Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G29: Focus Session: Artificial Gauge Fields and Systems with Long Range Interactions I 
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Sponsoring Units: DAMOP Chair: Victor Galitski, University of Maryland at College Park Room: 603 
Tuesday, March 4, 2014 11:15AM  11:27AM 
G29.00001: Spin Waves and Dielectric Softening of Polar Molecule Condensates Brandon Peden, Ryan Wilson, Charles Clark, Seth Rittenhouse We consider an oblate BoseEinstein condensate of heteronuclear polar molecules in a weak applied electric field. This system supports a rich quasiparticle spectrum that plays a critical role in determining its bulk dielectric properties. In particular, in sufficiently weak fields, the system undergoes a polarization wave rotonization, leading to the development of textured electronic structure and a dielectric instability that is characteristic of the onset of a negative static dielectric function. [Preview Abstract] 
Tuesday, March 4, 2014 11:27AM  11:39AM 
G29.00002: Measuring dipolar spin exchanges in ultracold polar KRb molecules Steven Moses, Bo Yan, Bryce Gadway, Jacob Covey, Kaden Hazzard, Ana Maria Rey, Deborah Jin, Jun Ye By encoding spin in rotational states, we have observed spin exchanges of ultracold polar KRb molecules that are confined in a deep three dimensional optical lattice [Yan \textit{et al.}, Nature \textbf{501}, 521 (2013)]. The interactions manifest as a density dependent decay of the spin coherence of the system, which is probed via Ramsey spectroscopy. In addition to decaying, there are oscillations in the contrast, with frequency components that are consistent with the dipolar interaction energies. By adding additional pulses, we can suppress pairwise dipolar interactions. We have studied these spin exchanges for two different pairs of rotational states, which differ by a factor of two in interaction strength, and find the decay and oscillations to be roughly twice as fast in the case of stronger interactions. This work lays the foundation for future studies of quantum magnetism with polar molecules in optical lattices. [Preview Abstract] 
Tuesday, March 4, 2014 11:39AM  11:51AM 
G29.00003: New tools for farfromequilibrium quantum spin dynamics inspired by ultracold molecule experiments Kaden Hazzard, Michael FossFeig, Bryce Gadway, Bo Yan, Steven Moses, Jacob Covey, Deborah Jin, Jun Ye, Ana Maria Rey We describe new numerical techniques based on a type of cluster expansion and analytic solutions for treating farfromequilibrium dynamics in quantum manybody spin models. Specifically, we apply them to dynamics following a quantum quench that is routinely implemented in experiments with Ramsey spectroscopy. For many observables, these new approaches converge extremely rapidly compared to existing techniques, which are unable to converge using any feasible computational resources. We describe the theoretical methods and our understanding of their superior convergence. These calculations are motivated by recent experiments with ultracold molecules in optical lattices [ Yan \textit{et al.}, Nature \textbf{501}, 521 (2013) ] and trapped ions [ Britton \textit{et al.}, Nature \textbf{484}, 489 (2012) ], which are described by spin models with longrange interactions in appropriate limits. We will compare theoretical predictions with experimental observations in these systems. We expect the novel methods developed to describe ultracold matter to also have applications to solid state systems, for example in the dynamics of nitrogenvacancy centers in diamond or energy transfer in complicated molecules. [Preview Abstract] 
Tuesday, March 4, 2014 11:51AM  12:27PM 
G29.00004: Dipolar interactions of latticeconfined polar molecules Invited Speaker: Deborah Jin Longrange dipolar interactions can be used to realize lattice spin models for exploring quantum magnetism. I will discuss experiments where we observe dipolar spinexchange interactions for ultracold KRb molecules confined in a deep threedimensional optical lattice. The longrange dipolar interactions exist even in the absence of tunneling and extend beyond nearest neighbors. This enables coherent spin dynamics even for gases with relatively low lattice filling. [Preview Abstract] 
Tuesday, March 4, 2014 12:27PM  12:39PM 
