Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F24: Quantum Gases in Optical LatticesFocus

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Sponsoring Units: DAMOP Chair: Ulrich Schneider, Cambridge University Room: BCEC 159 
Tuesday, March 5, 2019 11:15AM  11:27AM 
F24.00001: Microscopic studies of doped coldatom FermiHubbard antiferromagnets Christie S Chiu, Geoffrey Ji, Annabelle Bohrdt, Muqing Xu, Justus Brüggenjürgen, Michael Knap, Eugene Demler, Fabian Grusdt, Markus Greiner, Daniel Greif The experimental platform of ultracold fermionic atoms in optical lattices offers new perspectives for studying the physics of strongly correlated materials. We use this platform to implement the FermiHubbard model, a paradigmatic model thought to capture the physics of hightemperature superconductivity, the pseudogap, and other phenomena containing longstanding open questions. The additional tool of quantum gas microscopy enables siteresolved readout and access to projections of the manybody wavefunction in the Fock basis. I will report on our most recent studies of doped antiferromagnets, where there is no universally agreedupon mechanism for the interplay between hole motion and antiferromagnetic order. 
Tuesday, March 5, 2019 11:27AM  11:39AM 
F24.00002: Toward lowentropy states in the FermiHubbard model with quantum gas microscopy Muqing Xu, Christie S Chiu, Geoffrey Ji, Justus Brüggenjürgen, Anton Mazurenko, Maxwell F Parsons, Marton KanaszNagy, Richard Schmidt, Fabian Grusdt, Eugene Demler, Daniel Greif, Markus Greiner Ultracold atoms in optical lattices are a powerful platform for studying strongly correlated quantum systems. We study the repulsive FermiHubbard model through quantum gas microscopy with fermionic Lithium6 atoms in a square lattice. This technique allows for singlesite resolved readout and manipulation, and has enabled us to achieve longrange antiferromagnetic order across our entire sample by performing entropy redistribution. Accessing intriguing phases in the FermiHubbard model, requires development of new techniques for lowentropy quantum state preparation. Here we report on our lownoise interfering optical lattice, which offers dynamically tunable lattice geometry and allows for studies of the FermiHubbard model in dimerized, honeycomb, and triangular lattices. This tunability can alternatively facilitate an adiabatic ramp from an ultralow entropy initial state, prepared through entropy redistribution, toward stronglycorrelated quantum phases. Another possible application of this interfering lattice is to provide simultaneous readout of both spin species. 
Tuesday, March 5, 2019 11:39AM  11:51AM 
F24.00003: Photoemission spectroscopy of a FermiHubbard system with a quantum gas microscope Peter T. Brown, Elmer GuardadoSanchez, Waseem S Bakr Strongly correlated systems with superconducting ground states, including the hightemperature superconducting cuprates and the unitary fermi gas, exhibit normal state precursors to the superconducting gap in their singleparticle excitations. A quantitative understanding of these so called pseudogap regimes may elucidate details of the ground states, but developing this is difficult in real materials because the parameters of the microscopic Hamiltonian are not known. In cold atom experiments the development of fermionic quantum gas microscopes has enabled highprecision studies of fermions in optical lattices. The Hamiltonian parameters of these systems can be calculated from first principles, and good agreement between theory and experiment has been reported in recent studies of equaltime spin and density correlations. In this talk I will report on the development of angleresolved photoemission spectroscopy (ARPES) compatible with quantum gas microscopy and its application to studying pseudogap physics in an attractive FermiHubbard system across the BECBCS crossover, setting the stage for future studies of the pseudogap regime in repulsive Hubbard systems. 
