We present an implementation of a continuous matrix product state for two-component fermions in one-dimension. We propose a construction of variational matrices with an efficient parameterization that respects the translational symmetry of the problem (without being overly constraining) and readily meets the regularity conditions that arise from removing the ultraviolet divergences in the kinetic energy. We test the validity of our approach on an interacting spin-1/2 system and observe that the ansatz correctly predicts the ground state magnetic properties for the attractive spin-1/2 Fermi gas, including the phase-oscillating pair correlation function in the partially polarized regime.Comment: 6 pages, 5 figure

The recent experimental realization of spin-orbit (SO) coupling for spin-1 ultracold atoms opens an interesting avenue for exploring SO-coupling-related physics in large-spin systems, which is generally unattainable in electronic materials. In this paper, we study the effects of interactions between atoms on the ground states and collective excitations of SO-coupled spin-1 Bose-Einstein condensates (BECs) in the presence of a spin-tensor potential. We find that ferromagnetic interaction between atoms can induce a stripe phase exhibiting in-phase or out-of-phase modulating patterns between spin-tensor and zero-spin-component density waves. We characterize the phase transitions between different phases using the spin-tensor density as well as the collective dipole motion of the BEC. We show that there exists a double maxon-roton structure in the Bogoliubov-excitation spectrum, attributed to the three band minima of the SO-coupled spin-1 BEC.Comment: 8 pages, 4 figure

Static, dynamic, and topological properties of hollow systems differ from those that are fully filled as a result of the presence of a boundary associated with an inner surface. Hollow Bose-Einstein condensates (BECs) naturally occur in various ultracold atomic systems and possibly within neutron stars but have hitherto not been experimentally realized in isolation on Earth because of gravitational sag. Motivated by the expected first realization of fully closed BEC shells in the microgravity conditions of the Cold Atomic Laboratory aboard the International Space Station, we present a comprehensive study of spherically symmetric hollow BECs as well as the hollowing transition from a filled sphere BEC into a thin shell through central density depletion. We employ complementary analytic and numerical techniques in order to study equilibrium density profiles and the collective mode structures of condensate shells hosted by a range of trapping potentials. We identify concrete and robust signatures of the evolution from filled to hollow structures and the effects of the emergence of an inner boundary, inclusive of a dip in breathing-mode-type collective mode frequencies and a restructuring of surface mode structure across the transition. By extending our analysis to a two-dimensional transition of a disk to a ring, we show that the collective mode signatures are an essential feature of hollowing, independent of the specific geometry. Finally, we relate our work to past and ongoing experimental efforts and consider the influence of gravity on thin condensate shells. We identify the conditions under which gravitational sag is highly destructive and study the mode-mixing effects of microgravity on the collective modes of these shells.arXiv:1712.04428v2 [cond-mat.quant-gas]

The experimental realization of emergent spin-orbit coupling through laser-induced Raman transitions in ultracold atoms paves a way for exploring novel superfluid physics and simulating exotic many-body phenomena. A recent proposal with the use of Laguerre-Gaussian lasers enables another fundamental type of coupling between spin and orbital angular momentum (SOAM) in ultracold atoms. We hereby study quantum phases of a realistic Bose-Einstein condensate (BEC) with this synthetic SOAM coupling in a disk-shaped geometry, respecting radial inhomogeneity of the Raman coupling. We find that the experimental system naturally resides in a strongly interacting regime in which the phase diagram significantly deviates from the single-particle picture. The interplay between SOAM coupling and interaction leads to rich structures in spin-resolved position and momentum distributions, including a stripe phase and various types of immiscible states. Our results would provide a guide for an experimental investigation of SOAM-coupled BECs.

Spin-orbit coupling (SOC) plays a crucial role in many branches of physics. In this context, the recent experimental realization of the coupling between spin and linear momentum of ultracold atoms opens a completely new avenue for exploring new spin-related superfluid physics. Here we propose that another important and fundamental SOC, the coupling between spin and orbital angular momentum (SOAM), can be implemented for ultracold atoms using higher-order Laguerre-Gaussian laser beams to induce Raman coupling between two hyperfine spin states of atoms. We study the ground-state phase diagrams of SOAM-coupled Bose-Einstein condensates on a ring trap and explore their applications in gravitational force detection. Our results may provide the basis for further investigation of intriguing superfluid physics induced by SOAM coupling, such as collective excitations.

We study one-component fermions in chain lattices with proximity-induced superconducting gap and interparticle short-range interaction, capable of hosting Majorana fermions. By systematically tracking various physical quantities, we show that topological states and topological phase transitions in the system can be identified by multiple signatures in thermodynamic quantities and pair-condensate properties, in good agreement with the known signatures in the ground-state energy and entanglement spectrum. We find the disappearance of the topological phase in a largely attractive regime, in which the system undergoes a first-order transition between two topologically trivial states. In addition, the stability of the signatures against finite size, disorder, and inhomogeneity is analyzed. Our results provide additional degrees of freedom for the characterization of topological states with interaction and for the experimental detection of emergent Majorana fermions.