G29.00005: Propagation of information in longrange interacting lattice systems ZheXuan Gong, Michael FossFeig, Spyridon Michalakis, Alexey V. Gorshkov Propagation of information in shortrange interacting lattice systems is restricted to within a linear ``light cone,'' as demonstrated by the wellknown LiebRobinson bound, thus ensuring a well defined notion of maximum propagation velocity. Whether longranged interactions can lead to a different shape of this light cone, and the divergence of the associated velocity, is an important but largely unexplored question. We prove that for a wide class of longrange interacting lattice systems, a linear light cone still exists for certain regions of space and time, and for some experimentally relevant classes of models this linear light cone persists in the entire spacetime. We then give counterexamples showing that, for wellengineered lattice system, long range interactions can indeed give rise to a sublinear ``light cone,'' and thus a divergent speed of information propagation. [Preview Abstract] 
Tuesday, March 4, 2014 12:39PM  12:51PM 
G29.00006: Generation of manybody entanglement in longrange interacting systems Michael FossFeig, ZheXuan Gong, Alexey Gorshkov, Charles Clark The existence of longranged interactions generally complicates the description of manybody systems. However, in the limit where the interactions become infinitely longrangedi.e. independent of distancethe emergence of extra conserved quantities typically makes the behavior quite simple. Such infiniteranged interactions are often assumed in the description of experiments aiming to produce large scale entangled states, for instance via spinsqueezing, but of course ``infinite'' in this context is an idealization. We consider the generation of entanglement in Ising models with long (but not infinite) ranged interactions, which are relevant to the description of a variety of quantum information/simulation platforms including trapped ions, polar molecules, Rydberg atoms, and nitrogen vacancy centers in diamond. We demonstrate that there exists a notion of sufficiently longranged interactions, for which the scaling of entanglement with system size expected from the infiniterange idealization is completely unmodified. Our results have direct applications to experimental protocols aiming to achieve quantumenhanced metrology. [Preview Abstract] 
Tuesday, March 4, 2014 12:51PM  1:03PM 
G29.00007: Spin dynamics and entanglement growth with trapped ions, atoms \& molecules Johannes Schachenmayer, Ben Lanyon, Christian Roos, Andrew Daley, Bihui Zhu, Ana Maria Rey Trapped ions and systems of cold atoms or molecules in optical lattices offer controlled environments to experimentally study nonequilibrium dynamics of manybody quantum spinmodels with interactions of varying range. Theoretically calculating dynamics of observables for these experiments is a major challenge both analytically and numerically. In 1D, the growth behavior of the entanglement entropy between different blocks of a manybody state determines whether the evolution of the system can be efficiently simulated on a classical computer or not. In return, the study of entanglement growth can guide experiments to regimes where a quantum simulator can outperform a numerical simulation. Here we present results on the entanglement growth behavior in 1D strings of ions after a quench, and show how the growth depends on the range of the interactions. Furthermore we report on progress on methods for higher dimensional systems. These can be used to model Ramseydynamics for current experiments with alkaline earth atoms or polar molecules in optical lattices, or for systems with Rydberg atoms. [Preview Abstract] 
Tuesday, March 4, 2014 1:03PM  1:15PM 
G29.00008: Engineered longrange interactions on a 2D array of trapped ions Joseph W. Britton, Brian C. Sawyer, John J. Bollinger, James K. Freericks Ising interactions are one paradigm used to model quantum magnetism in condensed matter systems. At NIST Boulder we confine and Doppler laser cool hundreds of $^9$Be$^+$ ions in a Penning trap. The valence electron of each ion behaves as an ideal spin1/2 particle and, in the limit of weak radial confinement relative to axial confinement, the ions naturally form a twodimensional triangular lattice. A variablerange antiferromagnetic Ising interaction is engineered with a spindependent optical dipole force (ODF) through spindependent excitation of collective modes of ion motion. We have also exploited this spindependent force to perform spectroscopy and thermometry of the normal modes of the trapped ion crystal. The high spincount and longrange spinspin couplings achievable in the NIST Penning trap brings within reach simulation of computationally intractable problems in quantum magnetism. Examples include modeling quantum magnetic phase transitions and propagation of spin correlations resulting from a quantum quench. The Penning system may also be amenable to observation of spinliquid behavior thought to arise in systems where the underlying lattice structure can frustrate longrange ordering. [Preview Abstract] 
