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Imidogen (NH) radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational and rotational ground state imidogen in collisions with 3 He is measured to be 3.8 ± 1.1 × 10 −19 cm 2 at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of γ = 7 × 10 4 , in agreement with recent theory [1].

We present an experimental and theoretical study of atom-molecule collisions in a mixture of cold, trapped N atoms and NH molecules at a temperature of ∼600  mK. We measure a small N+NH trap loss rate coefficient of k(loss)(N+NH)=9(5)(3)×10(-13)  cm(3) s(-1). Accurate quantum scattering calculations based on ab initio interaction potentials are in agreement with experiment and indicate the magnetic dipole interaction to be the dominant loss mechanism. Our theory further indicates the ratio of N+NH elastic-to-inelastic collisions remains large (>100) into the mK regime.

We realized a quantum geometric “charge” pump for a Bose-Einstein condensate (BEC) in the lowest Bloch band of a novel bipartite magnetic lattice. Topological charge pumps in filled bands yield quantized pumping set by the global – topological – properties of the bands. In contrast, our geometric charge pump for a BEC occupying just a single crystal momentum state exibits non-quantized charge pumping set by local – geometrical – properties of the band structure. Like topological charge pumps, for each pump cycle we observed an overall displacement (here, not quantized) and a temporal modulation of the atomic wavepacket’s position in each unit cell, i.e., the polarization.

Employing a two-stage cryogenic buffer gas cell, we produce a cold, hydrodynamically extracted beam of calcium monohydride molecules with a near effusive velocity distribution. Beam dynamics, thermalization and slowing are studied using laser spectroscopy. The key to this hybrid, effusive-like beam source is a "slowing cell" placed immediately after a hydrodynamic, cryogenic source [Patterson et al., J. Chem. Phys., 2007, 126, 154307]. The resulting CaH beams are created in two regimes. One modestly boosted beam has a forward velocity of v f = 65 m/s, a narrow velocity spread, and a flux of 10 9 molecules per pulse. The other has the slowest forward velocity of v f = 40 m/s, a longitudinal temperature of 3.6 K, and a flux of 5 × 10 8 molecules per pulse.

We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold 3 Σ molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in collisions with 3 He and 4 He. The 4 He data support the predicted 1/B 2 e dependence of the collisioninduced Zeeman relaxation rate coefficient on the molecular rotational constant B e . The measured 3 He rate coefficients are much larger than 4 He and depend less strongly on B e , and the theoretical analysis indicates they are strongly affected by a shape resonance. The results demonstrate the influence of molecular structure on collisional energy transfer at low temperatures.

The v = 1 → 0 radiative lifetime of NH (X 3 Σ − , v = 1, N = 0) is determined to be τ rad,exp. = 37.0±0.5 stat +2.0 −0.8 sys ms, corresponding to a transition dipole moment of |µ 10 | = 0.0540 +0.0009 −0.0018 D. To achieve the long observation times necessary for direct time-domain measurement, vibrationally excited NH (X 3 Σ − , v = 1, N = 0) radicals are magnetically trapped using helium buffer-gas loading. Simultaneous trapping and lifetime measurement of both the NH(v = 1, N = 0) and NH(v = 0, N = 0) populations allows for accurate extraction of τ rad,exp. . Background helium atoms are present during our measurement of τ rad,exp. , and the rate constant for helium atom induced collisional quenching of NH(v = 1, N = 0) was determined to be k v=1 < 3.9 × 10 −15 cm 3 s −1 . This bound on k v=1 yields the quoted systematic uncertainty on τ rad,exp. . Using an ab initio dipole moment function and an RKR potential, we also determine a theoretical value of 36.99 ms, in agreement with our experimental value. Our results provide an independent determination of τ rad ,10 , test molecular theory, and furthermore demonstrate the efficacy of buffer-gas loading and trapping in determining metastable radiative and collisional lifetimes.

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