Casting New Light on Atomic Interactions

Abstract

Optical control of atomic interactions in quantum gases is a long-sought goal of cold atom research. Previous experiments have been hindered by rapid decay of the quantum gas and parasitic deformation of the trap potential. We develop and implement a generic scheme for optical control of Feshbach resonances which yields long quantum gas lifetimes and a negligible parasitic dipole force. We show that fast and local control of interactions leads to intriguing quantum dynamics in new regimes, highlighted by the formation of van der Waals molecules and localized collapse of a Bose condensate. DOI: 10.1103/PhysRevLett.115.155301 PACS numbers: 67.85.-d, 03.75.Kk, 34.50.-s Spatiotemporal control of interactions should bring a plethora of new quantum-mechanical phenomena into the realm of ultracold atom research. Temporal modulation of interactions is theoretically proposed as a route for creating anyonic statistics in optical lattices [1,2] as well as new types of quantum liquids [3,4] and excitations [5][6][7]. Spatial modulation should grant access to unusual soliton behavior [8,9], controlled interfaces between quantum phases [10], stable nonlinear Bloch oscillations [11], and even the dynamics of acoustic black holes [12]. The conventional technique for controlling interactions in cold atoms, magnetic Feshbach resonance [13,14], is typically insufficient for these applications because magnetic coils are generally too large for very fast or local modulation.A promising alternative is optical control of Feshbach resonances (OFR), with which high speed, spatially resolved control of interactions can be realized. 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. Second, the change of interaction strength from OFR is often accompanied by an optical potential. This potential can result in a parasitic dipole force which dominates the dynamics when the interactions are spatially modulated [21].In this Letter we propose and implement a scheme for optically controlling interactions while maintaining a long quantum gas lifetime and negligible parasitic dipole force. With a far-detuned laser, a change of the scattering length a, which determines the interaction strength, by 180 Bohr radii (a 0 ) is only coupled with a slow radiative loss of 1.6 s −1 . This loss rate is sufficiently low to allow the BEC to remain in equilibrium. Furthermore, the laser operates at a magic wavelength to eliminate the atomic dipole potential. We apply OFR to test the response of Bose-Einstein condensates (BECs) to rapid oscillation of interactions down to the time scale of 10 ns, reaching beyond the van der Waals energy scale. Moreover, by spatially modulating the interaction strength we observe the intriguing...