Studies of Non-Equilibrium Quantum Phenomena in a Momentum-Space Bose-Einstein Condensate

Colby Schimelfenig

This dissertation documents my work in the Engels group to study quantum phenomena in a spin-orbit coupled (SOC) Bose-Einstein condensate (BEC). In particular, I describe and mark the experimental observation of three highly sought after physical effects: First, the formation of a momentum space Josephson junction and the related measurement of the a.c. Josephson effect, as well as the zero-quasimomentum band gap corresponding to a pseudo-Goldstone mode; second, macroscopic quantum self-trapping (MQST) and a related dynamical phase transition (DPT) based on the reported MQST; and third, the observation of adiabatic scaling of spin dynamics when ramping through a phase transition that will lay the foundation for future exploration of scaling dynamics due to the Kibble-Zurek mechanism (KZM). In order to study these three phenomena, we employ a BEC with SOC induced by a Raman laser system. A defining feature of the SOC system is its two spin-momentum eigenstates. We enhance the coupling between these eigenstates by adding a stationary optical lattice. To study Josephson effects, we control the Raman laser frequency detuning, quenching it from a high value to a low value in order to induce both Josephson and plasma oscillations. Bragg spectroscopy is used to measure the pseudo-Goldstone mode gap. MQST is observed by slowly ramping the Raman detuning across a phase transition and remarking on the spin dynamics of the system. By tuning the optical lattice strength the system enters either a self-trapping or a delocalized mixed state regime. A MQST based DPT is then engineered by quenching the Raman detuning and measuring the spin state oscillations that occur afterwards at a fixed optical lattice strength. Long-time scale non-analytic features in a systems dynamics are defining characteristic of a DPT. By measuring the time averaged spin-populations of the SOC system we detect the presence of a DPT. To observe scaling dynamics within the SOC and optical lattice system, we ramp the optical lattice strength from a high to low value and measure the relative spin-populations of the system during the ramp. The change of the spin-populations give us a time factor that we use to characterize the system. The work done measuring this scaling will act as a stepping stone to further develop the techniques that will be used to measure universal scaling in the SOC and optical lattice system due to the KZM. These studies, as a group, mark an interesting set of experiments done measuring the dynamics of non-equilibrium systems. They are all topics of study that have many varied applications. The SOC + stationary optical lattice system is very rich and offers many possible areas of research in the future.

Studies of Non-Equilibrium Quantum Phenomena in a Momentum-Space Bose-Einstein Condensate

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