It is experimentally demonstrated that a beam of neutral dipolar molecules can be efficiently decelerated with a time-varying electric field. A pulsed beam of neutral metastable CO molecules is slowed down from 225 m͞s (E kin 59 cm 21 ) to 98 m͞s (E kin 11 cm 21 ) upon passage through an array of 63 synchronously pulsed electric field stages.

The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems.

CONTENTS 1. Introduction 4829 2. Historical Overview 4829 3. Stark and Zeeman Effect 4831 3.1. Introduction 4831 3.2. General Formalism 4832 3.3. Stark Effect 4833 3.3.1. Matrix Elements of H Stark 4833 3.3.2. Matrix Elements in a Basis of Symmetrized Wave Functions 4833 3.3.3. Diatomic Molecules and (A)symmetric Tops 4833 3.3.4. HCl, OH, and YbF 4834 3.3.5. ND 3 , H 2 CO, and HDO 4835 3.3.6. Candidate Molecules for Stark Deceleration 4835 3.4. Zeeman Effect 4836 3.4.1. Matrix Elements of H Zeeman in Atoms 4836 3.4.3. The Zeeman Effect of OH (X 2 Π i ) and 16 O 2 (X 3 Σ g − ) 4837 3.4.4. Candidate Molecules for Zeeman Deceleration 4838 4. Deflection and Focusing of Molecular Beams 4838 4.1. Multipole Expansion of the Electric Field in Two Dimensions 4839 4.2. Deflection Fields 4839 4.3. Focusing Low-Field Seekers 4840 4.4. Guiding Low-Field Seekers 4841 4.5. Focusing High-Field Seekers 4842 4.6. Guiding High-Field Seekers 4843 5. Deceleration of Neutral Molecules 4843 5.1.

A polar molecule experiences a force in an inhomogeneous electric field. Using this force, neutral molecules can be decelerated and trapped. It is shown here that this can in principle be done without loss in phase-space density. Using a series of 64 pulsed inhomogeneous electric fields a supersonic beam of ammonia molecules (14 NH 3 , 14 ND 3 , 15 ND 3) is decelerated. Subsequently, the decelerated molecules are loaded into an electrostatic quadrupole trap. Densities on the order of 10 7 molecules/cm 3 at a temperature of 25 mK are obtained for 14 ND 3 and 15 ND 3 separately and simultaneously. This corresponds to a phase-space density in the trap of 2ϫ10 Ϫ13 , 50 times less than the initial phase-space density in the beam.

The motion of neutral molecules in a beam can be manipulated with inhomogeneous electric and magnetic fields. Static fields can be used to deflect or focus molecules, while time-varying fields can be used to decelerate or accelerate beams of molecules to any desired velocity. We review the possibilities that this molecular beam technology offers, ranging from ultra-high resolution spectroscopy using molecular fountains to novel crossed beam scattering experiments.

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The standard model of physics is built on the fundamental constants of nature, but it does not provide an explanation for their values, nor require their constancy over space and time.Here we set a limit on a possible cosmological variation of the proton-to-electron mass ratio m by comparing transitions in methanol observed in the early universe with those measured in the laboratory. From radio-astronomical observations of PKS1830-211, we deduced a constraint of ∆m/m = (0.0 T 1.0) × 10 −7 at redshift z = 0.89, corresponding to a look-back time of 7 billion years. This is consistent with a null result. T he standard model of particle physics, the theory describing symmetries and forces of nature at the deepest level, does not provide an intrinsic explanation for the values of the fundamental coupling constants, nor does it prohibit that the fundamental constants depend on time and space. In contrast, Einstein's equivalence principle, a basic assumption of general relativity, assumes that the laws of nature, and hence the fundamental constants are independent of a local reference system. Some cosmological scenarios aimed at explaining the fine-tuning between fundamental constants sketch an evolving mechanism, where minimally varying constants are crucial for reaching the present state of complexity in the universe (1). Theoretical approaches involving additional scalar fields have imposed bounds on varying constants through tests of the weak equivalence principle (2). In the past decade the search for small variations of dimensionless fundamental constants over cosmological time scales has become an active experimental endeavor, in particular because accurate measurements of spectral lines of atoms at high redshift have provided indication for a possible variation of the fine structure constant a, either temporally (3, 4) or spatially (5, 6).A second dimensionless fundamental constant m, representing the proton-to-electron mass ratio m p /m e , probes the cosmological evolution of the nuclear versus the electroweak sector in the standard model. A search for a possible drift of m has been made operational by comparing observations of spectral lines of the hydrogen molecule (H 2 ) in distant galaxies with accurate laboratory measurements (7). These investigations, based on observations with the world's largest optical telescopes, have yielded a limit at the level of ∆m/m < 10 −5 for look-back times of 12 billion years (8, 9).Inversion transitions of ammonia (NH 3 ) were found to be~100 times more sensitive to m-variation than H 2 transitions (10, 11). Astronomical observations of NH 3 , in the microwave or radio range of the electromagnetic spectrum, led to stringent 1s constraints at the level of (1.0 T 4.7) × 10 −7(12) and (-3.5 T 1.2) × 10 −7 (13). This has shifted the paradigm for probing m-variation from optical to radio astronomy. Here we use the extreme sensitivity of methanol (CH 3 OH) (14, 15) to probe the variation of the proton-to-electron mass ratio m over cosmic time.Methanol (Fig. 1A) is the simplest a...

We have decelerated a supersonic beam of 174YbF molecules using a switched sequence of electrostatic field gradients. These molecules are 7 times heavier than any previously decelerated. An alternating gradient structure allows us to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring the molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.