Non-equilibrium dynamics in lattice-confined antiferromagnetic spinor condensates

Abstract

A spinor Bose-Einstein condensate (BEC) is a new state of matter with both magnetic order and superfluidity. It is highly controllable especially when combining with the optical lattices. Lattice-confined spinor BEC is an ideal candidate for studying nonequilibrium quantum dynamics since it can be easily prepared far from equilibrium. In this dissertation, I present the results from our experimental studies on non-equilibrium quantum dynamics in our BEC system confined by cubic optical lattices.

The introduction part includes the background knowledge of the ground state properties of the spinor Bose gas in both the free space and the optical lattices. I explain how some of the parameters can change the behavior of the whole system. Effects of the net quadratic Zeeman energy qnet and the spin-dependent interactions c are emphasized. After we experimentally observed the first-order superfluid (SF) to Mott-insulator (MI) phase transition in the lattice confined antiferromagnetic spinor BECs with adiabatic lattice ramp, we design experiments with quantum quench process to study the non-equilibrium dynamics of the system.

The Quench-Q sequence investigates the spin-mixing dynamics of BECs in deep lattices after the spin state is prepared far from the ground state by quenching q. We observe complex spin oscillations with multiple frequencies after the quench. We analyze the spectra of the oscillations and confirm that a Rabi-type model can explain the data. The data can also be utilized to reveal atom number distributions of an inhomogeneous system, and to study transitions from two-body to many-body dynamics.

The quench-L sequence initialize the non-equilibrium dynamics by quenching the lattice depth across the SF-MI phase transition. The observed spin oscillation is therefore the first experimental study, to our knowledge, on such complicated spin-mixing dynamics. We demonstrate the dependence on the quench speed and lattice potential of the data. Fits of the spin oscillations enable precise measurements of the spin-dependent interaction, a key parameter determining the spinor physics.

Furthermore, I introduce the construction of the optical superlattice by combining a blue-detuned lattice beam with the existing cubic lattice. The state manipulations in such a system have the potential to be applied to quantum information processing. In the end I discuss the possibility of realizing quantum computer based on spinor neutral atoms in optical lattices.