Boudewijn J Verhaar

• Prof Dr
• Eindhoven University of Technology

Experiments involving ultracold molecules require sufficiently long lifetimes, which can be very short for excited rovibrational states in the molecular potentials. For alkali-metal atoms such as rubidium, a lowest rovibrational molecular state can both be found in the electronic singlet and triplet configurations. The molecular singlet ground stat...

Experiments involving ultracold molecules require sufficiently long lifetimes, which can be very short for excited rovibrational states in the molecular potentials. For alkali atoms such as rubidium, molecular, rovibrational ground-states can both be found in the electronic singlet and triplet configurations. The molecular singlet ground state is a...

Ultracold atoms are increasingly used for high precision experiments that can be utilized to extract accurate scattering properties. This calls for a stronger need to improve on the accuracy of interatomic potentials, and in particular the usually rather inaccurate inner-range potentials. A boundary condition for this inner range can be convenientl...

The scattering length is commonly used to characterize the strength of ultracold atomic interactions, since it is the leading parameter in the low-energy expansion of the scattering phase shift. Its value can be modified via a magnetic field, by using a Feshbach resonance. However, the effective range term, which is the second parameter in the phas...

Since the first realizations of Bose-Einstein condensates in ultracold atomic gases in 1995, the 85Rb and 87Rb atomic species have acted as the workhorses of experimental developments in this field. Parallel to and partly preceding this work the same isotopes figured also as workhorses for successful theoretical attempts aiming at unravelling the n...

Ultracold molecules can be associated from ultracold atoms by ramping the magnetic field through a Feshbach resonance. A reverse ramp dissociates the molecules. Under suitable conditions, more than one outgoing partial wave can be populated. A theoretical model for this process is discussed here in detail. The model reveals the connection between t...

The properties of Feshbach resonances are commonly described by a single-resonance Feshbach model, and open-channel resonances are not taken into account explicitly. However, an open-channel resonance near threshold limits the range of validity of this model. Such a situation is created when the background scattering length is much larger than the...

Feshbach resonances are commonly described by a single-resonance Feshbach model, and open-channel resonances are not taken into account explicitly. However, an open-channel resonance near threshold limits the range of validity of this model. Such a situation exists when the background scattering length is much larger than the range of the interatom...

In this paper we investigate the effective scattering length $a$ of spin-polarized Ne*. Due to its anisotropic electrostatic interaction, its scattering length is determined by five interaction potentials instead of one, even in the spin-polarized case, a unique property among the Bose condensed species and candidates. Because the interaction poten...

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a three-level...

Radio-frequency techniques were used to study ultracold fermions. We observed the absence of mean-field "clock" shifts, the dominant source of systematic error in current atomic clocks based on bosonic atoms. This absence is a direct consequence of fermionic antisymmetry. Resonance shifts proportional to interaction strengths were observed in a thr...

More than 40 Feshbach resonances in rubidium 87 are observed in the magnetic-field range between 0.5 and 1260 G for various spin mixtures in the lower hyperfine ground state. The Feshbach resonances are observed by monitoring the atom loss, and their positions are determined with an accuracy of 30 mG. In a detailed analysis, the resonances are iden...

A cloud of 87Rb atoms in the |f, mf>= |1, -1> ground state was evaporatively cooled in a Ioffe-Pritchard trap close to or below the BEC transition temperature. The atoms were then transferred into an optical dipole trap made of an Yb:YAG laser operating at a wavelength of 1030 nm. After turning off the magnetic trap, an RF pulse transferred the ato...

More than 40 Feshbach resonances in rubidium 87 are observed in the magnetic field range between 0.5 and 1260 G for various spin mixtures in the lower hyperfine ground state. The Feshbach resonances are observed by monitoring the atom loss, and their positions are determined with an accuracy of 30 mG. In a detailed analysis, the resonances are iden...

We demonstrate a Rb fountain clock which has a small cold collision shift that is cancelled by detuning the microwave cavity. To further enhance the stability and accuracy, we are currently developing a new state detection technique that directly measures population differences and are juggling atoms in the fountain. Fountain clocks also enable a n...

Combining the measured binding energies of four of the most weakly bound rovibrational levels of the 87Rb2 molecule with results of two other recent high-precision experiments, we obtain exceptionally strong constraints on the atomic interaction parameters in a highly model independent analysis. The comparison of (85)Rb and (87)Rb data, where the t...

