Light-induced spin-orbit coupling is a flexible tool to study quantum magnetism with ultracold atoms. In this work we show that spin-orbit coupled Bose gases in a one-dimensional optical lattice can be mapped into a two-leg triangular ladder with staggered flux following a lowest-band truncation of the Hamiltonian. The effective flux and the ratio of the tunneling strengths can be independently adjusted to a wide range of values. We identify a certain regime of parameters where a hard-core boson approximation holds and the system realizes a frustrated triangular spin ladder with tunable flux. We study the properties of the effective spin Hamiltonian using the density-matrix renormalization-group method and determine the phase diagram at half-filling. It displays two phases: a uniform superfluid and a bond-ordered insulator. The latter can be stabilized only for low Raman detuning. Finally, we provide experimentally feasible trajectories across the parameter space of the SOC system that cross the predicted phase transition.

%B The European Physical Journal D %V 74 %U https://link.springer.com/article/10.1140/epjd/e2020-10129-1 %& 123 %R 10.1140/epjd/e2020-10129-1 %0 Journal Article %J Phys. Rev. A %D 2019 %T Coherent spin mixing via spin-orbit coupling in Bose gases %A J. Cabedo %A J. Claramunt %A A. Celi %A Y. Zhang %A V. Ahufinger %A J. Mompart %XWe study beyond-mean-field properties of interacting spin-1 Bose gases with synthetic Rashba-Dresselhaus spin-orbit coupling at low energies. We derive a many-body Hamiltonian following a tight-binding approximation in quasimomentum space, where the effective spin dependence of the collisions that emerge from spin-orbit coupling leads to dominant correlated tunneling processes that couple the different bound states. We discuss the properties of the spectrum of the derived Hamiltonian and its experimental signatures. In a certain region of the parameter space, the system becomes integrable, and its dynamics becomes analogous to that of a spin-1 condensate with spin-dependent collisions. Remarkably, we find that such dynamics can be observed in existing experimental setups through quench experiments that are robust against magnetic fluctuations.

%B Phys. Rev. A %V 100 %P 063633 %8 Dec %U https://link.aps.org/doi/10.1103/PhysRevA.100.063633 %R 10.1103/PhysRevA.100.063633 %0 Journal Article %J Frontiers in Physics %D 2019 %T Diffusion Through a Network of Compartments Separated by Partially-Transmitting Boundaries %A G. Muñoz-Gil %A M. A. Garcia-March %A C. Manzo %A A. Celi %A M. Lewenstein %XWe study the random walk of a particle in a compartmentalized environment, as realized in biological samples or solid state compounds. Each compartment is characterized by its length L and the boundaries transmittance T. We identify two relevant spatio-temporal scales that provide alternative descriptions of the dynamics: (i) the microscale, in which the particle position is monitored at constant time intervals; and (ii) the mesoscale, in which it is monitored only when the particle crosses a boundary between compartments. Both descriptions provide—by construction—the same long time behavior. The analytical description obtained at the proposed mesoscale allows for a complete characterization of the complex movement at the microscale, thus representing a fruitful approach for this kind of systems. We show that the presence of disorder in the transmittance is a necessary condition to induce anomalous diffusion, whereas the spatial heterogeneity reduces the degree of subdiffusion and, in some cases, can even compensate for the disorder induced by the stochastic transmittance.

%B Frontiers in Physics %V 7 %P 31 %U https://www.frontiersin.org/article/10.3389/fphy.2019.00031 %R 10.3389/fphy.2019.00031 %0 Journal Article %J Nature Photonics %D 2019 %T Knotting fractional-order knots with the polarization state of light %A E. Pisanty %A G. J. Machado %A V. Vicuña-Hernández %A A. Picón %A A. Celi %A J. P. Torres %A M. Lewenstein %XThe fundamental polarization singularities of monochromatic light are normally associated with invariance under coordinated rotations: symmetry operations that rotate the spatial dependence of an electromagnetic field by an angle *θ* and its polarization by a multiple *γθ* of that angle. These symmetries are generated by mixed angular momenta of the form *J*_{γ} = *L* + *γS*, and they generally induce Möbius-strip topologies, with the coordination parameter *γ* restricted to integer and half-integer values. In this work we construct beams of light that are invariant under coordinated rotations for arbitrary rational *γ*, by exploiting the higher internal symmetry of ‘bicircular’ superpositions of counter-rotating circularly polarized beams at different frequencies. We show that these beams have the topology of a torus knot, which reflects the subgroup generated by the torus-knot angular momentum *J*_{γ}, and we characterize the resulting optical polarization singularity using third- and higher-order field moment tensors, which we experimentally observe using nonlinear polarization tomography.

The year 2015 was the International Year of Light. However, it also marked, the 20th anniversary of the first observation of Bose–Einstein condensation in atomic vapors by Eric Cornell, Carl Wieman and Wolfgang Ketterle. This discovery could be considered as one of the greatest achievements of quantum optics that has triggered an avalanche of further seminal discoveries and achievements. For this reason we devote this essay for the focus issue on ‘Quantum Optics in the International Year of Light’ to the recent revolutionary developments in quantum optics at the frontiers of all physics: atomic physics, molecular physics, condensed matter physics, high energy physics and quantum information science. We follow here the lines of the introduction to our book ‘Ultracold atoms in optical lattices: Simulating quantum many-body systems’ (Lewenstein et al 2012 Ultracold Atoms in Optical Lattices: Simulating Quantum Many-body Systems (Oxford: University Press)), and to a lesser extent the review article M Lewenstein et al (2007 Adv. Phys. 56 [http://https://dx.doi.org/10.1080/00018730701223200] 243 ). The book, however, was published in 2012, and many things has happened since then—the present essay is therefore upgraded to include the latest developments.

%B Physica Scripta %V 92 %P 013003 %U http://stacks.iop.org/1402-4896/92/i=1/a=013003