Tunable Landau-Zener transitions in a spin-orbit-coupled Bose-Einstein condensate

Abstract

The Landau-Zener (LZ) transition is one of the most fundamental phenomena in quantum dynamics. It describes nonadiabatic transitions between quantum states near an avoided crossing that can occur in diverse physical systems. Here we report experimental measurements and tuning of LZ transitions between the dressed eigenlevels of a synthetically spin-orbit (SO) coupled Bose-Einstein condensate (BEC). We measure the transition probability as the BEC is accelerated through the SO avoided crossing, and study its dependence on the coupling between the diabatic (bare) states, eigenlevel slope, and eigenstate velocity-the three parameters of the LZ model that are independently controlled in our experiments. Furthermore, we performed time-resolved measurements to demonstrate the breaking-down of the spin-momentum locking of the spin-orbit coupled BEC in the nonadiabatic regime, and determine the diabatic switching time of the LZ transitions. Our observations show quantitative agreement with the LZ model and numerical simulations of the quantum dynamics in the quasimomentum space. The tunable LZ transition may be exploited to enable a spin-dependent atomtronic transistor.

Properties of spin–orbit-coupled Bose–Einstein condensates

“…The Washington State University (WSU) group investigated the physics of the ZB effect in 87 Rb [21], realized the Dicke model and the Dicke phase transition [22], measured the collective excitation spectrum (indicating the existence of roton-like structures) [23], and demonstrated the lack of Galilean invariance in SOC systems by measuring dynamical instabilities of a BEC in a moving optical lattice [24]. The Purdue group used a SOC 87 Rb BEC to study the physics of Landau-Zener tunneling [25] and to implement interferometry by periodically modulating the power of the laser beams that generate SOC [26]. Finally, the Institute of Physics (IOP) group in Beijing generated SOC in a BEC of 87 Rb atoms by modulating magnetic field gradients [37].…”

“…To set the stage, we will first briefly describe the experimental approaches to generate SOC [9,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][31][32][33][34][35].…”

Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate

“…The Raman dressing scheme in our experiment is based on coupling two hyperfine states along the x-direction. The two states play the role of (pseudo-)spins so that the BEC resembles an effective spin-1/2 system with spinorbit coupled Hamiltonian [6][7][8][9][10][11] …”

Fulde-Ferrell Superfluids without Spin Imbalance in Driven Optical Lattices

“…In 1D, the parameter region for FFLO states could be large, but the quantum fluctuation is strong [7,12,14]. The recently proposed schemes using spin-orbit coupling and in-plane Zeeman field in a 3D Fermi gas may potentially overcome these obstacles [15][16][17][18][19][20][21] in principle, but they face practical experimental issues such as the large spontaneous photon emission from the near-resonant Raman lasers [22][23][24][25][26][27][28][29][30][31] and the strong three-body loss at Feshbach resonance in the presence of spin-orbit coupling [23][24][25][26].In this Letter, we propose a new route for realizing FF superfluids in ultracold Fermi gases without involving population imbalance of two spin states that interact for generating Cooper pairing. Instead, we induce an asymmetric Fermi surface for the generation of FF states by other means and the populations of the two spins are fully equal.…”

“…The generated FF state is thermodynamically much more stable than the spin-imbalanced Fermi gas. Compared to the spin-orbit coupled schemes [15][16][17][18][19][20][21] that require near resonant Raman lasers [23][24][25][26][27][28][29][30][31], all lasers used here are fardetuned, therefore the proposed scheme should work for all types of fermionic atoms, including 6 Li [14]. Furthermore, because the hyperfine spins are not coupled with the momentum, the s-wave scattering interaction should be the same as regular Fermi gases without significant three-body loss at Feshbach resonance.…”