We demonstrate a Rb fountain clock which has a small cold collision shift that is cancelled by detuning the microwave cavity. We also demonstrate a juggling Rb clock and propose a novel quantum atom-optics precision scattering measurement for a juggling atomic clock. Finally we describe the design concept for RACE, a microgravity Rb clock for the I...

We propose and analyze an approach to convert an atomic condensate into a condensate of diatomic molecules in the rovibrational ground state. The process consists of a stimulated Raman transition dramatically enhanced by a time-dependent magnetic field that sweeps over a field-induced Feshbach resonance. For a condensate of Na atoms a judicious cho...

We propose and analyze an approach to convert an atomic condensate into a condensate of diatomic molecules in the rovibrational ground state. The process consists of a stimulated Raman transition dramatically enhanced by a time-dependent magnetic field that sweeps over a field-induced Feshbach resonance. For Na atoms the Raman transition probabilit...

We describe a method that is well suited to analysis of the bound states of the alkali-metal dimers near their dissociation limit. The method combines inverse perturbation theory, coupled-channel bound-state theory, and the accumulated phase method to treat the short-range part of the molecular potentials. We apply this method to analyze the bound-...

We study Feshbach resonance scattering in a time-dependent magnetic field. We explain the extremely rapid decay observed in a recent experiment investigating Feshbach resonances in a Na Bose-Einstein condensate. In our picture, the decay is stimulated by the formation of a molecular condensate of quasibound atom pairs. Another essential element is...

We extract information about collisions of ultra-cold ground-state rubidium atoms from observations of a g-wave shape resonance in the system via time-independent and time-dependent photoassociation. The shape resonance arises from a quasi-bound state inside a centrifugal barrier that enhances the excitation to the bound electronically excited stat...

The concepts of scattering length (a) and effective range (re) are introduced in two dimensions for an isotropic finite-range potential. Application to mutual scattering of pairs of hydrogen atoms in the triplet state adsorbed at a liquid helium surface shows the usefulness of a description in terms of two parameters. The values derived for this ca...

We review the information on the interactions between cold ground-state Na atoms following from Na2 bound states, a Na photoassociation experiment, and a recent observation of field-induced Feshbach resonances in a Na Bose condensate. We obtain a set of Na interaction parameters that is in excellent agreement with all these experimental data. The e...

We have loaded spin-polarized hydrogen (SPH) into a magnetostatic Ioffe trap with central fields as high as 1 T and at two different temperatures, 0.25 and 0.4 K, on the way to create a gas of SPH with two distinguishable Bose component. We have measured the magnetic dipole decay rate constant of SPH at these high fields and found good agreement wi...

The recent success of BEC in rubidium, lithium and sodium has led us to reinvestigate the collisional properties of cesium, that define the circumstances for BEC. We analyze a set of cold-collision data, comprising atomic fountain frequency shifts and elastic scattering rates, to determine phase parameters that completely characterize cold collisio...

We probe s-wave collisions of laser-cooled 85Rb\( f = 2,mf = -2\) atoms with Zeeman-resolved photoassociation spectroscopy. We observe that these collisions exhibit a magnetically tunable Feshbach resonance, and determine that this resonance tunes to zero energy at a magnetic field of 164+/-7 G. This result indicates that the self-interaction energ...

This paper investigates the possibility of suppressing the ionization rate in a magnetostatic trap of metastable neon atoms by spin-polarizing the atoms. Suppression of the ionization is critical for the possibility of reaching Bose-Einstein condensation with such atoms. We estimate the relevant long-range interactions for the system, consisting of...

We investigate theoretically the influence of magnetically tunable Feshbach collision resonances on the photoassociation spectra of ultracold atoms. As an example we consider recently predicted resonances for 85Rb atoms. For excitation to the 85Rb2 0-g(S1/2+P1/2) electronic state, we predict that the photoassociation rate is resonantly enhanced by...

We apply a simplified description to weakly bound states and cold-collision continuum states of pairs of ground-state alkali-metal atoms, which complements the usual more elaborate coupled-channel treatment. It is based on a diabatic treatment of the transition region between the exchange-dominated interatomic distance range at small r and the hype...

We examine the long-range part of the rare-gas diatomic potentials that connect to the R{(n-1)p5ns}+R{(n-1)p5np} atomic states in the separated atom limit (n=3, 4, 5, and 6 for Ne, Ar, Kr, and Xe, respectively). We obtain our potentials by diagonalization of a Hamiltonian matrix containing the atomic energies and the electric dipole-dipole interact...

