Zhengkun Fu

Spin-Orbit Coupled Degenerate Fermi Gases

In this Letter, we report the first experimental realization and investigation of a spin-orbit coupled Fermi gas. Both spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state are observed as hallmarks of spin-orbit coupling in a Fermi gas. The single particle dispersion is mapped out by using momentum-resolved radio-frequency spectroscopy. From momentum distribution and momentum-resolved radio-frequency spectroscopy, we observe the change of fermion population in different helicity branches consistent with a finite temperature calculation, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system.

Bose-Einstein condensate in a light-induced vector gauge potential using 1064-nm optical-dipole-trap lasers

Using two crossed 1064-nm optical-dipole-trap lasers to be the Raman beams, an effective vector gauge potential for Bose-Einstein condensed 87 Rb in the F = 2 hyperfine ground state is experimentally created. The moderate strength of the Raman coupling still can be achieved when the detuning from atomic resonance is larger than the excited-state fine structure, since rubidium has 15 nm energy-level spitting. The atoms at the far detuning of the Raman coupling are loaded adiabatically into the dressed states by ramping the homogeneous bias magnetic field with different paths and the dressed states with different energies are studied experimentally. The experimental scheme can be easily extended to produce the synthetic magnetic or electric field by means of a spatial or time dependence of the effective vector potential.

Radio-frequency spectroscopy of a strongly interacting spin-orbit-coupled Fermi gas

We investigate experimentally and theoretically radio-frequency spectroscopy and pairing of a spin-orbit-coupled Fermi gas of

Optical control of a magnetic Feshbach resonance in an ultracold Fermi gas

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Observation of Collective Atomic Recoil Motion in a Degenerate Fermion Gas

K atoms near a Feshbach resonance at

Transport of Bose-Einstein condensate in QUIC trap and separation of trapping spin states

{B}_{0}=202.2

Momentum-resolved Raman spectroscopy of bound molecules in ultracold Fermi gas

G. Experimentally, the integrated spectroscopy is measured, showing characteristic blue and red shifts in the atomic and molecular responses, respectively, with increasing spin-orbit coupling. Theoretically, a smooth transition from atomic to molecular responses in the momentum-resolved spectroscopy is predicted, with a clear signature of anisotropic pairing at and below resonance. Our many-body prediction agrees qualitatively well with the observed spectroscopy near the Feshbach resonance.

Evaporative cooling of 87 Rb atoms into Bose-Einstein condensate in an optical dipole trap

We use laser light near resonant with a molecular bound-to-bound transition to control a magnetic Feshbach resonance in ultracold Fermi gases of 40 K atoms. The spectrum of excited molecular states is measured by applying a laser field that couples the ground Feshbach molecular state to electronically excited molecular states. Nine strong bound-to-bound resonances are observed below the 2 P1/2 + 2 S1/2 threshold. We use radio-frequency spectroscopy to characterize the laser-dressed bound state near a specific bound-to-bound resonance and show clearly the shift of the magnetic Feshbach resonance using light. The demonstrated technology could be used to modify interatomic interactions with high spatial and temporal resolutions in the crossover regime from a Bose-Einstein condensate to a Bardeen-Cooper-Schrieffer superfluid.

Spin-Orbit Coupling Induced Coherent Production of Feshbach Molecules in a Degenerate Fermi Gas

We demonstrate collective atomic recoil motion with a dilute, ultracold, degenerate fermion gas in a single spin state. By utilizing an adiabatically decompressed magnetic trap with an aspect ratio different from that of the initial trap, a momentum-squeezed fermion cloud is achieved. With a single pump pulse of the proper polarization, we observe, for the first time, multiple wave-mixing processes that result in distinct collective atomic recoil motion modes in a degenerate fermion cloud. Contrary to the case with Bose condensates, no pump-laser detuning asymmetry is present.

Momentum-resolved Raman spectroscopy of a noninteracting ultracold Fermi gas

We have studied the locomotion track of (87)Rb Bose-Einstein condensate during decompressing the trap into the center of the glass cell in a quadrupole-Ioffe configuration trap. In order to change the position of the BEC, the current in the quadrupole coils is reduced while the current in the Ioffe coil keeps constant. Because of the strongly reduced trap frequencies of the moved trap, the BEC considerably sags down due to the gravity. Thus an inflexion point exists in the process of moving BEC. When rubidium atoms go over the inflexion point, they cannot keep in balance under the gravity and the force provided by a magnetic field, and flow downward and towards Ioffe coil. By utilizing this effect, the trapped atoms with the spin state |F = 2,mF = 1>, which are left over in the BEC, can be separated from the BEC of |F = 2,mF = 2> state.