Coherently Forming A Single Molecule In An Optical Microtrap

Based on the principle of simplicity and purity,people has achieved the goal of the preparation and manipulation of single quantum objects,such as single photons,single ions and single atoms,for the application of quantum computation,quantum simulation and precision measurements.Trapping single cold molecule is another goal that enables other applications such as few-body dynamics and controlled cold chemical reactions.Although the association of single molecules in an optical lattice has been implemented,however,the single site addressing and detection of molecules has not been demonstrated yet Trapping single molecules in an optical microtrap(tweezer)has the intrinsic advantage for single molecule detection and manipulation.In 2015,our group has demonstrated the two-atom collision dynamics in an optical microtrap and measured the hyperfine-state-dependent inelastic collision rates.Here,we demonstrate the coherent production of single cold molecules in the motional ground state from two ultracold atoms.What we have achieved are listed as following.1.Realization of the optical cooling,trapping and manipulation for two het-eronuclear rubidium atomsWe established the experimental setup for laser cooling and trapping of 87Rb and 85Rb atoms,and we obtained two spatially overlapped cold atoms cloud.We estab-lished a strongly focused optical system to obtain an optical microtrap with a beam waist of less than 1 μm.And we trapped a single 87Rb atom and a 85Rb atom in two traps separated by 4 μm,with a life time about 7 s.We applied the sub-Doppler cooling for the two atoms to enter into the Lamb-Dicke regime.And we initialized the hyperfine states of the two atoms with the optical pumping technique and then manipulated their states coherently with stimulated Raman transitions or microwave transitions.Utilizing a two-photon transition,we realized the coherent excitation of single 87Rb atom into a Rydberg state,which paves our way to quantum information with neutral atoms.We measured a hyperfine-state-dependent and magnetic-hyperfine-state-dependent two-atom collisions in an optical tweezer,which paves the way for the further studying of two-atom interactions and bounding of a single cold molecule.2.Realization of the ground state cooling of 87Rb and 85Rb in optical micro-trapsWe performed the Raman sideband cooling for the 87Rb and 85Rb atoms to the ground state in their traps.And we can drive the coherent transition for their motional states.The probabilities in three-dimensional ground state are both of about 90%for the two atoms.We analyzed various heating mechanism while holding the atom in the trap.And we realized the high-fidelity manipulation of the motional state of a single neutral atom after the sideband cooling.3.Proposal and Realization of the high-fidelity transfer and merging of 87Rb and 85Rb into a single trapWe analyzed the heating mechanism of the merging process for a symmetric double-well potential and analyzed the efect of the trap depth ratio on the merging process.To associate single molecules effectively,the atomic wavefunction between two atoms should be overlapped near perfectly.To this end,we proposed and realized a state-dependent transport to merge one 87Rb and one 85Rb atom into the ground state of a single trap.The wavefunction overlap has been increased by 3 orders of magnitude compared with two thermal atoms without sideband cooling.4.Measurement of the interaction and scattering lengths between 87Rb and 85Rb for different hyperfine statesWe measured the contact interaction between one 87Rb and one 85Rb atom in our deep optical tweezer.The scattering length for specific hyperfine states is deduced with an error of about 26 nm which can help to search for single molecules.Combined with Multi-channel quantum defect theory,we revealed a typically ignored phenomenon in ultracold atomic collisions:the energy dependence of quantum defect.5.Coherent production of the single 87Rb85Rb molecules in an optical micro-trapWe utilized the polarization gradient effect to drive a motional sensitive MW tran-sition.We manipulated the quantized relative motion between the two atoms with the MW transitions.Based on this,we demonstrated the coherent production of a single 87Rb85Rb molecule and observed the coherent oscillation between atomic scattering state and weakly molecular bound state,and we also manipulated the quantized motion of the single molecule.We precisely determined the scattering lengths between differ-ent hyperfine states with the measured molecular binding energy with an error of less than 20 pm.