Spin dynamics in a two-dimensional quantum gas

Abstract

We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anticorrelated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with nonlocal Einstein-Podolsky-Rosen entanglement. Since the optical trapping of Bose-Einstein condensates (BECs) enabled the investigation of quantum gases with multiple spin components, spinor condensates have become a particularly rich research field [1,2]. While initial work focused on an understanding of the ground state and dynamical properties of spinor condensates [3][4][5], recent experiments have started to exploit their properties for applications in other fields. In particular, the production of entangled states through spin dynamics [6,7] has spawned interest in spin dynamics for their applications in precision metrology [8,9].Spin dynamics in a trapped quantum gas is strongly influenced by the geometry of the confining potential. In particular, highly asymmetric optical traps provide a way to reduce the dimensionality of a trapped quantum gas, both with respect to the motional and spin degrees of freedom [10]. Thus, tailored confining potentials offer new avenues for exploiting spin dynamics, e.g., the generation of correlated pairs of atoms in well-defined motional states [11], similar to work on four-wave mixing of ultracold atoms in an optical lattice [12][13][14].In this Rapid Communication, we investigate spin dynamics in a quantum gas confined to two dimensions (2D) by an optical lattice. We show how the spin excitation modes in the 2D potential lead to ring-shaped density distributions with a superimposed angular density modulation in time-of-flight images. The angular structure is traced to the matter-wave interference between multiple spin excitation modes with angular momentum. The observed density distributions may also be interpreted as several wave packets propagating in 2D with well-defined momentum.We investigate spin dynamics in a 87 Rb BEC prepared in |F = 2,m F = 0 (|0 ). By making several standard approximations to treat atomic collisions at ultralow temperatures, one finds that only collisions that preserve the total magnetization can occur [1]. Thus, the spin dynamics leads to scattering into |F = 2,m F = ±1 (|±1 ) and |F = 2,m F = ±2 (|±2 ), but for short evolution times, scattering between |0 and |±1 predominates; i.e., |0 + |0 ↔ |1 + |−1 . By treating the |0 condensate as a classical field ψ 0 and |±1 as small fluctuations δψ ±1 , the dynamics may be describedρ is the radial coordinate, ω ρ is the radial trapping frequency of the confining potential, and M is the mass. The 2D interacti...

Antiferromagnetic Spinor Condensates in a Two-Dimensional Optical Lattice

“…These include constructing a novel quantum-phase-revival spectroscopy driven by a competition between spin-dependent and spin-independent interactions, understanding quantum magnetism, directly detecting spin-dependent three-body and higher-body interactions, and realizing massive entanglement [1,3,22]. However, dynamics of latticetrapped spinor BECs have remained to be less explored, and most of such experimental studies have been carried out in ferromagnetic 87 Rb spinor BECs [23][24][25][26].…”

“…These include constructing a novel quantum-phase-revival spectroscopy driven by a competition between spin-dependent and spin-independent interactions, understanding quantum magnetism, directly detecting spin-dependent three-body and higher-body interactions, and realizing massive entanglement [1,3,22]. However, dynamics of latticetrapped spinor BECs have remained to be less explored, and most of such experimental studies have been carried out in ferromagnetic 87 Rb spinor BECs [23][24][25][26].In this paper, we experimentally demonstrate that a two-dimensional (2D) optical lattice can conveniently tune spin dynamics and map the phase diagram of F =1 antiferromagnetic spinor BECs. We find that the properties of spinor BECs remain largely unchanged in the presence of a shallow lattice, while a sufficiently deep lattice introduces some interesting changes.…”

A simple laser locking system based on a field-programmable gate array

“…A series of beat measurements was performed with two other lasers of similar design and wavelength. Those lasers are currently in use for the production of 87 Rb Bose-Einstein condensates 25 and locked using home-built analog PID controllers acting on a locking signal derived from a 10 MHz modulation of the laser current. For these measurements, all lasers were locked to the crossover peak of 87 Rb and acousto-optical modulators were used to shift each pair of lasers to be separated in frequency by ≈ 30 MHz.…”

Exploring the thermodynamics of spin-1 Bose gases with synthetic magnetization

“…Collisions between the different internal states of the atoms allow spin-changing collisions that have been studied in detail in [7][8][9][10]. These collisions can notably be employed to generate spin squeezing [11][12][13], that can be used to overcome the quantum shot noise limit [14][15][16][17][18]. Spinor dynamics was also studied in two dimensional systems [15], and in the presence of periodic potentials and across the superfluid to Mott insulator transition [19].…”