Topics in Spin-Orbit Coupling in Cold Atoms and Semiconductors

Abstract

This dissertation contains a collection of topics on the spin-orbit coupling of cold atoms and semiconductors.

We first consider the effects of an optically induced spin-orbit interaction on a system of Bosonic atoms. The spin-orbit term couples the emergent pseudo-spin- 1/2 degree of freedom to momentum. The single particle energy spectrum has a low energy band with two minima at non-zero momentum. At low temperatures, a many-body system will condense into these minima. In the presence of vanishing interactions, the ground state wavefunction is found to be N00N state of "left" and "right"-moving state. An experimentally observable signature of the condensate is predicted that can be observed using time-of-flight imaging.

We then predict a bulk manifestation of the spin-Hall effect in an inhomoge- neous spin-orbit-coupled system. The phenomena is predicted in the framework of the spin diffusion equations generalized to include arbitrary Rashba and linear and cubic Dresselhaus terms. This framework shows that a bulk spin-density wave with a wavevector oriented perpendicular to an applied electric field will induce a charge-

density wave characterized by a π/2-phase shift and a non-monotonic time-varying amplitude. The optimal values of spin-orbit coupling for observation of the effect are determined.

We propose a scheme for using atom interferometry to measure weak time- dependent accelerations. This proposal uses an ensemble of dilute trapped bosons with two pseudo-spin states coupled to a synthetic magnetic field, but with opposite effective charges. The synthetic field acts to couple spin to momentum continuously, which continuously imparts the acceleration on the phase of the internal states. We use time reversal pulses to reduce noise. The sensitivity of such a system is estimated

to be S ∼ 10−7 m/s^2/√Hz

Finally, we consider the semiclassical dynamics of a trapped spin-orbit coupled system. We find non-linear dynamics parameterized by the value of the initial displacement of the trap, and the anisotropy of the spin-orbit energy spectrum. We show that the dynamics can give a Berry's phase, and propose an experiment to measure this phase. We then propose a generalization of the 4-level scheme that allows for spin-orbit coupling described by a vector potential that is proportional to the angular momentum operator.