In current dilute Bose condensates the collisional behaviour of alkali atoms is very important. We show that the rich behaviour of two-body collisions, including scattering lengths, Feshbach resonances and (suppressed) decay rates can almost quantitatively be accounted for in a simplified, diabatic model(J.M. Vogels, B.J. Verhaar, R.H. Blok, Phys....

The disagreement between a theoretical prediction(Moerdijk et al., Phys. Rev. A 51), 4852 (1995). for the ^23Na |f=1,m=-1> + ^23Na |f=1,m=-1> scattering length a_1,-1 based on RKR triplet and IPA singlet potentials, and a second prediction(Tiesinga et al., J. Res. Natl. Inst. Stand. Technol. 101), 505 (1996). based on photoassociation data, each on...

Feshbach resonances in ultracold atomic collisions may play an important role in Bose-Einstein condensation. In favorable cases, the resonance energy can be tuned through zero with a magnetic field, and this would allow for tuning of the sign and magnitude of the condensate self-interaction energy. We have searched for such resonances by measuring...

We present results which probe the structure of ${^{85}}Rb_{2}$ very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped ${^{85}}Rb$ atoms. First, we have determined the positions of twelve of the highest vibrational levels of ${^{85}}Rb_{2}$, all...

Using information from a recent Rb-85 two-color photoassociation experiment, we evaluate the merits of fountain clocks based on Rb-87 and Rb-85 isotopes as alternatives to Cs-133, and find that they offer significant advantages; In the case of Rb-87 the collisionally induced fractional frequency shift is 15 times smaller than for Cs-133. This small...

Recent experiments with atomic clocks and hydrogen gas samples have shown discrepancies between theory and experiment. There are serious disagreements with respect to four different parameters: two different frequency shift parameters and a line broadening cross section relating to the H maser, and a longitudinal relaxation rate observed in a hydro...

Ab initio autoionization widths for the Ne(3s)-Ar and Ne(3p)-Ar systems are calculated in a two-electron approximation. Using correctly normalized wave functions, the calculations result in absolute values for the autoionization widths. We use a modified coupled-channel code with ab initio potentials and ionization widths as input to calculate cros...

Intramultiplet mixing collisions have been investigated using polarized Ne(3p) atoms with a well-defined initial relative velocity, i.e., two initial-state vectors. By analyzing the final-state center-of-mass velocity with a (Doppler-detuned) probe laser with a well-defined polarization and detecting the laser-induced fluorescence we measure the di...

We determine the energies of twelve vibrational levels lying within 20GHz of the lowest dissociation limit of ⁸⁵Rbâ with two-color photoassociation spectroscopy of ultracold ⁸⁵Rb atoms. The levels lie in an energy range for which singlet and triplet states are mixed by the hyperfine interaction. We carry out a coupled channels bound state a...

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We use recently measured cold photoassociation and two-photon data to extract the singlet and triplet accumulated radial phases of interacting ground-state lithium atoms. Using the resulting values we predict scattering lengths, Feshbach resonances, and exchange decay rates for cold collisions between 7Li and 6Li atoms that are of interest for the...

We present experimental results of an atomic beam brightener, along with theoretical studies of photoassociation spectroscopy in this beam. The atomic beam of metastable neon atoms is first collimated via transverse Doppler cooling, then Zeeman-slowed along the beam axis, and finally compressed in a 2-D magneto-optical trap. Experimental results fo...

We study the elastic scattering length and inelastic decay rate associated with collisions of 23Na and 87Rb atoms in different hyperfine states: one with atoms in the \|f=2,mf=2> and one with atoms in the \|f=1,mf=-1> state. For Na the real part of the a(22)+(1-1) scattering length for \|22>+\|1-1> collisions is predicted to be positive and equal t...

We observe the time dependence of a cold-atom collision in a pulsed photoassociation experiment. For a g-wave shape resonance in the 85Rb+85Rb system we measure the time needed to build up the resonant state by tunneling through the centrifugal barrier. Combining this with time-independent 85Rb and 87Rb photoassociation we determine the resonance e...

Optical potentials are used in a quantum mechanical treatment of loss processes, e.g., ionization, where the loss of flux is described by the imaginary part. We present a numerical method for calculating two-center two-electron integrals necessary to construct the imaginary part of the optical potential. By introducing Slater-type orbitals with com...

