Two novel electrostatic traps named octopole-based disk electrostatic trap (ODET) and tubular-based disk electrostatic trap (TDET) are proposed for trapping cold polar molecules in low-field-seeking states. Using MgF as the target molecule, single loading and multi-loading methods are numerically simulated with varied incident velocities of slow molecular beams in the two types of traps, respectively. In ODET, with an incident velocity of 10 m/s, a highest loading efficiency of 78.4% or 99.9% has been achieved under the single loading or multi-loading operation mode. In TDET, with an incident velocity of 11 m/s, a highest loading efficiency of 81.6% or 106.5% has been achieved using the two loading methods, respectively. With such high loading efficiencies, the trapped cold molecules can be applied in the researches of cold collisions, high precision spectroscopy, and precision measurements. Especially, together with a blue-detuned hollow beam, the new electrostatic traps proposed here offer a new platform for the following gradient-intensity cooling of MgF molecules, which may provide a new way to produce high density ultracold molecules.

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The 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 proposed a trapping scheme to create high-density cold molecular samples 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 firstly 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 next step of laser confinement and other molecular experiments such as cold collisions.

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Taming more species of molecules with large density is a long-standing goal in molecular science. Heavy molecule (> 100 amu) is of particular interest for precision measurements. However, decelerating a fast-moving beam of heavy molecules to rest remains challenging for Zeeman deceleration. Additionally, the traditional approach of pulsed Zeeman decelerator suffers from serious molecular loss during deceleration, significantly limiting its potential applications. Herein, we present a ring-shaped traveling wave Zeeman decelerator (RTWZD) featured with true three-dimensional smoothly-moving magnetic potential wells that directly solve the above intractable problems. With this approach, not only the density of the molecule can be greatly increased but also the range of molecular species for Zeeman deceleration can be extended from light to heavy. The performance of the RTWZD is characterized with both the theoretical analysis and the numerical calculation, where a group of atoms and molecules such as 7Li, 32O2, 88Sr19F and 174Yb19F are employed as testers. Losses in the traditional Zeeman decelerator can be avoided, yielding more than two orders of magnitude improvement in molecular density. These characteristics of the RTWZD make it an ideal toolbox to produce cold and dense atomic/molecular samples, enabling promising prospects for cold collision, sympathetic cooling, and precision measurement.