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Physical Review A

Matter-wave revival of binary mixtures in optical lattices

Miroslav Urbánek, Pavel Soldán

Published Sep 9, 2014• 1 citation
Publisher

Abstract

Quantum-phase collapse and revival are studied in a binary mixture of bosonic atomic species loaded in a one-dimensional optical lattice. Oscillations in the quasimomentum distribution are usually observed after a sudden quench of the lattice parameters from the superfluid regime to the Mott-insulator regime. The influence of one species dynamics on the collapse and revival oscillations in the quasimomentum distribution of the second species is examined. The nontrivial dependencies on the interspecies and intraspecies interactions are illustrated distinguishing between the zero-tunneling and nonzero-tunneling cases.

DOI
10.1103/physreva.90.033610

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•Aug 1, 2012•1 citation
Quantum-phase collapse and revival are studied in a binary mixture of bosonic atomic species loaded in a one-dimensional optical lattice. Oscillations in the quasimomentum distribution are usually observed after a sudden quench of the lattice parameters from the superfluid regime to the Mott-insulator regime. The influence of one species dynamics on the collapse and revival oscillations in the quasimomentum distribution of the second species is examined. The nontrivial dependencies on the interspecies and intraspecies interactions are illustrated distinguishing between the zero-tunneling and nonzero-tunneling cases.
We predict the existence of novel collapse and revival oscillations that are a distinctive signature of the short-range off-diagonal coherence. Starting with an atomic Mott state in a one-dimensional optical lattice, suddenly raising the lattice depth freezes particle–hole pairs in place and induces phase oscillations. The peak of the quasi-momentum distribution, revealed through time-of-flight interference, oscillates between a maximum occupation at zero quasi-momentum (the Γ point) and the edge of the Brillouin zone. We show that the population enhancements at the edge of the Brillouin zone are due to short-range coherence due to particle–hole pairs, and we find similar effects for fermions and Bose–Fermi mixtures in a lattice. Our results open a new dynamic probe for strongly correlated many-body states with short-range phase coherence that is distinct from the matter–wave collapse and revivals previously observed in the long-range coherent superfluid regime.
We study the quantum dynamics of cold Bose atoms in a double well. It is shown that self-trapping as well as population oscillations are common phenomena associated with nonlinear interactions. For larger U/tU/tU/t, multiparticle tunneling is damped and the quantum dynamics is dominated by single-particle tunneling. The many-body system can be effectively described in a truncated Fock space. It exhibits coherence-decoherence oscillations in the temporal evolution. We predict an interesting phenomenon of dynamical revival and collapse of matter wave fields in optical lattices in regimes near the superfluid--Mott-insulator phase boundary.
We study the dynamics of spin-1 atoms in a periodic optical-lattice potential and an external magnetic field in a quantum quench scenario where we start from a superfluid ground state in a shallow lattice potential and suddenly raise the lattice depth. The time evolution of the nonequilibrium state shows collective collapse-and-revival oscillations of matter-wave coherence as well as oscillations in the spin populations. We show that the complex pattern of these two types of oscillations reveals details about the superfluid and magnetic properties of the initial many-body ground state. Furthermore, we show that the strengths of the spin-dependent and spin-independent atom-atom interactions can be deduced from the observations. The Hamiltonian that describes the physics of the final deep lattice not only contains two-body interactions but also effective multibody interactions, which arise due to virtual excitations to higher bands. We derive these effective spin-dependent three-body interaction parameters for spin-1 atoms and describe how spin mixing is affected. Spinor atoms are unique in the sense that multibody interactions are directly evident in the in situ number densities in addition to the momentum distributions. We treat both antiferromagnetic (e.g., 23{}^{23}23Na) and ferromagnetic (e.g., 87{}^{87}87Rb and 41{}^{41}41K) condensates.
We study the collapse and revival of interference patterns in the momentum distribution of atoms in optical lattices using a projection technique to properly account for the fixed total number of atoms in the system. We consider the common experimental situation in which weakly interacting bosons are loaded into a shallow lattice, which is suddenly made deep. The collapse and revival of peaks in the momentum distribution is then driven by interactions in a lattice with essentially no tunneling. The projection technique allows to us to treat inhomogeneous (trapped) systems exactly in the case that noninteracting bosons are loaded into the system initially, and we use time-dependent density-matrix renormalization group techniques to study the system in the case of finite tunneling in the lattice and finite initial interactions. For systems of more than a few sites and particles, we find good agreement with results calculated via a naive approach, in which the state at each lattice site is described by a coherent state in the particle occupation number. However, for systems on the order of ten lattice sites, we find experimentally measurable discrepancies to the results predicted by this standard approach.
We study the dynamics of interacting superfluid bosons in a one-dimensional vertical optical lattice after a sudden increase of the lattice potential depth. We show that this system can be exploited to investigate the effects of strong interactions on Bloch oscillations. We perform theoretical modeling of this system, identify experimental challenges, and explore a regime of Bloch oscillations characterized by interaction-induced matter-wave collapse and revivals which modify the Bloch oscillations dynamics. In addition, we study three dephasing mechanisms: finite value of tunneling, effective three-body interactions, and a background harmonic potential. We also find that the center-of-mass motion in the presence of finite tunneling goes through collapse and revivals, giving an example of quantum transport where interaction-induced revivals are important. We quantify the effects of residual harmonic trapping on the momentum distribution dynamics and show the occurrence of an interaction-modified temporal Talbot effect. Finally, we analyze the prospects and challenges of exploiting Bloch oscillations of cold atoms in the strongly interacting regime for precision measurement of the gravitational acceleration ggg.
Quantum degenerate atomic gases offer a unique platform for the exploration of a wide variety of interacting many-body systems in a pristine environment, based on a set of powerful tools for the coherent control of the atoms' internal and external degrees of freedom. Here, we present experimental studies of strongly interacting bosonic mixtures in one-dimensional (1D) systems, in which the mobilities of the two species are independently controlled with a state-selective optical lattice. In a first experiment, we freeze out the tunneling of one species from a binary mixture, and study the formation of ``quantum emulsion'' states, where immobile atoms serve as a static, random disorder for a more mobile species. We investigate the 1D superfluid-to-insulator transition in the presence of this disorder, and make comparisons to the effects of quasi-disorder from an incommensurate optical lattice. We observe enhanced localization in the more random potential, highlighting the important role of correlations in disordered systems. Through a combined measurement of transport, localization, and excitation spectra, we are able to obtain strong evidence for observation of a disordered, insulating quantum phase, the 1D Bose glass. In a second experiment, we introduce a new experimental technique for the characterization of ultracold gases held in optical lattices. In analogy to neutron diffraction from solids, we use atomic de Broglie waves to non-destructively probe the spatial structure of 1D Mott insulators through elastic Bragg diffraction, and to probe inelastic band-structure excitations of more weakly interacting 1D Bose gases. Furthermore, we use the diffraction of matter waves to detect the formation of forced-antiferromagnetic ordering in a crystalline atomic spin mixture. Lastly, we study the dynamical response of matter waves to a periodically pulsed, incommensurate optical lattice, a situation that realizes a system of two coupled kicked quantum rotors. We observe that the coupling induces a suppression of energy growth at quantum resonances, and a localization-to-delocalization transition in momentum space for off-resonant driving. Our observations confirm a long-standing theoretical prediction for the two-rotor system, and illustrate how classical behavior can emerge from the evolution of a simple quantum system. | 193 pages