Probing spin dynamics from the Mott insulating to the superfluid regime in a dipolar lattice gas

Abstract

We analyze the spin dynamics of an out-of-equilibrium large spin dipolar atomic Bose gas in an optical lattice. We observe a smooth crossover from a complex oscillatory behavior to an exponential behavior throughout the Mott-to-superfluid transition. While both of these regimes are well described by our theoretical models, we provide data in the intermediate regime where dipolar interactions, contact interactions, and superexchange mechanisms compete. In this strongly correlated regime, spin dynamics and transport are coupled, which challenges theoretical models for quantum magnetism. DOI: 10.1103/PhysRevA.93.021603 Dipolar atoms and molecules loaded in optical lattices are a promising platform to study quantum many-body physics [1,2], and, in particular, quantum magnetism [3][4][5][6][7][8]. In dipolar systems, direct spin-spin interactions are provided by the dipole-dipole interaction (DDI) without relying on a superexchange mechanism [9]. Although magnetization changing collisions associated with the anisotropic character of dipolar interactions may introduce interesting exotic quantum phases [10][11][12][13], these off-resonant processes are often negligible. Then, dipolar interactions reduce to the following Hamiltonian,where2 (μ 0 being the magnetic permeability of vacuum, g the Landé factor, and μ B the Bohr magneton), r is the distance between atoms, θ 1,2 the angle between the magnetic field and the interatomic axis, and S ±,z i are the spin operators acting on atom i. This Hamiltonian, known as the secular dipolar Hamiltonian in the context of nuclear magnetic resonance [14], bears strong similarities to the XXZ model of quantum magnetism [9].Experimental investigations of such spin Hamiltonians have recently started, with dipolar molecules [15], and magnetic [16] and Rydberg [17] atoms, which have raised great interest [8,[10][11][12][13]18]. While these studies have focused on a localized regime where the particles are pinned to a well-defined position, in this Rapid Communication we investigate the case where magnetic atoms are free to move in an optical lattice. Thus spin dynamics and transport are coupled due to an interplay between superexchange mechanisms and dipolar spin exchange. Our experiment provides data in this regime which challenges theoretical descriptions.We study the spin-exchange dynamics of magnetic chromium 52 Cr bosonic atoms loaded in a three-dimensional (3D) optical lattice, across the Mott-to-superfluid transition [19]. We observe, as a function of the lattice depth, a crossover between two distinct behaviors. In the Mott phase, the spin dynamics displays a complex oscillatory behavior, as already studied in Ref. [16]. Although the physics is inherently many body due to strong correlations and the long-range nature of the dipolar interactions, we provide a quantitative interpretation of the oscillations due to intersite DDIs, using a simple model based on perturbation theory. In the superfluid regime, the spin dynamics shows an exponential behavior. Our data are then in go...

A generalized phase space approach for solving quantum spin dynamics

“…In particular, models of coupled spin-particles with long-range interactions have become a topic of intensive research because of important experimental progress. While models with spin S=1/2 have been implemented with many different setups, e.g.using polar molecules [15,17], Rydberg atoms [16,[18][19][20][21][22][23], trapped ions [24][25][26] and cavity QED systems [27,28], recently also models with larger spins S>1/2 have become a research focus in particular for experiments with magnetic atoms [29][30][31][32][33][34]. The large spin degrees of freedom in S>1/2 systems poses a much more stringent requirement for numerical treatment compared to S=1/2 systems.…”

“…In section 3, we test its validity by a comparison with ED. We focus on the evolution of Zeeman level populations induced by dipolar interactions (relevant to experiments using both Cr [29,[31][32][33] and Er atoms [34]) and the evolution of entanglement. In section 4, we apply the GDTWA to investigate various aspects of spin dynamics: the spreading of population in a synthetic dimension and the underlying approach to thermalization, as well as the build-up of quantum entanglement.…”

Dynamics of an itinerant spin-3 atomic dipolar gas in an optical lattice

“…Ultra-cold gases provide an excellent platform to study strongly correlated out-of-equilibrium quantum matter. So far, a broad range of atomic, molecular, and optical systems [1][2][3] including trapped-ions [4][5][6][7] polar molecules [8,9], Rydberg atoms [10][11][12][13][14], magnetic atoms [15][16][17][18][19][20][21][22], and cavity QED arrays [23,24] have been used to realize quantum many-body systems with long-range interactions and to probe equilibrium properties and outof-equilibrium dynamics both in pinned and itinerant systems.…”

“…The high level of control and tunability in these simulation platforms has already resulted in numerous pioneering experiments in three dimensional optical lattices. These include studies of extended Bose-Hubbard models [16], and spin lat-tice models [28] with erbium (Er) atoms using S = 6 bosonic and F = 19/2 fermionic isotopes respectively, as well as the spin dynamics of S = 3 bosonic chromium ( 52 Cr) atoms in both the superfluid and the Mott insulator regimes [15,[17][18][19].…”

Dissipative cooling of spin chains by a bath of dipolar particles

“…Subjecting the various many-body systems explored with cold atoms to well-controlled dissipative processes is a promising prospect to explore the diversity of these situations [5,6]. Among the many-body models implemented on ultra-cold atoms and molecules, lattice spin models have attracted a large attention [7][8][9][10][11][12][13][14][15][16][17][18]. The question of how dissipation affects them and whether it can be tuned to specific purposes emerges spontaneously in the context of excited Rydberg atoms [19][20][21][22].…”