Formation of high-density cold molecules via electromagnetic trap

Preparation and control of cold molecules are advancing rapidly, motivated by many exciting applications ranging from tests of fundamental physics to quantum information processing. Here, we propose a trapping scheme to create high-density cold molecular samples by using a combination of electric and magnetic fields. In our theoretical analysis and numerical calculations, a typical alkaline-earth monofluoride, MgF, is used to test the feasibility of our proposal.A cold MgF molecular beam is first produced via an electrostatic Stark decelerator and then loaded into the proposed electromagnetic trap, which is composed of an anti-Helmholtz coil, an octupole, and two disk electrodes. Following that,a huge magnetic force is applied to the molecular sample at an appropriate time, which enables further compressing of the spatial distribution of the cold sample. Molecular samples with both higher number density and smaller volume are quite suitable for the laser confinement and other molecular experiments such as cold collisions in the next step.

A crossed focused vortex beam with application to cold molecules

We report the generation of a crossed,focused,optical vortex beam by using a pair of hybrid holograms,which combine the vortex phase and lens phase onto a spatial light modulator.We study the intensity distributions of the vortex beam in free propagation space,and the relationship of its dark spot size with the incident Gaussian beam’s waist,the lens’s focal length,and its orbital angular momentum.Our results show that the crossed,focused,vortex beam’s dark spot size can be as small as 16.3μm and adjustable by the quantum number of the orbital angular momentum,and can be used to increase the density of trapped molecules.Furthermore,we calculate the optical potential of the blue-detuned,crossed vortex beam for MgF molecules.It is applicable to cool and trap neutral molecules by intensity-gradient-induced Sisyphus cooling,as the intensity gradient of such vortex beam is extremely high near the focal point.

Theoretical derivation and simulation of a versatile electrostatic trap for cold polar molecules

We propose a versatile electrostatic trap scheme using several charged spherical electrodes and a bias electric held.We hrst give the two-ball scheme and derive the analytical solution of the electric held.In order to make a comparison,we also give the numerical solution calculated by the hnite element software(Ansoft Maxwell).Considering the loading of cold polar molecules into the trap,we give the three-ball scheme.We hrst give the analytical and numerical solutions of the distribution of the electric held.Then we simulate the dynamic process of the loading and trapping cold molecules using the classical Monte Carlo method.We analyze the influence of the velocity of the incident molecular beam and the loading time on the loading efficiency.After that,we give the temperature of the trapped cold molecules.Our study shows that the loading efficiency can reach 82%,and the corresponding temperature of the trapped molecules is about 24.6 mK.At last,we show that the single well divides into two ones by increasing the bias electric held or decreasing the voltages applied to the spherical electrodes.

AC magnetic trap for cold paramagnetic molecules

Strong-field-seeking states are the lowest-energy configurations for paramagnetic molecules in the magnetic field.Molecules in strong-field-seeking states cannot be trapped in a magnetostatic field because a magnetostatic maximum in free space is not allowed.In this paper,we propose an AC magnetic trap composed of two pairs of Helmholtz coils.The spatial magnetic field distribution is numerically calculated and the time-sequential control is depicted.We investigate the influence of the switching frequency and the electric current in the coils on the performance of our trap.Variations of the location and phase-space distribution during a whole switching cycle are simulated.Finally,we study the impact of time during which the field is switched off on the number of captured molecules in a switching cycle.

Disassociation of a one-dimensional cold molecule via quantum scattering

Motivated by the recent experimental developments in ultracold molecules and atoms,we propose a simple theoretical model to address the disassociation,reflection,and transmission probability of a one-dimensional cold molecule via quantum scattering.First,we show the Born approximation results in the weak interaction regime.Then,by employing the Lippmann-Schwinger equation,we give the numerical solution and investigate the disassociation’s dependence on the injection momentum and the interaction strengths.We find that the maximum disassociation rate has a limit when increasing the interaction strengths and injection momentum.We expect that our model can be realized in experiments in the near future.

Saturated absorption spectroscopy of buffergas-cooled Barium monofluoride molecules

We report an experimental investigation on the Doppler-free saturated absorption spectroscopy of buffer-gas-cooled Barium monofluoride(BaF)molecules in a 4 K cryogenic cell.The obtained spectra with a resolution of 19 MHz,much smaller than previously observed in absorption spectroscopy,clearly resolve the hyperfine transitions.Moreover,we use these high-resolution spectra to fit the hyperfine splittings of excited A(v=0)state and find the hyperfine splitting of the laser-cooling-relevant A^(2)Π_(1/2)(v=0,J=1/2,+)state is about 18 MHz,much higher than the previous theoretically predicted value.This provides important missing information for laser cooling of BaF molecules.

A driven three-dimensional electric lattice for polar molecules

Three-dimensional(3D)driven optical lattices have attained great attention for their wide applications in the quest to engineer new and exotic quantum phases.Here we propose a 3D driven electric lattice(3D-DEL)for cold polar molecules as a natural extension.Our 3D electric lattice is composed of a series of thin metal plates in which two-dimensional square hole arrays are distributed.When suitable modulated voltages are applied to these metal plates,a 3D potential well array for polar molecules can be generated and can move smoothly back and forth in the lattice.Thus,it can drive cold polar molecules confined in the 3D electric lattice.Theoretical analyses and trajectory calculations using two types of molecules,ND3 and PbF,are performed to justify the possibility of our scheme.The 3D-DEL offers a platform for investigating cold molecules in periodic driven potentials,such as quantum computing science,quantum information processing,and some other possible applications amenable to the driven optical lattices.

Laser cooling with adiabatic passage for type-Ⅱ transitions

We extend the idea of laser cooling with adiabatic passage to multi-level type-Ⅱ transitions.We find the cooling force can be significantly enhanced when a proper magnetic field is applied.That is because the magnetic field decomposes the multi-level system into several two-level sub-systems,hence the stimulated absorption and stimulated emission can occur in order,allowing for the multiple photon momentum transfer.We show that this scheme also works on the laser-coolable molecules with a better cooling effect compared to the conventional Doppler cooling.A reduced dependence on spontaneous emission based on our scheme is observed as well.Our results suggest this scheme is very feasible for laser cooling of polar molecules.