We observe a shape resonance in the scattering of two ultracold 87Rb atoms, causing the colliding atoms to form a long-living compound system inside an l=2 centrifugal barrier. Its existence follows from a photoassociation experiment in a gas sample of doubly polarized 87Rb atoms. Using it we are able to carry out direct determinations of the tripl...

We have determined properties of cold 39K+39K and 41K+41K collisions by a multichannel inverted perturbation approach applied to spectroscopic data of highly excited 39K singlet and triplet bound states. We predict positive scattering lengths for the 39K+39K and 41K+41K singlet potentials, as well as for the 41K+41K triplet potential, and a negativ...

We have determined properties of cold 39 K + 39 K and 41 K + 41 K collisions by a multichannel Inverted Perturbation Approach applied to spectroscopic data of highly-excited 39 K singlet and triplet bound states. We predict positive scattering lengths for the 39 K + 39 K and 41 K + 41 K singlet potentials, as well as for the 41 K + 41 K triplet pot...

In view of two recent Bose-Einstein condensation experiments, we have calculated the magnetic-dipolar decay-rate constants of the atomic density for the doubly polarized state in 87Rb and 85Rb, and for the highest state of the lower hyperfine manifold in 23Na.

We study collisions between dressed ground-state atoms in a full coupled-channel approach. In this way we examine collisions in the microwave trap, in the cryogenic hydrogen maser, and in the context of rf-induced evaporative cooling. The results for dressed H atoms confirm earlier results obtained within the so-called degenerate internal states ap...

Using the knowledge of two-body collision properties that has recently become available, we estimate the three-body recombination rate for doubly spin-polarized ultracold gas samples of 7 Li, 23 Na and 87 Rb on the basis of the Jastrow approximation. We find that only recombination leading to the formation of the highest two-body bound states is im...

In view of recent successful evaporative cooling experiments reaching temperatures in the nK range, we discuss ground-state two-body inelastic and three-body decay rates of dilute cold atomic gas samples at ultralow temperatures. We present theoretical low-temperature two-body decay rates in alkali-atom systems using recently obtained information o...

A technique to cancel the frequency shift due to cold collisions of laser-cooled atoms is proposed. Results for future clocks based on $^{135}\mathrm{Cs}$ and $^{137}\mathrm{Cs}$ are presented. We find a $^{137}\mathrm{Cs}$ fountain clock can be operated with no cold-collision shift by adjusting the population ratios in the fountain, and it may als...

We investigate the resonance properties of ultracold ground state 6Li+6Li, 7Li+7Li, and 23Na+23Na collisions. The locations of various resonances and their corresponding error bounds due to the uncertainty of the interatomic potentials are presented. Also, the resonance widths are computed using rigorous coupled-channel calculations, as well as a m...

Using a multichannel bound-state method we predict the highest bound states of the 23Na diatom system, which are closely related to the collisional behavior of ultracold atoms. The results agree well with a model where the hyperfine interaction is treated in first-order perturbation theory, except for the triplet level closest to the continuum, whi...

We study the collisions of doubly spin-polarized ⁸⁵Rb atoms at millikelvin temperatures using photoassociation spectroscopy. Because the atoms are spin polarized, only triplet collisional states are formed. This leads to photoassociation spectra of a particularly simple form, which provide a very direct probe of the ground state collision. Thes...

We investigate the resonance properties of ultra-cold ground state 6 Li+ 6 Li, 7 Li+ 7 Li and 23 Na+ 23 Na collisions. The locations of various resonances and their corresponding error bounds due to the uncertainty of the inter-atomic potentials are presented. Also the resonance widths are computed using rigorous coupled channels calculations, as w...

This is the first book devoted to Bose–Einstein condensation (BEC) as an interdisciplinary subject, covering atomic and molecular physics, laser physics, low temperature physics and astrophysics. It contains 18 authoritative review articles on experimental and theoretical research in BEC and associated phenomena. Bose–Einstein condensation is a pha...

We present measurements on fine-structure-changing Ne{sup **}{l_brace}(2{ital p})⁵(3{ital p}){r_brace}+He collisions at superthermal energies with an average value of {l_angle}{ital E}{r_angle}=470 meV. For an extensive set of transitions absolute values of polarized-atom cross sections are given. A wide range of cross section magnitudes and pola...

