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

Abstract

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 P 1/2 + 2 S 1/2 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 (BEC) to a Bardeen-Cooper-Schrieffer (BCS) superfluid.PACS numbers: 05.30. Fk, 03.75.Hh, 03.75.Ss, The ability to control the strength of interatomic interactions has led to revolutionary progress in the field of ultracold atomic gases [1]. Magnetic-field-induced Feshbach resonance is one of the such powerful tools and has been used widely in atomic gases of alkali atoms to understand strong correlation of quantum many-body systems [1]. An alternative technique for tuning interatomic interactions is optical Feshbach resonance (OFR) [2,3], in which free atom pairs are coupled to an excited molecular state by laser field near a photoassociation resonance. OFR is particularly useful for controlling interatomic interactions in atomic gases of alkali earth atoms [4][5][6][7], because of the lack of magnetic structure in the ground state of these atoms. It also offers more flexible control on the interaction strength with high spatial and temporal resolutions, since the laser intensity can be varied on short length and time scales. However, OFR often suffers from rapid loss of atoms due to the light-induced inelastic collisions between atoms. Recently, optical lasers in combination with magnetic Feshbach resonances have been developed to modify the interatomic interaction in a Bose gas [8,9] atoms and have been shown to reduce the loss rate by an order of magnitude compared with the ordinary OFR in 87 Rb [8,10]. In this Letter, we demonstrate the realization of such a laser-controlled magnetic Feshbach resonance in a strongly interacting Fermi gas of 40 K atoms. Strongly interacting atomic Fermi gas is a clean and easily controllable system with rich and intriguing physical properties [11,12]. It provides a new platform for solving some challenging problems in condensed matter physics and for quantum simulating novel exotic quantum states of matter, such as the high-temperature superconductivity and BEC-BCS crossover [13]. Magnetic Feshbach resonance has already been shown to play a key role in exploring strongly interacting Fermi gases with balanced or imbalanced spin-populations, leading to the creation of molecules [14][15][16][17], realization of fermionic superfluidity [18][19][20][21][22] and discovery of fermionic universality [23][2...

Casting New Light on Atomic Interactions

“…Assuming the molecular and atomic magnetic moments differ μ m ≠ 2μ a , the vector light shift can bring the molecular states closer to the scattering state, inducing a resonant atom-molecule coupling. Optical shifts of a magnetic Feshbach resonance have been observed using specific bound-to-bound transitions [25][26][27][28] and recently using a far-detuned laser [38]. Since our scheme does not rely on proximity to any atomic or molecular transitions, the lifetime is only limited by the one-body off-resonant scattering rate.…”

“…Efforts toward achieving OFR in quantum gases have made significant progress [15-28] but have encountered two major obstacles. First, in previous experiments OFR has limited the quantum gas lifetime to the millisecond time scale [24,26,27] due to optical excitation to molecular states. Short lifetimes forbid studies of quantum gases in equilibrium or after typical dynamical time scales.…”

Quantification of the memory effect of steady-state currents from interaction-induced transport in quantum systems

“…A spatial interaction imbalance can be produced experimentally by nonuniform magnetic field [95,96], or optical control of the atomic collisions [97][98][99][100][101][102][103]. Ref.…”

Tuning Feshbach resonances in cold atomic gases with interchannel coupling

“…Previous studies have shown that FRs can be modified either by dressing the molecular bound state in the closed channel [2][3][4][5][6][7][8][9], or by coupling different atomic states in the open channel [10][11][12][13][14]. Under these situations, the resonance position as well as the atomic scattering length can be tuned by additional parameters.…”