Deceleration and trapping of polar molecules
Professor Dr. Gerhard Meijer (Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin)

Getting full control over both the internal and external degrees of freedom of molecules has been an important goal in molecular physics during the last decades. Trapped samples of neutral molecules have been created by means of buffer gas cooling in a magnetic trap, by using deceleration of a molecular beam in combination with an electrostatic trap, and by pairing cold atoms to form molecules in optical or magnetic traps.
In this presentation I will give an overview of the various experiments that we have performed over the last years to explore the possibilities of manipulating neutral polar molecules with electric fields. Arrays of time-varying, inhomogeneous electric fields have been used to reduce in a stepwise fashion the forward velocity of molecules in a beam. With this so-called “Stark decelerator”, the equivalent of a LINear ACcelerator (LINAC) for charged particles, one can transfer the high phase-space density that is present in the moving frame of a pulsed molecular beam to a reference frame at any desired velocity; molecular beams with a computer-controlled (calibrated) velocity and with a narrow velocity distribution, corresponding to sub-mK longitudinal temperatures, can be produced. These decelerated beams offer new possibilities for collision studies, for instance, and enable spectroscopic studies with an improved spectral resolution; first proof-of-principle high-resolution spectroscopic studies have been performed. These decelerated beams have also been used to load ND3 molecules and OH radicals in an electrostatic trap at a density of (better than) 107 mol/cm3 and at temperatures of around 50 mK. Trapping of vibrationally excited OH (v=1) radicals has enabled a direct measurement of the infrared radiative lifetime, benchmarking the Einstein A-coefficient in the Meinel system of OH. Ground-state molecules have been trapped in a novel AC electric field trap, decelerated molecular beams have been injected in an electrostatic storage ring, and, using micro-structured electrode arrays, a switchable mirror for neutral molecules has been constructed and tested.