Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L27: Topological States in AMO Systems IIFocus Live
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Sponsoring Units: DAMOP DCMP Chair: Daniel Leykam, Center for Quantum Technologies, Singapore |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L27.00001: Realizing artificial topological matter in arrays of Rybderg atoms Invited Speaker: Thierry Lahaye In this talk I will show how Rydberg array platforms for quantum simulation allow for an original way of exploring topological phases of matter, by using the resonant dipole-dipole interaction between several Rydberg levels. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L27.00002: Symmetry-protected Topological Phases in Spinful Bosons with a Flat Band Hong Yang, Hayate Nakano, Hosho Katsura We theoretically demonstrate that interacting symmetry-protected topological (SPT) phases can be realized with ultracold spinful bosonic atoms loaded on lattices which has a flat band at the bottom of the band structure. Ground states of such systems are not conventional Mott insulators. We find that the many-body ground states can be exactly written down when certain parameters in the Hamiltonians are properly chosen. The spin and charge fluctuations at zero temperature together determine the SPT phases of the system, and the exact ground state turns out to serve as a representative state of the SPT phases. We study some concrete examples. In particular, we demonstrate that spin-1 bosons on a sawtooth chain can be in an SPT phase protected by Z2×Z2 spin rotation symmetry or time-reversal symmetry, and this SPT phase is a result of the spin fluctuation. We also show that spin-3 bosons on a kagome lattice can be in an SPT phase protected by D2 point group symmetry, this SPT phase is however a result of the charge fluctuation. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L27.00003: Spatial and Spectral Mode-Selection Effects in Topological Lasers with Frequency-Dependent Gain Matteo Seclì, Massimo Capone, Iacopo Carusotto Topological lasers are a new promising class of devices that exploit the protected edge modes of topological insulators for coherent light emission with unprecedented properties1,2. A common scheme to select the edge mode is to use a pump spatially localized on the border1; however, by going beyond the standard theory of broadband gain3,4 we have recently shown5 that a narrowband gain allows to promote lasing of a topologically protected edge mode even with a spatially uniform pumping, provided that the gain is centered in the topological bandgap. In this work we lift these requirements; by building a phase diagram of our topological laser, we show indeed that lasing into a topologically protected edge mode can be promoted even in the case of a spectrally wide gain centered at a bulk band frequency. Our scheme exploits the presence of an active, topologically trivial region surrounding the topologically non-trivial one; such a mechanism may provide an explanation to pioneering experimental observations2 that still await theoretical interpretation. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L27.00004: Topological Euler Class as a Dynamical Observable in Optical Lattices Nur Unal, Adrien Bouhon, Robert-Jan Slager The last years have witnessed rapid progress in the topological characterization of out-of-equilibrium systems. We report on robust signatures of a new type of topology—the Euler class—in such a dynamical setting [1]. The enigmatic invariant (ξ) falls outside conventional symmetry-eigenvalue indicated phases and, in simplest incarnation, is described by triples of bands that comprise a gapless pair featuring 2ξ stable band nodes, and a gapped band. These nodes host non-Abelian charges and can be further undone by converting their charge upon intricate braiding mechanisms, revealing that Euler class is a fragile topology. We demonstrate that quenching with nontrivial Euler Hamiltonian results in stable monopole-antimonopole pairs, which in turn induce a linking of momentum-time trajectories under the first Hopf map, making the invariant experimentally observable. Our results provide a basis for exploring new topologies and their interplay with crystalline symmetries in optical lattices beyond paradigmatic Chern insulators. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L27.00005: Restoring number conservation in quadratic bosonic Hamiltonians with dualities: Applications for quantum simulation and topological classification. Vincent Flynn, Emilio Cobanera, Lorenza Viola The breaking of number conservation in quadratic bosonic Hamiltonians can induce unwanted dynamical instabilities. By exploiting the pseudo-Hermitian structure built into these Hamiltonians, we show that as long as dynamical stability holds, one may always construct a non-trivial dual (unitarily equivalent) quadratic bosonic Hamiltonian, where only number-conserving hopping terms are present. In particular, we exemplify this construction for a bosonic analogue to Kitaev’s Majorana chain. Our duality may be used to identify local number-conserving models that approximate stable bosonic Hamiltonians without the need for parametric amplification and to implement non-Hermitian PT-symmetric dynamics in non-dissipative number-conserving bosonic systems. We describe how our approach may be useful for achieving analog quantum simulation of PT-symmetric Hamiltonians with significantly less experimental demand and increased robustness. We further discuss the implications of our duality transformation for computing topological invariants and classifying free bosonic Hamiltonians. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L27.00006: Quantum optics meets topology: individual and collective phenomena Alejandro Gonzalez-Tudela Recent experimental advances allow one to engineer topological models in bosonic systems like photonic crystals, coupled microwave resonators, or optical lattices experiments, among other platforms [1]. In parallel, experimental progress is also being made to couple quantum emitters to such platforms in order to obtain (or simulate) light-matter Hamiltonians [2-4] with topological photons. The emergent behaviour and applications of the marriage between toplogy and quantum optics remain, except few exceptions [5], mostly unexplored. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L27.00007: Persistent homology of topological band structures Daniel Leykam, Dimitris Angelakis Persistent homology is a powerful machine learning technique for classifying complex systems or data sets, based on computing topological features over a range of spatial or energy scales. There is growing interest in applying persistent homology to characterize complex condensed matter systems, with recent applications including the classification of multiqubit entangled states and identification of hidden order in interacting spin models. In this work, we propose to use persistent homology to characterize band structures of periodic lattices. Using the Haldane model as an example, we show that persistent homology is able to reliably identify novel band structures including degenerate ``moat'' band minima and transitions between trivial and non-trivial Chern insulating phases. Our method is promising for the characterization of more complex wave systems with many internal degrees of freedom, such as Moire superlattices and superconducting circuits. