We have produced a very cold sample of spin-polarized trapped atoms. The technique used dramatically simplifies the production of laser-cooled atoms. In this experiment, 1.8x10' neutral cesium atoms were optically captured directly from a low-pressure vapor in a small glass cell. We then cooled the & 1-mm' cloud of trapped atoms and loaded it into a low-field magnetic trap in the same cell. The magnetically trapped atoms had an eAective temperature as low as 1.1+ 0.2 pK, which is the lowest kinetic temperature ever observed and far colder than any previous sample of trapped atoms. Such an optically trapped sample is useful for many applications, but it has some inherent limitations; the atomic spins are randomly oriented, perturbing light fields must be present, and it is di%cult to achieve temperatures lower than 300 pK. We have overcome these limitations by loading the optically trapped atoms into a magnetostatic trap. Because the atoms are very cold when first loaded, we can trap them with relatively small magnetic fields. By properly cooling the atoms before turning on the magnetic trap we have produced a sample which is more than 100 times colder than any previously trapped neutral atoms.In where the steady-state number N, is given by N, =Rr =(1/J6)(V . /o')v, (m/2kT) .

this has the value 8xl0" 13 . Clearly a compensating shift would occur for absorption provided source and absorber were identical and at the same temperature. A small difference in temperature between source and absorber leads to a relative shift per degree given by 6E/E =Cp/2c 2 where Cp is the specific heat. For Fe at 300°K this is 2.2xlO" 15 /°K. This is sufficient for it to be necessary to take it into account in accurate experiments using the resonance absorption of Mach's principle states that the inertial mass of a body is determined by the total distribution of matter in the universe; if the matter distribution is not isotropic, it is conceivable that the mass of a body depends on its direction of acceleration and is a tensor rather than a scalar quantity. Thus the matter in our galaxy is not distributed isotropically with respect to the earth, and hence the mass of a body on the earth may depend on the direction of its acceleration with respect to the direction towards the center of our galaxy. Cocconi and Salpeter 1 have proposed that the total inertial mass of a body on the earth be considered the sum of an isotropic part m and an anisotropic part Am, and that the contribution to the mass of a body on the earth due to a mass 9TC a distance r away from the body is proportional to < M/r p (0 ^ v ^ 1). The ratio of Am, due to a mass sn a distance r away, to m, due to the total mass in the universe, isin which p = average density of matter in the universe (10" 29 g/cm 3 ) and R = radius of the universe (3xl0 27 cm). 2 If Am is ascribed to our own galaxy, thenr = 2.5xl0 22 cm and 3Tl=3xl0 44 g, where the total mass of the galaxy is considered concentrated at its center. Hence for v-1, Am/m=2xl0" 5 and for ^ = 0, Am/m=3xl0" 10 . Cocconi and Salpeter have suggested several experiments to test for this anisotropy of mass based on the observation that the contribution to the binding energy of a particle in a Coulomb y rays, such as those to measure the gravitational red shift. 2 ' 3 I would like to thank Dr. Ziman, Professor O. R. Frisch, and Dr. W. Marshall for helpful discussions. 1 R. L. Mossbauer, Z. Physik 151, 124(1958). 2 R. V. Pound and G. A. Rebka, Phys. Rev. Letters 3, 554 (1959). 3 T. E. Cranshaw, J. P. Schiffer, and A. B. Whitehead, Phys*. Rev. Letters 4, 163(1960).potential due to the anisotropic mass term Am is AE = (Am/m)TP 2 (cos0).(2)Here T is the average kinetic energy of the particle, P 2 is the Legendre polynomial of order 2, and 9 is the angle between the direction of acceleration of the particle (determined by the direction of an external magnetic field H and by the magnetic quantum state) and the direction to the galactic center. This equation is based on the assumption that Am varies as P 2 (cos0). The first experiment suggested was to observe the Zeeman splitting in an atom 1 and the second was to observe the Zeeman splitting in the excited nuclear state of Fe 57 by use of the Mossbauer effect. 3 [The change in binding energy due to Am will not be given exactly by Eq.(2) in the nuclear ...

Laser oscillation without population inversion is demonstrated experimentally in a V-type atomic configuration within the D 1 and D 2 lines of Rb vapor. It is shown that the effect is due to the atomic interference. The experimental results, as first predicted by careful theoretical analysis, are in a good agreement with detailed calculations.