Ultracold Lattice Gases with Periodically Modulated Interactions

Abstract

We show that a time-dependent magnetic field inducing a periodically modulated scattering length may lead to interesting novel scenarios for cold gases in optical lattices, characterized by a nonlinear hopping depending on the number difference at neighboring sites. We discuss the rich physics introduced by this hopping, including pair superfluidity, exactly defect-free Mott-insulator states for finite hopping, and pure holon and doublon superfluids. We also address experimental detection, showing that the introduced nonlinear hopping may lead in harmonically trapped gases to abrupt drops in the density profile marking the interface between different superfluid regions.PACS numbers: 37.10. Jk, 67.85.Hj, 73.43.Nq Ultracold atoms in optical lattices formed by laser beams provide an excellent environment for studying lattice models of general relevance in condensed-matter physics, and in particular, variations of the celebrated Hubbard model [1,2]. Cold lattice gases allow for an unprecedented degree of control of various experimental parameters, even in real time. In particular, interparticle interactions can be changed by means of Feshbach resonances [3]. Moreover, recent milestone achievements allow for site-resolved detection, permitting the study of in situ densities [4,5], and more involved measurements, as that of nonlocal parity order [6].The modulation of the lattice parameters in real time opens interesting possibilities of control and quantum engineering. In particular, a periodic lattice shaking translates by means of Floquet's theorem [7,8] into a modified hopping constant [9], which may even reverse its sign as shown in experiments [10,11]. This technique has been employed to drive the Mott-insulator (MI) to superfluid (SF) transition [12], and to simulate frustrated classical magnetism [13]. Recent experiments have explored as well the fascinating perspectives offered by periodically driven lattices in strongly correlated gases [14,15].The effective Hubbard-like models describing ultracold lattice gases are typically characterized by a hopping independent of the number of particles at the sites. This is, however, not necessarily the case. Multiband physics [16][17][18] and dipolar interactions for sufficiently large dipole moments [19] may lead to occupation-dependent hopping. A major consequence of nonlinear hopping is the possibility to observe pair superfluidity (PSF) [19,20], which resembles pairing in SF Fermi gases, although for bosons superfluidity exists as well without pairing.In this Letter, we consider a cold lattice gas in the presence of a periodically modulated magnetic field. In the vicinity of a Feshbach resonance, this field induces modulated interparticle interactions [21]. Interestingly, Ref.[22] has shown that periodic modulations of the interaction strength may lead to a many-body coherent destruction of tunneling in two-mode Bose-Einstein condensates. As shown below, the generalization of this effect to lattice gases leads under proper conditions to an effective Hubbard-like ...

Compacton matter waves in binary Bose gases under strong nonlinear management

“…Besides compacton excitations, periodic modulations of the scattering lengths can be used to create density dependent gauge fields [4], this being presently a field of rapidly growing interest, connected with interesting physical phenomena, including pair superfluidity, exactly-defect free Mott-insulator states etc. [5]. Properties of the superfluid -Mott transition in a 2D square and a 3D cubic optical lattice with periodic modulation of the atomic scattering length have been investigated in [6].…”

Density-Dependent Synthetic Gauge Fields Using Periodically Modulated Interactions

“…As shown in Refs. [41,42], a sufficiently fast modulation of the interactions leads to an effective model with a density-dependent hopping (as discussed in the Supplemental Material [46], just modulating the interactions PRL 113, 215303 (2014) P H Y S I C A L …”

“…In particular, periodic lattice shaking results in a modified hopping rate [34][35][36], which has been employed to drive the superfluid (SF) to Mott insulator (MI) transition [37], to simulate frustrated classical magnetism [38], and to create tunable gauge potentials [16]. Interestingly, a periodically modulated magnetic field may be employed in the vicinity of a Feshbach resonance to induce periodically modulated interactions, which result in a nonlinear hopping rate that depends on the occupation differences at neighboring sites [41][42][43].In this Letter, we show that combining periodic interactions and Raman-assisted hopping may induce a densitydependent gauge field in 1D lattices. The created field results in a density-dependent shift of the momentum distribution that may be probed in time-of-flight (TOF) experiments.…”

Binary matter-wave compactons induced by inter-species scattering length modulations

“…Experimentally, this phenomenon has been recently observed in BEC in deep OL with periodic time modulatations of the interactions [10]. We also remark that the SNM of the scattering lengths is presently used to investigate several interesting physical phenomena related to new quantum phases [11,12], artificial gauge fields and spin-orbit couplings [13,14], in BEC systems.…”