No abstract

New photoassociation data on the 0 + u levels of Rb 2 below the 5S+5P 1/2 limit are combined with older data (Cline et al 1994 Phys. Rev. Lett. 73 632) in a fit to potentials and spin-orbit functions. The P 1/2 data exhibit oscillations in the B(v) values due to coupling between the two 0 + u series, as modelled accurately by a coupled potentials approach. The fitted value for the C 3 dispersion parameter from the combined data agrees well with the value derived from the pure long-range 0 − g state.

We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 23 Na atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field.Although Bose-Einstein condensates (BECs) are often thought of for sensitive measurements, their spatial coherence is not always necessary. Thermal atomic collisions are often mistakenly thought to be incoherent but, while keeping track of the spatial coherence is difficult, coherence can sometimes more easily be followed in the internal degrees of freedom. Thus, cold thermal clouds are often just as sensitive for use in spin measurements. In this work, we demonstrate collisionally-driven coherent spin population oscillations that can be interpreted as zero-momentum spin waves in a cold thermal cloud of spin-1 atoms. Such oscillations were previously only seen in the context of BECs [1-5] and two-atom, singlespatial-mode systems [6,7]. The spin oscillations that we observe in a highly multi-spatial-mode thermal gas are remarkable in that they can be described by a theory that is independent of the spatial degrees of freedom.Well-known examples of thermal spin systems that preserve internal spin states include optically-pumped dilute gases used for magnetometry [8] and spin-polarized noble gas imaging [9]. The spin polarization can be maintained even while the gas is trapped in glass cells, or by living tissues like lungs. Hydrogen masers are based on interrogating the free precession of a spin superposition of a thermal gas in a glass cell. Less well-known, collisionally-driven spin-wave effects were predicted in 1982 [10,11], and observations of such effects were reported soon thereafter in low-temperature spin-polarized hydrogen [12]. Bosonic and fermionic alkali pseudo-spin-1/2 systems have also been studied [13][14][15], and spin domain formation has been observed in these systems [16][17][18]. Due to the spindependent interaction that is absent in the pseudo-spin-1/2 system, a spin-1 gas is predicted to have additional interesting coherent collisional (spinor) dynamics which give rise to spin waves or population oscillations [19,20].The dynamics of spinor BECs have been widely investigated in spin-1 Na and Rb gases, as reviewed in Refs. [21,22]. Rb in the F = 1 state is ferromagnetic (spin-aligned collisions having the lowest energy), whereas Na is considered antiferromagnetic. Both o...

We have studied the effect of resonant electronic state coupling on the formation of ultracold ground-state 85 Rb2. Ultracold Rb2 molecules are formed by photoassociation (PA) to a coupled pair of 0 + u states, 0 + u (P 1/2 ) and 0 + u (P 3/2 ), in the region below the 5S + 5P 1/2 limit. Subsequent radiative decay produces high vibrational levels of the ground state, X 1 Σ + g . The population distribution of these X state vibrational levels is monitored by resonance-enhanced two-photon ionization through the 2 1 Σ + u state. We find that the populations of vibrational levels v ′′ =112−116 are far larger than can be accounted for by the Franck-Condon factors for 0 + u (P 1/2 ) → X 1 Σ + g transitions with the 0 + u (P 1/2 ) state treated as a single channel. Further, the ground-state molecule population exhibits oscillatory behavior as the PA laser is tuned through a succession of 0 + u state vibrational levels. Both of these effects are explained by a new calculation of transition amplitudes that includes the resonant character of the spin-orbit coupling of the two 0 + u states. The resulting enhancement of more deeply bound ground-state molecule formation will be useful for future experiments on ultracold molecules. PACS numbers: 32.80.Pj, 32.80.Qk, 34.50.Rk. 0 5 10 15 20 0 10 20 30 40 SE b 3 u R(Å) Energy (10 3 cm -1 ) Rb + 2 5S + 4D 5S + 5P 5S + 5S X 1 + g A 1 + u 2 1 + u 2 + g PÃ 600nm FIG. 1: (color online) Selected potential curves for Rb2 from Ref. [14], showing our scheme for forming ultracold 85 Rb2 molecules in the X 1 Σ + g state. Photoassociation (PA) is used to excite high-v levels of the coupled 0 + u states, 0 + u (P 1/2 ) and 0 + u (P 3/2 ), converging to the 5S + 5P 1/2 and 5S + 5P 3/2 atomic limits. These states correlate at short range to the A 1 Σ + u and b 3 Πu states. Spontaneous emission (SE) from these levels populates the ground X state. Pulsed laser light at 600 nm is used for ionization detection.