We have determined the scattering length of the ground state 7Li+7Li singlet potential from spectroscopic data on the highest S=0 bound states. Combining this with a previously obtained triplet value we find the first example of an alkali atom hyperfine state (the 7Li F=1, MF=-1 state) for which the scattering length is positive. This implies a sta...

The recent developments in laser cooling, together with a preceding decade of work on cryogenically cooled atomic hydrogen, have opened possibilities for a large variety of experiments in which collisions between very slow atoms play an important role. Examples of such experiments are reviewed with an emphasis on theoretical interpretation. We focu...

We present time-of-flight measurements on fine-structure-changing Ne**{(2p)5(3p)}+He collisions in the energy range 200 less-than-or-equal-to E less-than-or-equal-to 1200 meV. Absolute values of polarized-atom cross sections are given for six collision energies in this range for various transitions from the {alpha5} and {alpha7} initial fine-struct...

Measurements of the electron electric dipole moment have become an important tool in the search for new CP-violating interactions outside the standard model. Some extensions of the standard model predict a value of this moment of the order of the present experimental bound 10⁻²⁶ e{sm_bullet}cm, which underlines the need to improve this bound....

We present a quantum-mechanical study of the dynamics of collisions of cold atoms in a (magneto-) optical trap valid in the linear intensity regime. We find further evidence for a discrepancy with results of the semiclassical optical-Bloch-equation method at lower collision energies and detunings, referred to as ‘‘quantum suppression’’ in previous...

We have improved the theoretical triplet ground-state potential of 7Li2 by means of an inverse perturbation analysis, and find that the diatomic scattering length for 7Li atoms in the F=2, mF=2 ground-state hyperfine level is negative. The consequences of this result for achieving Bose-Einstein condensation in a trapped ultracold 7Li gas sample are...

We interpret recently measured collisional frequency shifts in a cesium atomic fountain using coupled-channel theory and a simple picture of hyperfine-coupled long-range molecular states. We predict the existence of Cs2 singlet and triplet states very close to threshold with an associated strong influence on ultracold collisions and large negative...

We describe a hydrogen maser operating at very low temperatures in which most of the hydrogen atoms are condensed on a superfluid helium surface in long-lived states. This proposed maser can be used to obtain information on the properties of the hydrogen–liquid-helium-surface system. In addition, it promises to be an interesting system from the poi...

We present a coupled-channel study of optical collisions, restricted to a single atom-laser manifold. Outside of a resonance region around the Condon point, we find a simple representation of the solution in terms of propagating complex dressed states. The probability flux for the 2P3/2+S state at small interatomic distances can be interpreted in t...

We study the magnetic-field dependence of the cross sections for elastic and inelastic collisions of pairs of ultracold cesium atoms in a magnetic trap, calculated with the coupled-channels method. We pay special attention to atoms in the f=3, mf=-3 weak-field seeking state of the lower hyperfine manifold. The cross sections show a pronounced reson...

We study the spin-exchange frequency shifts and line broadening of the deuterium maser in the temperature range from 0 to 10 K. We consider both a version operating on the β-ε transition at B=3.0 μT and one operating on the β-δ transition at B=3.9 mT. For the first transition, a comparison is made with our earlier results based on the degenerate-in...

We study conditions necessary for the observation of Bose-Einstein condensation in a magnetically trapped sample of atomic Cs gas. These conditions are associated with the value of the elastic scattering length, the rate of elastic scattering events, and the lifetime for decay of the density due to both magnetic dipole relaxation in two-body collis...

In connection with experiments aiming at the improvement of the cesium atomic beam clock by means of a fountain of laser-cooled cesium atoms, we present expressions for the line shift and line broadening due to collisions between cesium atoms. The coherent collision cross sections occurring in these expressions are calculated by means of the couple...

For the molecular targets CH4, H2, N2, O2, CO, CO2 and N2O we have investigated the ionization cross section 3Q for collisions with laser excited Ne**{(2p)5(3p); J = 3} atoms in the range 100 ⩽ E ⩽ 4000 meV of collision energies (80 ⩽ E ⩽ 800 meV for H2). A crossed-beam apparatus with well defined beam geometry is used, which allows the investigati...

Following Jones and Dahler [Phys. Rev. A 37, 2916 (1988)] we study the theory of the process of ionization within the framework of the Feshbach projection-operator formalism, with the discrete fine-structure states (before ionization) and the continuum states (after ionization) as the two separate subspaces of Hilbert space. For the Ne*(3s)-Ar and...

