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Chinese Physics Letters

Magnetic-Field Dependence of Raman Coupling Strength in Ultracold 40 K Atomic Fermi Gas

Lianghui Huang, Pengjun Wang, Zengming Meng, Peng Peng, Liangchao Chen, Dong‐Hao Li, Jing Zhang

Published Mar 1, 2016• 1 citation
Publisher

Abstract

We experimentally demonstrate the relation of Raman coupling strength with the external bias magnetic field in degenerate Fermi gas of 40 K atoms. Two Raman lasers couple two Zeeman energy levels, whose energy splitting depends on the external bias magnetic field. The Raman coupling strength is determined by measuring the Rabi oscillation frequency. The characteristics of the Rabi oscillation is to be damped after several periods due to Fermi atoms in different momentum states oscillating with different Rabi frequencies. The experimental results show that the Raman coupling strength will decrease as the external bias magnetic field increases, which is in good agreement with the theoretical prediction.

DOI
10.1088/0256-307x/33/3/033401

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We present a theory to derive the output rate of an atom laser consisting of an interacting Bose-Einstein condensate in a magnetic trap and two additional rf fields transferring trapped atoms to a repelled Zeeman sublevel via an intermediate untrapped Zeeman sublevel. We explicitly obtain the dependence of the output rate ${\ensuremath{\Gamma}}_{\mathrm{out}}$ on various characteristic parameters such as a coupling parameter (the Rabi frequency), the atom number density in the center of the condensate, and the strength of the atom-atom interaction.
We investigate theoretically the Raman coupling between two internal states of a trapped low-density quantum-degenerate Fermi gas. In general, the trap frequencies associated with the two internal states can be different, leading to the onset of collapses and revivals in the population difference $\ensuremath{\Delta}N$ of the two internal states. This behavior can be changed drastically by two-body collisions. In particular, we show that under appropriate conditions they can suppress the dephasing leading to the collapse of $\ensuremath{\Delta}N,$ and restore almost full Rabi oscillations between the two internal states. These results are compared and contrasted to those for a quantum-degenerate bosonic gas.
Stimulated Raman transition is generally used for a coherent population transfer in a cold atom interferometer. We have experimentally investigated the magnetic field dependence of coherent population transfer by the stimulated Raman process. Experimental data show that both Rabi frequency and population greatly depend on the amplitude and sense of the magnetic field. Theoretical analysis is also carried out, and the experimental results are in good agreement with the theoretical calculations. The study is helpful for optimizing the interferometer fringes and for improving the rotation measurement precision of a Sagnac interferometer.
Ultracold atom experiments use a gas of neutral atoms with temperatures less than 100 µK above absolute zero and offer unmatched experimental control of quantum states and coherence, which has allowed ultracold atom-based measurements to be some of the most precise to date. While ultracold atom experiments can control almost all atomic degrees of freedom, spin-dependent trapping and spatial manipulation has remained difficult if not inaccessible. We are developing a method of spin-dependent trapping and spatial manipulation for ultracold neutral atoms using the AC Zeeman force produced by a microwave magnetic near-field gradient generated by an atom chip. We measure the AC Zeeman force on ultracold rubidium atoms by observing its effect on the motion of atoms in free-fall and on those confined in a trap. We have studied the force as a function of microwave frequency detuning from a hyperfine transition at 6.8 GHz at several magnetic field strengths and have observed its characteristic bipolar and resonant features predicted by two-level dressed atom theory. We find that the force is several times the strength of gravity in our setup, and that it can be targeted to a specific hyperfine transition while leaving other hyperfine states and transitions relatively unaffected. We find that our measurements are reasonably consistent with parameter-free theoretical predictions.