Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, we detect the existence of the edge states, investigate the onset of chirality as a function of the bulk-edge coupling, and observe the edge-cyclotron orbits induced during a quench dynamics. The realization of fermionic chiral edge states is a fundamental achievement, which opens the door towards experiments including edge state interferometry and the study of non-Abelian anyons in atomic systems.Ultracold atoms in optical lattices represent an ideal platform to investigate the physics of condensed-matter problems in a fully tunable, controllable environment [1,2]. One of the remarkable achievements in recent years has been the realization of synthetic background gauge fields, akin to magnetic fields in electronic systems. Indeed, by exploiting light-matter interaction, it is possible to imprint a Peierls phase onto the atomic wavefunction, which is analogous to the Aharanov-Bohm phase experienced by a charged particle in a magnetic field [3][4][5]. These gauge fields, first synthesized in Bose-Einstein condensates [6], have recently allowed for the realization of the HarperHofstadter Hamiltonian in ultracold bosonic 2D lattice gases [7,8], paving the way towards the investigation of different forms of bulk topological matter in bosonic atomic systems [5,9]. In the present work we are instead interested in the edge properties of fermionic systems under the effects of a synthetic gauge field. Fermionic edge states are a fundamental feature of 2D topological states of matter, such as quantum Hall and chiral spin liquids [10,11]. Moreover, they are robust against changing the geometry of the system by keeping its topology, and can be observed even on Hall ribbons [12]. In addition, they offer very attractive perspectives in quantum science, such as the realization of robust quantum information buses [13], and they are ideal starting points for the realization of non-Abelian anyons akin to Majorana fermions [14,15].Here, we report the observation of chiral edge states in a system of neutral fermions subjected to a synthetic magnetic field. We exploit the high level of control in our system to investigate the emergence of chirality as a function of the Hamiltonian couplings. These results have been enabled by an innovative experimental approach, where an internal (nuclear spin) degree of freedom of the atoms is used to encode a lattice structure lying in an "extra dimension" [12], providing direct access to edge physics. In addition, we validate the chiral nature of our FIG. 1. A synthetic gauge field in a synthetic dimension. a. We confine the mot...
Using a species-selective dipole potential, we create initially localized impurities and investigate their interactions with a majority species of bosonic atoms in a one-dimensional configuration during expansion. We find an interaction-dependent amplitude reduction of the oscillation of the impurities' size with no measurable frequency shift, and study it as a function of the interaction strength. We discuss possible theoretical interpretations of the data. We compare, in particular, with a polaronic mass shift model derived following Feynman variational approach.
Correlations in systems with spin degree of freedom are at the heart of fundamental phenomena, ranging from magnetism to superconductivity. The e ects of correlations depend strongly on dimensionality, a striking example being one-dimensional (1D) electronic systems, extensively studied theoretically over the past fifty years 1-7 . However, the experimental investigation of the role of spin multiplicity in 1D fermions-and especially for more than two spin components-is still lacking. Here we report on the realization of 1D, strongly correlated liquids of ultracold fermions interacting repulsively within SU(N) symmetry, with a tunable number N of spin components. We observe that static and dynamic properties of the system deviate from those of ideal fermions and, for N > 2, from those of a spin-1/2 Luttinger liquid. In the large-N limit, the system exhibits properties of a bosonic spinless liquid. Our results provide a testing ground for many-body theories and may lead to the observation of fundamental 1D e ects 8 . One-dimensional quantum systems show specific, sometimes counterintuitive behaviours that are absent in the 3D world. These behaviours, predicted by many-body models of interacting bosons 9 and fermions 2-4 , include the 'fermionization' of bosons 10 and the separation of spin and density (most commonly referred to as 'charge') branches in the excitation spectrum of interacting fermions. The last phenomenon is predicted within the celebrated Luttinger liquid model 5 , which describes the low-energy excitations of interacting spin-1/2 fermions. Although the Luttinger approach describes qualitatively the physics of a number of 1D systems 11,12 , the problem of how to extend it to a more detailed description of real systems has puzzled physicists over the years 7 . In this exploration the physics of spin has played a key role.Ultracold atoms have proved to be a precious resource to study 1D physics, as they afford exceptional control over experimental parameters. Most of the experiments so far have been performed with spinless bosons, which for instance led to the realization of a Tonks-Girardeau gas 13,14 . On the other hand, 1D ultracold fermions are a promising system to observe a number of elusive phenomena, such as Stoner's itinerant ferromagnetism 15 and the physics of spin-incoherent Luttinger liquids 6 . However, only a few pioneering works, dealing with spin-1/2 particles [16][17][18] , have been reported so far.In parallel, ultracold two-electron atoms have been recently proposed for the realization of large-spin systems with SU(N ) interaction symmetry 19,20 , and the first experimental investigations have been reported 21 . This novel platform enables the simulation of 1D systems with a high degree of complexity, including spin-orbitcoupled materials 22 or SU(N ) Heisenberg and Hubbard chains 23,24 . Moreover, the investigation of these multi-component fermions is relevant for the simulation of field theories with extended SU(N ) symmetries 25 . In this Letter we report on the realization of ...
We produce Bose-Einstein condensates of two different species, 87 Rb and 41 K, in an optical dipole trap in proximity of interspecies Feshbach resonances. We discover and characterize two Feshbach resonances, located around 35 and 79 G, by observing the three-body losses and the elastic crosssection. The narrower resonance is exploited to create a double species condensate with tunable interactions. Our system opens the way to the exploration of double species Mott insulators and, more in general, of the quantum phase diagram of the two species Bose-Hubbard model. Ultracold atomic gases seem uniquely suited to experimentally realize and investigate physics long studied in the domain of condensed matter and solid state physics, with the distinct advantage that specific effects are better isolated from unnecessary complications often present in condensed samples. The paradigmatic superfluid to Mott insulator transition of a condensate in an optical lattice [1] confirmed the predictions of the Bose-Hubbard model [2,3], originally introduced to describe superfluid Helium. With two species, the zero-temperature diagram of quantum phases is much richer than the simple duplication of the single species ' [4]. Indeed it has been proposed that two species obeying an extended BoseHubbard model can mimick the physics of lattice spins described by the Heinsenberg model [5,6] and give rise to yet unobserved quantum phases, like the double Mott insulator and the supercounterflow regime [7], with peculiar transport properties. Therefore, a double species condensate in an optical lattice stands as a promising candidate system for quantum simulations. Recently, the investigation of the two-species BH was started from the regime where one species exhibits the loss of phase coherence usually associated with the Mott insulator transition, while the other is completely delocalized [8]. Already at this stage, the presence of two species leads to a surprising shift of the critical point, which is now object of intense theoretical work [9].In addition, a double Mott insulator is expectedly extremely useful to produce heteronuclear polar molecules [10], since the association efficiency strongly depends on the phase space overlap of the two species [11]. The rapid losses of associated molecules observed for bosonic systems could be largely suppressed by the presence of the three-dimensional optical lattice [12], if most of the sites are occupied with only one atom per species. Both these research avenues require the dynamic control of interspecies interactions, along with a well established collisional model.
The competition of dipole-dipole and contact interactions leads to exciting new physics in dipolar gases, well-illustrated by the recent observation of quantum droplets and rotons in dipolar condensates. We show that the combination of the roton instability and quantum stabilization leads under proper conditions to a novel regime that presents supersolid properties, due to the coexistence of stripe modulation and phase coherence. In a combined experimental and theoretical analysis, we determine the parameter regime for the formation of coherent stripes, whose lifetime of a few tens of milliseconds is limited by the eventual destruction of the stripe pattern due to three-body losses. Our results open intriguing prospects for the development of long-lived dipolar supersolids. arXiv:1811.02613v2 [cond-mat.quant-gas]
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