Two-dimensional superexchange-mediated magnetization dynamics in an optical lattice

Abstract

The competition of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study non-equilibrium magnetization dynamics in an extended 2D system by loading effective spin-1/2 bosons into a spin-dependent optical lattice, and we use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a non-equilibrium anti-ferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the underlying Hamiltonian parameters associated with superexchange and tunneling. Remarkably, with tunneling off-resonantly suppressed, we are able to observe superexchange dominated dynamics over two orders of magnitude in magnetic coupling strength, despite the presence of vacancies. In this regime, the measured timescales are in agreement with simple theoretical estimates, but the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques.The interplay of spin and motion underlies some of the most intriguing and poorly understood behaviors in many-body quantum systems [1]. A well known example is the onset of superconductivity in cuprate compounds when mobile holes are introduced into an otherwise insulating 2D quantum magnet [2]; understanding this behavior is particularly challenging because the dimensionality is low enough to support strong quantum correlations, but high enough to prohibit numerical solution. Ultracold atoms in optical lattices realize tunable, idealized models of such behavior, and can naturally operate in a regime where the quantum motion (tunneling) of particles and magnetic interactions (superexchange) explicitly compete [3,4].For ultracold atoms in equilibrium, the extremely small energy scale associated with superexchange interactions makes the observation of magnetism challenging, and short-range antiferromagnetic correlations resulting from superexchange have only recently been observed [5,6]. Out of equilibrium, superexchange-dominated dynamics has been demonstrated in isolated pairs of atoms [7], in 1D systems with single atom spin impurities [8], and recently in the decay of spin-density waves [9]. However, the perturbative origin of superexchange in these systems requires that it be weak compared to tunneling, and thus the manifestation of superexchange requires extremely low motional entropy. Dipolar gases [10] and ultracold polar molecules [11] in lattices provide a promising route toward achieving large (non-perturbative) magnetic interactions [12], but, technical limitations in these systems currently complicate the simultaneous observation of motional and spin-exchange effects.Here, we study the magnetization dynamics of effective spin-1/2 bosons in a 2D optical lattice following a global quench from an initially antiferromagnetically ordered state [13]. The dynamics we observe is governed by a bosonic t-J model [14,15]. Utilizing a checkerboard optical...

Sudden expansion and domain-wall melting of strongly interacting bosons in two-dimensional optical lattices and on multileg ladders

“…Such long-range interactions arise by mapping even a short-range Hamiltonian on a 2D lattice to a 1D chain for the application of DMRG. Recent experiments have started to study the nonequilibrium dynamics of interacting quantum gases in 2D lattices or in the 1D-to-2D crossover [17,19,61]. Motivated by Refs.…”

Four-body ring-exchange interactions and anyonic statistics within a minimal toric-code Hamiltonian

“…Although a large category of manybody models [17][18][19][20][21] have been realized with optical lattices, implementing the ring-exchange Hamiltonian is notoriously difficult due to its nature of the fourth-order spin interaction, which is greatly suppressed compared to the lower order processes, such as superexchange interactions [19,20]. So, generation and observation of the ring-exchange interactions and the correlated anyonic excitations become the urgent needs for further studying their physical properties and various attractive applications.…”

Spin-dependent optical superlattice

“…Following this route, sub-lattice addressing and √ SWAP operations in double-wells (DWs) were demonstrated [10,11], where the atomic spins in decoupled DW arrays were addressed by ultilizing the spin-dependent effect [10,12]. However, extending these entangled pairs to a one-dimensional (1D) chain or a two-dimensional (2D) cluster remains challenging due to the lack of control over inter-well couplings [13]. In this context, a bichromatic lattice referred as "superlattice" provides an alternative degree of freedom to connect the entangled pairs by tuning the relative lattice phase [14,15].…”