Trapping polar molecules in an ac trap

Abstract

Polar molecules in high-field seeking states cannot be trapped in static traps as Maxwell's equations do not allow a maximum of the electric field in free space. It is possible to generate an electric field that has a saddle point by superposing an inhomogeneous electric field to an homogeneous electric field. In such a field, molecules are focused along one direction, while being defocused along the other. By reversing the direction of the inhomogeneous electric field the focusing and defocusing directions are reversed. When the fields are being switched back and forth at the appropriate rate, this leads to a net focusing force in all directions. We describe possible electrode geometries for creating the desired fields and discuss their merits. Trapping of 15 ND 3 ammonia molecules in a cylindrically symmetric ac trap is demonstrated. We present measurements of the spatial distribution of the trapped cloud as a function of the settings of the trap and compare these to both a simple model assuming a linear force and to full three-dimensional simulations of the experiment. With the optimal settings, molecules within a phase-space volume of 270 mm 3 ͑m/s͒ 3 remain trapped. This corresponds to a trap depth of about 5 mK and a trap volume of about 20 mm 3 .

Trapping of Rb Atoms by ac Electric Fields

“…Above 72 Hz no atoms are detected. The range of working frequencies is narrow compared to that of both Paul traps for ions [8] and ac traps for polar molecules [11]. The observed frequency range is in good agreement with results from trajectory calculations.…”

“…Multipole-expansion fits to the calculated electric fields in our trap indicate that higher-order terms up to the decapole are significant. The finite octupole and decapole components result in additional forces that considerably reduce the trap depth [11].…”

“…For ground-state ammonia molecules, ac electric traps with a depth of several millikelvins have been demonstrated [9,10], and the motion of the trapped molecules has been analyzed in detail [11]. In addition, any ground-state atom or nonpolar molecule can be confined in an ac electric trap via their induced dipole moment.…”

Kalte Moleküle: Herstellung, Anwendungen und Herausforderungen

“…Diese Falle eignet sich sowohl für die Speicherung von Molekülen in tieffeld-wie auch in hochfeldsuchenden Zuständen. [120,124] Für beide gilt, dass bei niedrigen Schaltsequenzen noch keine Moleküle gespeichert werden; die Moleküle werden zu lange defokussiert bzw. fokussiert, sodass sie die Falle verlassen.…”

Why are Cold Molecules so Hot?

“…[56][57][58] Figure 17 shows schematically the electrode geometry of a cylindrical AC trap that has been used to trap both ND 3 molecules and Rb atoms. Panels (b) and (c) show the strength of the electric field along the symmetry axis (z-axis) and along the radial direction (r) when the field is focusing either along the z-axis or radially.…”