We observe coherent spin oscillations in an antiferromagnetic spin-1 Bose-Einstein condensate of sodium. The variation of the spin oscillations with magnetic field shows a clear signature of nonlinearity, in agreement with theory, which also predicts anharmonic oscillations near a critical magnetic field. Measurements of the magnetic phase diagram agree with predictions made in the approximation of a single spatial mode. The oscillation period yields the best measurement to date of the sodium spin-dependent interaction coefficient, determining that the difference between the sodium spin-dependent s-wave scattering lengths a f =2 −a f =0 is 2.47 ± 0.27 Bohr radii. [3,4] in which the population oscillates between different Zeeman sublevels. We present the first observation of coherent spin oscillations in a spin-1 condensate with antiferromagnetic interactions (in which the interaction energy of colliding spin-aligned atoms is higher than that of spin-antialigned atoms.)Spinor condensates have been a fertile area for theoretical studies of dynamics [5,6,7,8] At low magnetic fields, spin interactions dominate the dynamics. The different sign of the spin dependent interaction causes the antiferromagnetic F=1 case to differ from the ferromagnetic one both in the structure of the ground-state magnetic phase diagram and in the spinor dynamics. Both cases can exhibit a regime of slow, anharmonic spin oscillations; however, this behavior is predicted over a wide range of initial conditions only in the antiferromagnetic case [8]. The spin interaction energies in sodium are more than an order of magnitude larger than in 87 Rb F = 1 for a given condensate density [3], facilitating studies of spinor dynamics.The dynamics of the spin-1 system are much simpler than the spin-2 case [4,15,16], having a well-developed analytic solution [8]. This solution predicts a divergence in the oscillation period (not to be confused with the amplitude peak observed in 87 Rb F=2 [4] oscillations).This Letter reports the first measurement of the ground state magnetic phase diagram of a spinor condensate, and the first experimental study of coherent spinor dynamics in an antiferromagnetic spin-1 condensate. Both show good agreement with the single-spatialmode theory [10]. To study the dynamics, we displace the spinor from its ground state, observing the resulting oscillations of the Zeeman populations as a function of applied magnetic field B. At low field the oscillation period is constant, at high field it decreases rapidly, and at a critical field it displays a resonance-like feature, all as predicted by theory [8]. These measurements have allowed us to improve by a factor of three the determination of the sodium F = 1 spin-dependent interaction strength, which is proportional to the difference a f =2 − a f =0 in the spin-dependent scattering lengths.The state of the condensate in the single-mode approximation (SMA) is written as the product φ(r)ζ of a spin-independent spatial wavefunction φ(r) and a spinor ζ = ( √ ρ − e iθ− , √ ρ 0 e iθ0 ,...

We use time-correlated single-photon counting techniques on a sample of 210 Fr atoms confined and cooled in a magneto-optical trap to measure the lifetimes of the 9S 1/2 , 8P 3/2 , and 8P 1/2 excited levels. We populate the 9S 1/2 level by two-photon resonant excitation through the 7P 1/2 level. The direct measurement of the 9S 1/2 decay through the 7P 3/2 level at 851 nm gives a lifetime of 107.53± 0.90 ns. We observe the decay of the 9S 1/2 level through the 8P 3/2 level at 423 nm and the 8P 1/2 level at 433 nm down to the 7S 1/2 ground level, and indirectly determine the lifetimes of these to be 83.5± 1.5 ns and 149.3± 3.5 ns, respectively.

Francium is a candidate for atomic parity non-conservation (PNC) experiments. Its simple atomic structure has been the subject of extensive experimental research facilitated by the ability to trap and cool significant numbers of atoms. The studies include the location of energy levels, their hyperfine splittings and their lifetime. All of these levels are close to the ground state. The results show a remarkable agreement with calculated ab initio properties to a degree that is comparable with other stable alkali atoms. The quantitative understanding of francium has made possible the exploration of avenues for a PNC measurement in the optical and the microwave regimes. These precision experiments have the potential to enhance our understanding of the weak coupling constants between electrons and nucleons, as well as between nucleons.