Control of a magnetic Feshbach resonance with laser light

Abstract

The capability to tune the strength of the elastic interparticle interaction is crucial for many experiments with ultracold gases. Magnetic Feshbach resonances 1,2 are widely harnessed for this purpose, but future experiments 3-8 would benefit from extra flexibility, in particular from the capability to spatially modulate the interaction strength on short length scales. Optical Feshbach resonances 9-15 do offer this possibility in principle, but in alkali atoms they induce rapid loss of particles due to light-induced inelastic collisions. Here, we report experiments that demonstrate that light near-resonant with a molecular bound-to-bound transition in 87 Rb can be used to shift the magnetic field at which a magnetic Feshbach resonance occurs. This enables us to tune the interaction strength with laser light, but with considerably less loss than using an optical Feshbach resonance.Using light to change the s-wave scattering length a in ultracold gases offers more flexibility than a magnetic Feshbach resonance because it is possible to apply an almost arbitrary spatial pattern of light using holographic masks. The light intensity can vary on a length scale of typically one optical wavelength and the pattern can also be varied rapidly in time. This could be used for a variety of applications, such as the simulation of the physics of black holes 3,4 , the controlled creation of solitons 5 , studies of the collapse of a Bose-Einstein condensate (BEC) in an unusual regime 6 and the simulation of certain Hamiltonians in which the scattering length needs to be different at different sites of an optical lattice 7,8 . Moreover, if each lattice site contains exactly two atoms 16 and a is varied only on every second lattice site, one could associate molecules at every second lattice site by ramping the magnetic field across the Feshbach resonance, thus producing a quantum state that resembles that of a supersolid. Another possible application for the manipulation of a with light exists in gases consisting of a mixture of different species or spin states. It would be desirable to tune the various scattering lengths in such systems independently, but for that purpose more control parameters than just the magnetic field are needed. Furthermore, if a spatially random light intensity pattern is applied, the scattering length would vary randomly with position, which might give rise to new quantum phases of the atomic gas.A known scheme to manipulate a using light uses a photoassociation resonance, sometimes also called an optical Feshbach resonance. But so far, photoassociation resonances have rarely been used to tune a because they induce rapid loss of particles. The experiments in refs 12, 13 both demonstrated a change of Re(a)/a bg − 1 ∼ ±1 in 87 Rb, where a bg is the background value of a. For these parameters, both experiments incurred losses characterized by a two-body rate coefficient K 2 with an estimated value of ∼10 −10 cm 3 s −1 . Typical densities of the order of 10 14 cm −3 result in lifetimes of the order of 100 µs...

Many-body localization in system with a completely delocalized single-particle spectrum

“…Optical Feshbach resonances are known to incur excess heating due to spontaneous emission from the excited state, and that could be detrimental for realizing many-body localization. To mitigate this effect, we suggest to use a scheme in which the light couples the bound Feshbach molecular state to an excited molecular state off-resonantly [42,43]. Using this scheme the heating time can be as long as 10ms [44], which is about 50t −1 h [9].…”

“…[3,27]. We proposed a realization of this model in cold atom experiments using spatially resolved optical Feshbach resonances [42,43]. In this model, many-body localization follows from fragmentation of particles into slow and fast species (doublons and singlons), which is a result of the strong interactions.…”

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.…”

Casting New Light on Atomic Interactions

“…Efforts toward achieving OFR in quantum gases have made significant progress [15][16][17][18][19][20][21][22][23][24][25][26][27][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.…”

“…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.…”