Tuesday, March 4, 2014 1:15PM  1:27PM 
G29.00009: Effects of the anisotropic dipoledipole interaction in fewparticle quantum systems Gunnar Eriksson, Jonas C. Cremon, Stephanie M. Reimann Recent realizations of condensates of atoms with large magnetic dipole moments, ultracold gases of dipolar molecules and Rydberg atoms have made it possible to study systems with a long range and spatially anisotropic interaction. These special properties of the interaction is presumed to give rise to new and exotic phases and other manybody phenomena and they can be altered by changing the direction of the dipoles with e.g. an external field. For ultracold gases there is now also the possibility to access the fewparticle regime. Combining these techniques, fewparticle systems with the dipoledipole interaction, resembling e.g. electrons in a quantum dot or nucleons in a nuclei, could be studied. We have performed exact diagonalization to systems of a few fermions interacting with the dipoledipole interaction in a quasi2D system. For such a system under rotation, the anisotropy of the interaction can be used to reveal the vortex structure in the particle density and the probability current (Phys. Rev. A 86, 043607). The anisotropy also allows the system to reduce the interaction energy by more exotic particle arrangements, which leads to new behavior that can be externally tuned. [Preview Abstract] 
Tuesday, March 4, 2014 1:27PM  1:39PM 
G29.00010: Effective mass and superfluid fraction in a periodic ultracold Bose gas with longrange interaction CheHsiu Hsueh, YuChing Tsai, WenChin Wu The scheme that superfluid fraction $f_s=\rho_s/\rho$ is equal to the ratio of bare to effective mass $m/m^*$ of the particles is applied to investigate the superfluidsupersolid (SFSS) transition in a periodic ultracold Bose gas with longrange interaction. We consider both the Rydbergdressed Bose gas with tunable blockade radius and coupling constant and the dipolar Bose gas with controllable coupling constant and polarization. Both the strong and week lattice limits are investigated. [Preview Abstract] 
Tuesday, March 4, 2014 1:39PM  1:51PM 
G29.00011: Strongly interacting photons Mohammad Maghrebi, Ofer Firstenberg, Alexey Gorshkov We develop a quantum theory of light strongly interacting via longrange RydbergRydberg interactions within the framework of the electromagnetically induced transparency. We elaborate on the interaction between photons, and discuss attractive as well as repulsive regimes. Specifically, we find solitonic bound states of photons, and explain their propagation inside the medium. Finally, we discuss the possibilities of manybody phases of strongly interacting light. [Preview Abstract] 

G29.00012: ABSTRACT WITHDRAWN 
Tuesday, March 4, 2014 2:03PM  2:15PM 
G29.00013: Cavity Optomechanics with synthetic Landau levels of ultra cold Fermi gas Sankalpa Ghosh, Bikash Padhi Ultra cold fermionic atoms placed in a synthetic magnetic field arrange themselves in Landau levels. We theoretically study the optomechanical interaction between the light field and collective excitations of such fermionic atoms in synthetic magnetic field by placing them in side a Fabry Perot cavity. We derive the effective hamiltonian for particle hole excitations from a filled Landau level using a bosonization technique and obtain an expression for the cavity transmission spectrum. Using this we show that the cavity transmission spectrum demonstrates cold atom analogue of Subnikov de Hass oscillation in electronic condensed matter systems. We discuss the experimental consequences for this oscillation for such system and the related optical bistability. Ref. Bikash Padhi and Sankalpa Ghosh, Physical Review Letters, Vol 111, 043603 (2013) [Preview Abstract] 
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