abigail Flower, Philips Research, NY “And Now for Something Completely Different: Babies, Physics and Healthcare” (a.k.a. “An Investigation of Decelerations in the Neonatal Heart Rate”) (Host: Hal Metcalf)

The pacemaking system of the heart is complex; a healthy heart constantly integrates and responds to extracardiac signals, resulting in highly complex heart rate (HR) patterns, whereas a diseased heart may exhibit a much less complex, or very consistent, HR pattern. It is impossible at present to account for all of the factors and feedback loops affecting HR under normal conditions. However, in controlled laboratory situations, in some pathological states, or even in senescence, dynamics can show reduced complexity, which is more easily described and modeled. Reduced HR complexity can have clinical significance in that it may provide warning of impending illness, or it may provide clues about the dynamics of the heart’s pacemaking system. The HR’s of neonates are no exception to this rule; in the presence of sepsis, a bacterial infection of the bloodstream, it has been observed that the HR of an infected neonate exhibits reduced complexity in the form of reduced variability and transient decelerations. I have developed a wavelet-based detector of such HR decelerations and applied it to a large database of clinical and electrocardiographic data from infants in a neonatal intensive care unit (NICU). As a result, I have demonstrated a correlation between heart rate decelerations and the onset of neonatal sepsis. Employing this deceleration detector, it was found that decelerations may be isolated, or, more rarely, they may occur in clusters lasting up to two days. Also, within such extended clusters, it was found that sometimes during shorter sub-intervals of time, lasting up to several hours, the decelerations showed remarkable periodicity. Although demonstrations of reduced complexity of human HR during illness abound, demonstration of a reversible transition to low-dimensional, large-amplitude periodic oscillations in human cardiac rhythm has not been reported. My research documents the discovery of such transitions in the HR’s of human neonates, and presents a mathematical interpretation in the form of a noisy hard Hopf bifurcation (a common feature of many physical systems) in the neonates’ cardiac pacemaking dynamics.

December 10, 2012 Prof. Win Smith, The University of Connecticut Sympathetic Cooling of Na^+ Ions by Ultracold Na Atoms in a Hybrid Trap^* (Host: Hal Metcalf)

|Laser cooling atoms to ultracold temperatures has opened a fruitful regime for atomic physics. Closed-shell atomic ions, such as Na+, and nearly all molecular ions lack the optical transitions from the ground state that are required for laser cooling, restricting their use in a variety of experiments: near zero-K reaction studies, cold ion spectroscopy and quantum gates. We have created a hybrid atom-ion trap system to study cooling and reactions of atomic and molecular ions which cannot readily be laser cooled. It consists of a magneto-optical trap (MOT) for Na, concentric with a linear Paul r.f. ion trap. Recent simulations we have carried out using SIMION [PRA 86, 033408 (2012)] show that cold MOT atoms may be used to sympathetically cool trapped hot atomic or molecular ions to sub-Kelvin temperatures. We found experimental evidence of this: trapped Na+ ions exposed to equal mass Na MOT atoms have extended lifetimes when MOT-refrigerated in the Paul trap. Unwanted ions (e.g. Na2^+ from associative ionization in the MOT) may be selectively quenched with minimal disturbance of the trapped Na^+ions. Initial surprising experiments with Ca^+ ions interacting with the Na MOT will be mentioned also. &#61623 Supported by NSF under grant PHY-0855570. &#61623 In collaboration with Ila Sivarajah, Douglas Goodman, James E. Wells (UConn) and Frank Narducci (Naval Air Systems Command, Pawtuxent River, MD 20670). &#61623 A preprint giving the experimental results and references can be found at arXiv:1209.2106v2 [physics.atom-ph] (submitted to PRA).