The recent experimental realization of spin-orbit coupling for ultracold atomic gases provides a powerful platform for exploring many interesting quantum phenomena. In these studies, spin represents spin vector (spin-1/2 or spin-1) and orbit represents linear momentum. Here we propose a scheme to realize a new type of spin-tensor-momentum coupling (STMC) in spin-1 ultracold atomic gases. We study the ground state properties of interacting Bose-Einstein condensates (BECs) with STMC and find interesting new types of stripe superfluid phases and multicritical points for phase transitions. Furthermore, STMC makes it possible to study quantum states with dynamical stripe orders that display density modulation with a long tunable period and high visibility, paving the way for direct experimental observation of a new dynamical supersolid-like state.. Our scheme for generating STMC can be generalized to other systems and may open the door for exploring novel quantum physics and device applications.Introduction.-The coupling between matter and gauge field plays a crucial role for many fundamental quantum phenomena and practical device applications in condensed matter [1][2][3] and atomic physics [4]. A prominent example is the spin-orbit coupling, the coupling between a particle's spin and orbit (e.g., momentum) degrees of freedom, which is responsible for important physics such as topological insulators and superconductors [2,3]. In this context, recent experimental realization of spin-orbit coupling in ultracold atomic gases [5][6][7][8][9][10][11][12][13] opens a completely new avenue for investigating quantum many-body physics under gauge field [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].So far in most works on spin-orbit coupling in solid state and cold atomic systems, the spin degrees of freedom are taken as rank-1 spin vectors F i (i = x, y, z), such as electron spin-1/2 or pseudospins formed by atomic hyperfine states that can be large (e.g., spin-1 or 3/2). Experimentally, spin-orbit coupling for spin-1 Bose-Einstein condensates (BECs) has been realized recently [29,30] and interesting magnetism physics has been observed [31][32][33][34][35]. Mathematically, it is well known that there exist not only spin vectors, but also spin tensors [e.g., irreducible rank-2 spin-quadrupole tensorin a large spin (≥ 1) system. Therefore two natural questions are: i ) Can the coupling between spin tensors of particles and their linear momenta be realized in experiments? ii ) What new physics may emerge from such spin-tensor-momentum coupling (STMC)?In this Letter, we address these two questions by proposing a simple experimental scheme for realizing STMC for spin-1 ultracold atomic gases. Our scheme is based on slight modification of previous experimental setup [29] and is experimentally feasible. The STMC changes the band structure dramatically, leading to interesting new physics in the presence of many-body interactions between atoms. Although both bosons and fermions can be studied, here we only consider spi...

PACS 03.75.Kk -Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow PACS 67.85.De -Dynamic properties of condensates; excitations, and superfluid flow Abstract -Bose-Einstein condensate shells, while occurring in ultracold systems of coexisting phases and potentially within neutron stars, have yet to be realized in isolation on Earth due to the experimental challenge of overcoming gravitational sag. Motivated by the expected realization of hollow condensates by the space-based Cold Atomic Laboratory in microgravity conditions, we study a spherical condensate undergoing a topological change from a filled sphere to a hollow shell. We argue that the collective modes of the system show marked and robust signatures of this hollowing transition accompanied by the appearance of a new boundary. In particular, we demonstrate that the frequency spectrum of the breathing modes shows a pronounced depression as it evolves from the filled sphere limit to the hollowing transition. Furthermore, when the center of the system becomes hollow surface modes show a global restructuring of their spectrum due to the availability of a new, inner, surface for supporting density distortions. We pinpoint universal features of this topological transition as well as analyse the spectral evolution of collective modes in the experimentally relevant case of a bubble-trap.Quantum matter, when subject to transitions of a topological nature, undergoes fundamental changes in its properties [1]. Such transitions involve singular deformations of the underlying space inhabited by the system, be it real or abstract. For instance, the ripping action required to convert a sphere into a torus. In topological materials, which have recently gained prominent attention, matter can transform from being a trivial insulator to one having gapless surface states. The topological nature of the transition can be pinpointed through the calculation or measurement of an abstract Berry phase type global invariant associated with non-trivial winding, for instance, in momentum space [2]. Cold atomic systems, given their spectacular trapping and tuning capabilities, not only enable measuring such topological invariants [3-5], they offer a much more direct, real space version of a topological transition through purely changing physical geometry. As a pioneering instance, the realization of toroidal BoseEinstein condensates (BECs) [6,7] corresponds to a topo-(a) kuei.sun@utdallas.edu (b) clannert@smith.edu (c) smivish@illinois.edu logical structure characterized by a homotopy group that is not equivalent to that of a disk. Here we explore salient features associated with the hollowing out of a spherically filled BEC and subsequent formation of a closed, hollow shell. The filled and hollow BECs are topologically inequivalent in that they correspond to different second homotopy groups. In other words, unlike for the filled spherically symmetric BEC, a spherical surface within the hollow BEC that surrounds its center cannot be continuousl...