Atomic quantum gases in the strong-correlation regime offer unique possibilities to explore a variety of many-body quantum phenomena. Reaching this regime has usually required both strong elastic and weak inelastic interactions because the latter produce losses. We show that strong inelastic collisions can actually inhibit particle losses and drive a system into a strongly correlated regime. Studying the dynamics of ultracold molecules in an optical lattice confined to one dimension, we show that the particle loss rate is reduced by a factor of 10. Adding a lattice along the one dimension increases the reduction to a factor of 2000. Our results open the possibility to observe exotic quantum many-body phenomena with systems that suffer from strong inelastic collisions.

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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...

Entanglement between stationary systems at remote locations is a key resource for quantum networks. We report on the experimental generation of remote entanglement between a single atom inside an optical cavity and a Bose-Einstein condensate (BEC). To produce this, a single photon is created in the atom-cavity system, thereby generating atom-photon entanglement. The photon is transported to the BEC and converted into a collective excitation in the BEC, thus establishing matter-matter entanglement. After a variable delay, this entanglement is converted into photon-photon entanglement. The matter-matter entanglement lifetime of 100 μs exceeds the photon duration by 2 orders of magnitude. The total fidelity of all concatenated operations is 95%. This hybrid system opens up promising perspectives in the field of quantum information.