Tuesday, March 5, 2019 11:51AM  12:03PM 
F24.00004: Progress toward a dipolar quantum gas microscope with an expandable lattice Anne Hebert, Gregory Phelps, Aaron Krahn, Furkan Ozturk, Markus Greiner

Tuesday, March 5, 2019 12:03PM  12:15PM 
F24.00005: Progress toward an Erbium Dipolar Quantum Gas Microscope Gregory Phelps, Anne Hebert, Aaron Krahn, S.Furkan Ozturk, Markus Greiner Quantum gas microscopy provides an exciting platform for the study of in situ atomatom interactions. Recent advances in quantum gas microscopy have allowed probing of the BoseHubbard and FermiHubbard Hamiltonian. We are currently extending these platforms with the introduction of an Erbium Dipolar Quantum Gas Microscope allowing us to study dipoledipole interactions in a lattice. Erbium has several exciting properties, which increase the control and flexibility of these systems. These include stable bosonic and fermionic isotopes, a large magnetic dipole moment (7uB), a large spin value (J=6 and F=19/2 for bosonic and fermionic isotopes), a rich Feshbach spectrum, and several broad and narrow atomic transitions. Here we are presenting our recent progress toward an Erbium Quantum Gas Microscope. This features the integration of several unique systems, such as a highresolution reflective objective, an accordion lattice for imaging, and a low disorder optical lattice. These developments will allow us to benefit from the longrange interaction of Erbium and probe the Extended BoseHubbard and Extended FermiHubbard Hamiltonian to an unprecedented degree. 
Tuesday, March 5, 2019 12:15PM  12:27PM 
F24.00006: Antiferromagnetic Order and NonEquilibrium Distributions in the FloquetEngineered Hubbard Model Nicklas Walldorf, Dante Kennes, Jens Paaske, Andrew Millis The periodically driven halffilled twodimensional Hubbard model is studied via a saddle point plus fluctuations analysis of the Keldysh action. The drive is implemented as an alternating electric field, and the system is coupled to a metallic substrate in thermal equilibrium to allow for a nonequilibrium steady state synchronized to the drive. For drive frequencies below the equilibrium gap, and strong enough drive amplitudes, the meanfield equation has multiple solutions with a substantial timedependent component. Even for "Magnus" drive frequencies much larger than the equilibrium gap, a oneloop analysis around the meanfield solution shows that even if no real electronhole pairs are excited, the ac drive produces a highly excited, generically nonthermal distribution of fluctuations, which can affect the physics significantly, for example destroying zerotemperature longranged antiferromagnetic order for large enough drive amplitudes. 
Tuesday, March 5, 2019 12:27PM  12:39PM 
F24.00007: Strong correlations in magicangle semimetals Justin Wilson, Yixing Fu, Elio Koenig, YangZhi Chou, Jed Pixley In magicangle graphene, Moiré patterns lead to an enlarged unit cell, miniBrillouin zone, and strongly correlated phases (as shown experimentally). We generalize this behavior to a whole class of semimetallic models from one to threedimensions, and we show that the key ingredients are (1) an “untwisted” semimetallic band structure and (2) a spatially quasiperiodic structure (e.g., a “twist”) [1]. As the quasiperiodic structure is enhanced, the velocity of the effective lowenergy semimetal decreases until it vanishes at a quantum phase transition. The magicangle phenomena are associated with this eigenstate phase transition which is a unique type of “Anderson delocalization” transition in momentum space. Further, it is accompanied with flatbands and behaves universally across models. Lastly, we build effective Hubbard models on the new bands by computing Wannier states. The interactions in these Hubbard models are strongly enhanced at this transition, indicating the existence of strongly correlated phases. All ingredients to realize our proposal are available in presentday coldatomic laboratories for which the magicangle effect can be exploited to induce strong correlations in quantum degenerate gases. 