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L27.00008: Driven-dissipative creation of a topologically ordered state (AKLT state) Vaibhav Sharma, Erich Mueller Dissipation of a quantum system coupled to an environment often destroys a quantum state of interest, but if carefully engineered, it can be used as a tool to prepare interesting quantum states. We propose an experimentally viable method to dissipatively create the AKLT (Affleck-Lieb-Kennedy-Tasaki) state which exhibits symmetry protected topological order. We analyze a system of lattice bosons, which are constrained to move in a one dimensional tilted optical lattice and couple them to a bosonic superfluid bath. We use a coherent raman beam to drive rabi oscillations of atoms between the lowest two motional bands of nearest neighbor sites. Under the driven-disipative process, the AKLT state emerges as the only steady state. We use exact diagonalization and DMRG methods to calculate the time scale for state preparation and find that the state preparation time scales qudratically with the system size. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L27.00009: Realizing Z2 phases and Majorana Spectroscopy in nearest-neighbor paired Bose-Hubbard systems Smitha Vishveshwara, David Minot Weld The connection between transverse XY spin chains and the fermionic Kitaev chain with nearest-neighbor hopping and pairing has been well known for decades, and has lately drawn attention for its rich phase diagram and relevance to realizations of Majorana fermions. Here, we study the novel system comprised of a Bose-Hubbard chain connected to a reservoir that can generate analogous pairing terms for bosons. We describe a cold-atom realization of such a system in a biased zig-zag optical lattice. We show that in certain limits, the Bosonic Kitaev chain maps on to the XY spin chain, resulting in an unsual Z2 phase that has number fluctuation but no off-diagonal long range order associated with boson condensation. Noteworthy features include the possibility of a strongly correlated many-body qubit ground state and the potential for cold-atom measurements of the Kitaev chain energy spectrum, including degenerate zero-energy states corresponding to Majorana fermionic bound states. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L27.00010: The effect of atom motion in Rydberg-atom quantum spin models Zewen Zhang, Bhuvanesh Sundar, Ming Yuan, Kaden Hazzard Ultracold Rydberg atoms in optical lattices and tweezers can realize quantum spin models. Recent experiments on one such system [1] have revealed dynamics not fully explained by coherent numerical calculations, pointing towards atom motion as a source of these deviations. In this talk, we show that atom motion indeed can semi-quantitatively explain the experimentally observed behavior. We study the effect of motion during quenches and ramps of 2D Rydberg atom systems nominally described by Ising models. As the motional degrees of freedom make it hard to solve the system with exact diagonalization or similar techniques, we employ the discrete truncated Wigner approximation (dTWA). Our results reveal that motional effects accumulate on timescales comparable to the interaction timescale in Ref. [1], suppressing correlation growth. Our results semi-quantitatively agree, without fitting, with Ref. [1]’s phenomenologically-proposed and experimentally-fit two-body interaction noise model. We discuss how this atomic motion will depend on atom species, lattice depth, Rydberg principal quantum number, and other important experimental variables. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L27.00011: Squaring the fermion: The threefold way and the fate of zero modes Qiao-Ru Xu, Vincent Flynn, Abhijeet Alase, Emilio Cobanera, Lorenza Viola, Gerardo Ortiz In the spirit of Dirac's derivation of a fermionic theory by "taking the square root" of the bosonic Klein-Gordon equation, we present a squaring procedure, mapping fermionic to bosonic theories, that helps establish a threefold way topological classification of stable noninteracting bosonic matter. The ephemeral nature of boundary states and the topological triviality of noninteracting, zero-temperature bosonic phases are supported by three no-go theorems, although excitations of those same phases may display topologically nontrivial characteristics. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L27.00012: Observability of a Majorana phase transition in a few-body model Jared Bland, Chris H Greene, Birgit Wehefritz-Kaufmann There is a strong interest in number conserving systems that exhibit Majorana fermions as quasiparticles. We utilize a number conserving analog of the Kitaev wire model due to Iemini et al. in the small-lattice limit to examine topological properties in a realistic ultracold atomic model. This interacting model exhibits several signatures of a topological regime, and the mutual information of opposite ends of the lattice displays a sharp transition even in the few-body limit. Previous results are extended by giving additional experimental signatures to distinguish the topological from the non-topological regime and by calculating timescales to study the transition and experimentally observe Majorana quasiparticles in this system (see the preprint arXiv:2006.08062). |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L27.00013: Stabilizing topological superfluidity of cold fermions in two-dimensional optical lattices Junhua Zhang, Sumanta Tewari, Vito W Scarola Theoretical studies have shown that identical fermions in a two-dimensional lattice can form a topological superfluid state, most notably a chiral p-wave pairing state, in the presence of attractive interactions. But the critical temperature is rather low as the system develops an instability towards phase separation with increasing interactions. This makes it experimentally challenging to realize a topological superfluid phase. We study the stability of the chiral p-wave phase against phase separation for spinless fermions in different lattices and find that the competition is common in the presence of nearest-neighbor attractions. Therefore, preventing phase separation is important to acquire higher critical temperatures for lattice fermions. To this end, we consider adding a longer-range repulsion to the short-range attraction in the system and find a strong suppression of the phase separation instability in favor of the chiral p-wave superfluid phase. We also discuss how to engineer the desired interactions in experiments with dipolar fermions. |
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