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...

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 demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron 173 Yb atoms. By mapping the electronic states onto effective sites along a synthetic "electronic" dimension, we have engineered fermionic ladders with synthetic magnetic flux in an experimental configuration that has allowed us to achieve uniform fluxes on a lattice with minimal requirements and unprecedented tunability. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases. DOI: 10.1103/PhysRevLett.117.220401 Ultracold atoms are emerging as a very versatile platform for the investigation of topological states of matter [1], thanks to the possibility of using laser light to synthesize artificial gauge fields [2,3] and to engineer lattices with topological band structures [4][5][6][7][8]. A prime element for the emergence of nontrivial topological properties is the presence of spin-orbit coupling (SOC) [9,10], locking the spin of the particles to their motion. This interaction was first synthesized in cold atomic gases by using twophoton Raman transitions [11] coupling two hyperfine spin states with a transfer of momentum. The coupling between spin states also enables a new powerful tool for engineering topological states of matter, which relies on the "synthetic dimension" (SD) concept [12,13]. According to this approach, the internal states of an atom are treated as effective sites along a synthetic lattice dimension, and coherent coupling between them is interpreted in terms of an effective tunneling. This idea has recently been realized in Refs. [14,15], where synthetic flux ladders have been implemented by using the spin degree of freedom, and has allowed the first observation of chiral edge states in ultracold atomic systems. Its extension has inspired several proposals, opening the way, e.g., to the observation of new quantum states [16,17], to the detection of fractional charge pumping [18,19], or to the observation of the four-dimensional quantum Hall effect [20].In this Letter, we demonstrate that SOC and SDs can be efficiently implemented by exploiting different degrees of freedom, specifically, the long-lived electronic state of alkaline-earth(-like) atoms. By using the technology developed in the context of optical atomic clocks, we induce a coherent coupling between the ground state g ¼ 1 S 0 and the metastable state e ¼ 3 P 0 (lifetime ∼20 s) of ultracold 173 Yb atoms. Since the two states are separated by an optical energy, it is possible to have a sizable transfer of momentum with a single-photon transition, as pointed out An ultranarrow clock laser with wavelength λ C drives the singlephoton transition between the ground state g ¼ 1 S 0 and the long...

We report on the experimental observation of a strongly interacting gas of ultracold two-electron fermions with an orbital degree of freedom and magnetically tunable interactions. This realization has been enabled by the demonstration of a novel kind of Feshbach resonance occurring in the scattering of two 173 Yb atoms in different nuclear and electronic states. The strongly interacting regime at resonance is evidenced by the observation of anisotropic hydrodynamic expansion of the two-orbital Fermi gas. These results pave the way towards the realization of new quantum states of matter with strongly correlated fermions with an orbital degree of freedom. DOI: 10.1103/PhysRevLett.115.265301 PACS numbers: 67.85.Lm, 34.50.Cx Recent theoretical and experimental work has evidenced how quantum gases of two-electron atoms represent extraordinary systems for the development of a new generation of quantum simulators of fermionic matter. They provide realizations of multicomponent fermionic gases with a tunable number of nuclear spin states and SUðNÞ-symmetric interactions [1][2][3]. In addition, they offer the unique feature of an additional electronic (orbital) degree of freedom, over which coherent quantum control can be achieved by means of the technology developed in the context of optical atomic clocks [4]. Recently, a strong spin-exchange interaction between 173 Yb fermions in different orbital states has been observed, paving the way for the realization of orbital quantum magnetism and of the Kondo lattice model [5,6].Despite these exciting perspectives, up to now twoelectron atoms have lacked the tunability of interactions that is provided by Feshbach resonances in the case of alkalis. Indeed, magnetic Feshbach resonances in ultracold gases of alkali atoms [7] have allowed breakthrough achievements, including unprecedented studies of strongly interacting fermions, with the demonstration of highdensity molecular gases and the exploration of fermionic superfluidity at the Bose-Einstein condensate (BEC)-BCS crossover [8]. A similar tunability for two-electron atoms would open totally new avenues, including the study of the crossover in a novel system with an orbital degree of freedom and the investigation of topological fermionic superfluids [9]. However, the zero electronic angular momentum in the ground state of two-electron atoms precludes the existence of accessible and useful magnetic Feshbach resonances. While optical Feshbach resonances in two-electron atoms have been proposed [10] and observed experimentally [11,12], their actual implementation still suffers from severe intrinsic difficulties, such as heating and losses, preventing the observation of true many-body quantum physics, although novel promising schemes have been very recently investigated [13].In this Letter we report on the first realization of a strongly interacting gas of two-electron fermionic atoms with an orbital degree of freedom and tunable interactions. We take advantage of a recently proposed orbital Feshbach resonance [9] affecting ...