Dynamics and Excitations of Spin-Orbit-Coupled Bose-Einstein Condensates

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Quantum many-body interactions are responsible for material properties such as magnetism and conductivity. Understanding how these properties depend on a material's structure, its temperature, and the motion of electrons in the material is important for developing new technologies, for example those using superconductivity or "spintronics". This project will investigate many-body interactions in model systems using ultracold atoms in synthetic potentials generated by laser light. Lasers will couple the motion and "spin" of atoms, to cause spin-orbit-coupling (SOC) analogous to the relativistic SOC effects that are important in many electronic materials. This project will focus on the experimental studies of how SOC affects quantum transport phenomena and collective excitations in an atomic Bose-Einstein condensate (BEC). A BEC is a coherent superfluid phase that occurs at sufficiently low temperatures in a quantum gas. Understanding how SOC affects spin transport in BEC will provide helpful guidance for designing novel "spintronic" devices that aim to use spin (quantum mechanical angular momenta) to carry and process information with much higher efficiency and lower energy consumption than current charge-based electronics. The study will lead to new insights that will help scientists understand and discover new types of superfluids and superconductors in which the interaction of particles of different spins are important. This project will also enhance collaborations between this experimental group and several theorists active in the field, and train students in physics and engineering to participate in interdisciplinary research involving atomic physics, quantum physics, condensed matter physics, and optics.This experimental research program will study an atomic (Rb-87) Bose-Einstein condensate (BEC) subject to optically (Raman) generated synthetic gauge fields and spin-orbit coupling (SOC). The study will focus on quantum dynamics, transport and excitations in spin-orbit-coupled (SOC) BEC. The study builds upon the team's recent achievements including the demonstration of a tunable Landau-Zener transition between the dressed bands in SOCBEC, and the realization of the Landau-Zener- Stueckelberg interference (atom interferometry in quasi-momentum space) and a new type of SOC with novel spin-momentum locking using "2nd generation dressed bands" induced by modulated Raman coupling. The current program will study in particular various spin-dependent transport and excitations. One example is the "spin dipole mode" (alternating spin current) that can be used to probe not only the spin transport but also collisions and thermalization of SOCBEC in the presence of such collective excitations. Another example is the so called scissors mode and spin-scissors mode that can be used to probe superfluidity and how it may be modified by SOC and synthetic magnetic fields. The later part of the program will also investigate low-dimensional (especially 1D) SOC BEC by adding an optical lattice, where the SOC is expected to have even more pronounced effects (such as to alter the ground state, interactions and excitations). This work may provide insights to engineer new states of matter (topological phases, novel superfluids) and to understand the spin transport and dynamics in SOC systems, which are important in spintronics.