Tuesday, March 5, 2019 12:39PM  12:51PM 
F24.00008: Enhancement and destruction of superfluidity: Unusual effects of population imbalance of atomic Fermi gases on a 1D optical lattice Qijin Chen, Jibiao Wang We study the superfluid behavior of population imbalanced ultracold atomic Fermi gases with a short range attractive interaction on a 1D optical lattice, using a pairing fluctuation theory. Due to the latticecontinuum mixing in a 1D optical lattice, population imbalance now has highly unusual effects. While the transition Tc in the balanced case decreases and scales as k_{F}a in the BEC regime, it approaches a constant BEC asymptote in imbalanced case. Therefore, population 
Tuesday, March 5, 2019 12:51PM  1:03PM 
F24.00009: Harmonic potential effect on the ground state of the “ge” model Jereson Silva Valencia, Rodrigo Castellanos Caro, Roberto Franco Alkalineearth fermionic atoms confined in onedimensional optical lattices can be described by the socalled "ge" model [Nat. Phys. 6, 289 (10)], which at half filling shows four interesting insulating phases (CDW, Orbital density wave (ODW), Spin Haldane (SH) and SpinPeierls) [PRB 91, 075121(15)]. However, the confining potential has not been considered so far, for this reason we explore an extended "ge" model where a harmonic potential for both ^{1}S_{0} (g) and ^{3}P_{0} (e) atoms was considered. Using the densitymatrix renormalization group method, we found that diverse insulating phase coexist in the ground state and that the spin Haldane and the spin Peierls phases disappear with the confining potential, meaning that these phases will not be observed in the experiments. The evolution of the CDW and the ODW phases around the middle of the trap was studied for different parameters. This work is motivated by recent experimental results about ^{171}Yb atoms confined in optical lattices [Arxiv:1810.00536v1]. 
Tuesday, March 5, 2019 1:03PM  1:15PM 
F24.00010: Lightcone like spreading of correlations in the Bose Hubbard model at strong coupling Malcolm Kennett, Matthew R Fitzpatrick We study the spreading of correlations in space and time after a quantum quench in the Bose Hubbard model. We derive equations of motion for the singleparticle Green's function within the contourtime formalism, allowing us to study dynamics in the strong coupling regime. We discuss the numerical solutions of these equations and calculate the singleparticle density matrix for quenches in the Mott phase. We demonstrate lightcone like spreading of correlations in the Mott phase in one, two, and three dimensions and calculate propagation velocities in each dimension. Our results show excellent agreement with existing results in one dimension and demonstrate the anisotropic spreading of correlations in higher dimensions. 
Tuesday, March 5, 2019 1:15PM  1:27PM 
F24.00011: Rigorous Results for the Ground States of the Spin2 BoseHubbard Model Hong Yang, Hosho Katsura In this work, we prove rigorous theorems for the ground states of the spin2 BoseHubbard model, concerning the magnetic properties, degeneracies and forms of the wave functions. The theorems are highly universal in the sense that they do not depend on the lattice structure (including spatial dimension), particle number and spinindependent interaction. 
Tuesday, March 5, 2019 1:27PM  1:39PM 
F24.00012: MetalInsulatorSuperconductor Transition in TwoChannel Interacting ManyBody Systems Theja De Silva Using a slaverotor approach within a meanfield theory, we study twochannel interacting systems to investigate the competition of metallic, Mottinsulating, and superconducting phases. Considering spin3/2 cold atoms on optical lattices as a model system and treating a spin3/2 atom as a bound state of a charge and a spin, we uncover a novel form of matter due to the competition between metal and superconducting phase. This novel unconventional phase emerges as a result of the global U(1) broken symmetries with respect to both roton and spinon fields. Further, we argue that the emergence of this unconventional phase is a generic phenomenon associates with many body systems where there are competing interactions. As such, we show that this unconventional phase can exist in rubidium doped fullerides under pressure. 
Tuesday, March 5, 2019 1:39PM  1:51PM 
F24.00013: Quantum Joule expansions in onedimensional lattices ShanWen Tsai, Jin Zhang, Yannick Meurice We discuss the expansion dynamics of nonintegrable systems that contain bosons or fermions in onedimensional lattices. The particles are initially confined in half of the system with a thermal state described by the canonical ensemble. At short times after we remove the barrier before the front hits the other boundary of the lattice, the radial velocity of the expansion is a constant. The center of mass is accelerated with a constant acceleration. At long times, local observables can be approximated by a thermal expectation of another canonical ensemble with an effective temperature. The weights for the diagonal ensemble and the canonical ensemble match well for high initial temperatures that correspond to negative effective final temperature after the expansion. The negative effective temperature for finite systems goes to positive inverse temperatures in the thermodynamic limit for bosons but is a true thermodynamic effect for fermions. We also compare the thermal entanglement entropy and density distribution in momentum space for the canonical ensemble, diagonal ensemble and instantaneous longtime states calculated by exact diagonalization. 
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