Atom--Molecule Coherence in a Bose-Einstein Condensate

Coherent coupling between atoms and molecules in a Bose-Einstein condensate (BEC) has been observed. Oscillations between atomic and molecular states were excited by sudden changes in the magnetic field near a Feshbach resonance and persisted for many periods of the oscillation. The oscillation frequency was measured over a large range of magnetic fields and is in excellent quantitative agreement with the energy difference between the colliding atom threshold energy and the energy of the bound molecular state. This agreement indicates that we have created a quantum superposition of atoms and diatomic molecules, which are chemically different species.Comment: 7 pages, 6 figure

Rapid sympathetic cooling to Fermi degeneracy on a chip

Neutral fermions present new opportunities for testing many-body condensed matter systems, realizing precision atom interferometry, producing ultra-cold molecules, and investigating fundamental forces. However, since their first observation, quantum degenerate Fermi gases (DFGs) have continued to be challenging to produce, and have been realized in only a handful of laboratories. In this Letter, we report the production of a DFG using a simple apparatus based on a microfabricated magnetic trap. Similar approaches applied to Bose-Einstein Condensation (BEC) of 87Rb have accelerated evaporative cooling and eliminated the need for multiple vacuum chambers. We demonstrate sympathetic cooling for the first time in a microtrap, and cool 40K to Fermi degeneracy in just six seconds -- faster than has been possible in conventional magnetic traps. To understand our sympathetic cooling trajectory, we measure the temperature dependence of the 40K-87Rb cross-section and observe its Ramsauer-Townsend reduction.Comment: 5 pages, 4 figures (v3: new collision data, improved atom number calibration, revised text, improved figures.

Coherent spinor dynamics in a spin-1 Bose condensate

Collisions in a thermal gas are perceived as random or incoherent as a consequence of the large numbers of initial and final quantum states accessible to the system. In a quantum gas, e.g. a Bose-Einstein condensate or a degenerate Fermi gas, the phase space accessible to low energy collisions is so restricted that collisions be-come coherent and reversible. Here, we report the observation of coherent spin-changing collisions in a gas of spin-1 bosons. Starting with condensates occupying two spin states, a condensate in the third spin state is coherently and reversibly created by atomic collisions. The observed dynamics are analogous to Josephson oscillations in weakly connected superconductors and represent a type of matter-wave four-wave mixing. The spin-dependent scattering length is determined from these oscillations to be -1.45(18) Bohr. Finally, we demonstrate coherent control of the evolution of the system by applying differential phase shifts to the spin states using magnetic fields.Comment: 19 pages, 3 figure

Observation of electric quadrupole transitions to Rydberg nd states of ultracold rubidium atoms

We report the observation of dipole-forbidden, but quadrupole-allowed, one-photon transitions to high-Rydberg states in Rb. Using pulsed uv excitation of ultracold atoms in a magneto-optical trap, we excite 5s¿nd transitions over a range of principal quantum numbers n=27–59. Compared to dipole-allowed (E1) transitions from 5s¿np, these E2 transitions are weaker by a factor of approximately 2000. We also report measurements of the anomalous np3/2:np1/2 fine-structure transition strength ratio for n=28–75. Both results are in agreement with theoretical predictions

Radio-frequency spectroscopy of ultracold fermions

10.1126/science.1085335SCIENCE30056261723-172