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We propose a dynamical imprinting scheme to create nodal lines of torus and lemniscate knots via a Raman process in a dilute spinor Bose-Einstein condensate. We calculate the desired parameters and the necessary spatial profiles of the Raman laser fields that couple a realistic multilevel atomic system, and demonstrate the imprinting results via a numerical calculation. Additionally, we show the capability of our method to adjust the size and the aspect ratio of the knotted nodal lines by tuning the parameters of Raman lasers that propagate along different directions. 

We describe an experimental protocol for the creation of a three- dimensional topological defect, a skyrmion, in a pseudo-spin-1/2 Bose-Einstein condensate (BEC) confined in a spin-independent har- monic trap. We show that one can imprint the skyrmion on the BEC within a few tens of microseconds using a Raman process with the structured laser fields. We numerically solved the mean- field Gross-Pitaevskii equation to examine our imprinting scheme, and found that all parameters we use are experimentally feasible. 

We propose an experimentally feasible method to generate a one-dimensional optical lattice potential in an ultracold Bose gas system that depends on the transverse momentum of the atoms. The optical lattice is induced by the artificial gauge potential generated by a periodically driven multilaser Raman process. We study the many-body Bose-Hubbard model in an effective 1D case and show that the superfluid–Mott-insulator transition can be controlled via tuning the transverse momentum of the atomic gas. Such a feature enables us to control the phase of the quantum gas in the longitudinal direction by changing its transverse motional state.We examine our prediction via a strong-coupling expansion to an effective 1D Bose-Hubbard model and a quantum Monte Carlo calculation and discuss possible applications. 

Abstract The origin of macroscopic irreversibility from microscopically time-reversible dynamical laws—often called the arrow-of-time problem—is of fundamental interest in both science and philosophy. Experimentally probing such questions in quantum theory requires systems with near-perfect isolation from the environment and long coherence times. Ultracold atoms are uniquely suited to this task. We experimentally demonstrate a striking parallel between the statistical irreversibility of wavefunction collapse and the arrow of time problem in the weak measurement of the quantum spin of an atomic cloud. Our experiments include statistically rare events where the arrow of time is inferred backward; nevertheless we provide evidence for absolute irreversibility and a strictly positive average arrow of time for the measurement process, captured by a fluctuation theorem. We further demonstrate absolute irreversibility for measurements performed on a quantum many-body entangled wavefunction—a unique opportunity afforded by our platform—with implications for studying quantum many-body dynamics and quantum thermodynamics. 

We propose a practical protocol to generate and observe a non-Abelian geometric phase using a periodically driven Raman process in the hyperfine ground-state manifold of atoms in a dilute ultracold gas. Our analysis is based upon recent developments and application of Floquet theory to periodically driven quantum systems. The simulation results show the non-Abelian gauge transformation and the noncommuting property of the SU(2) transformation operators. Based on these results, we propose a possible experimental implementation with an ultracold dilute Bose gas.