We examine the dynamical behavior of the cryogenic hydrogen maser. Studying the coupled field-matter equations, which have been reduced to the complex Lorenz equations, we obtain two operating domains, one in which steady-state oscillation takes place and a time-dependent domain that is characterized by a pulsed output power. For the latter we obta...

We study hyperfine transitions in collisions between cold ground-state 23Na atoms, which are of crucial importance for the decay of the atomic density in magnetic traps. For comparable densities we find the initial decay by exchange collisions to be roughly a factor of 10 more rapid than that in atomic hydrogen. The doubly polarized atomic gas that...

Following Jones and Dahler (Phys. Rev. A 37, 2916 (1988)) we study the theory of the process of ionization within the framework of the Feshbach projection-operator formalism, with the discrete fine-structure states (before ionization) and the continuum states (after ionization) as the two separate subspaces of Hilbert space. For the Ne{sup *}(3{ita...

A compact device (lengh 175 mm) has been built for the energy resolved detection of low energy (1-5 eV) Penning electrons with a 2π solid angle collection efficiency, based on the principle of adiabatic parallelisation of electron motion in a diverging magnetic field. A retarding field analysis is then used as a high pass filter to discriminate bet...

In a crossed-beam experiment the total ionization cross section for the title systems has been investigated in the range 0.1. The observed polarization effect at E=0.1 eV is Q3\|M\|=0,1/Q3\|M\|=3=2.5, which is in good agreement with the data of Bussert, T. Bregel, R. J. Allan, M. W. Ruf, and H. Hotop [Z. Phys. A 320, 105 (1985)] in the thermal ener...

We derive expressions for the spin-exchange frequency shift and line broadening of the deuterium maser for low temperatures and present the results of a preliminary calculation based on the Degenerate-Internal-States approximation and its first-order correction.

The Degenerate-Internal-States approximation as well as its first-order correction are shown to provide a convenient method for calculating elastic and inelastic collision amplitudes for low temperature atomic scattering.

We show that the Maxwell-Bloch equations, describing the dynamics of the sub-Kelvin H maser, predict unstable and chaotic oscillations in a regime which should be easily accessible experimentally.

It is pointed out that the usual oscillation condition of the H maser is only a necessary condition for steady operation. Reducing the coupled field-matter dynamics to the complex Lorenz equations we derive a second requirement which together with the first forms a set of necessary and sufficient conditions for the steady operation to be stable. Th...

We propose a new method for studying the reflection of a hydrogen atom from a superfluid-helium film. Starting from the narrow width of the reflected angular distribution recently found experimentally, we tentatively extrapolate to the extreme limit of low ripplon wave numbers in which the adiabatic or degenerate-internal-states approximation becom...

DOI:https://doi.org/10.1103/PhysRevLett.64.2106

We study the spin-exchange frequency shift of the cryogenic hydrogen maser for B≠0. A general expression is derived in terms of populations of ground-state hyperfine levels. The coefficients in this expression are calculated in the degenerate-internal-states approximation, as well as to first order in the hyperfine plus Zeeman splitting. Numerical...

In a crossed-beam experiment the total ionization cross section for the title systems has been investigated in the range 0.1â¤{ital E} (eV) >=4 of collision energies. The population of the short-lived Ne{sup **}((3{ital p});{ital J}=3) state is produced by saturated optical pumping of the Ne{sup *}((3{ital s});{ital J}=2)âNe{sup **}((3{ital p});{it...

The room-temperature hydrogen maser ¹ is the most stable existing frequency standard for a wide range of measuring times. As such it has been used very successfully for tests of general relativity, for Very Long Baseline Interferometry (VLBI) and for interplanetary navigation (Voyager mission). Since some years work is going on to build a sub-Kelvi...

We present a calculation of the effective rate constant for three-body recombination, taking rearrangement into account. We find a pronounced resonance structure as a function of magnetic field due to long-range rovibrational states of H3 in an almost equilateral configuration. This structure is superposed on a rather flat background with a slow de...

We discuss a resonant microwave trap for neutral atoms. Because of the long spontaneous radiation time this trap is remarkably different from the optical trap. It also has advantage over static magnetic traps that trap the excited spin state of the lowest electronic level, in that atoms predominantly in the spin ground state can be trapped. We anal...