Population dynamics in weakly-excited clouds of ultracold 87 Rb Rydberg atoms were studied by means of trap loss, fluorescence detection, and state dependent stimulated emission. Rydberg atoms were excited to various nl Rydberg states via continuous two-photon excitation from a magnetooptical trap. A stimulated emission probe laser was then used to bring the Rydberg atoms down to the 6P 3/2 state, allowing state-dependent detection of the Rydberg atoms. Measurements of trap loss and fluorescent emission reveal information about the evolution of the Rydberg populations. In particular, population in the initial Rydberg state quickly transfers to other Rydberg states by a non-collisional mechanism, likely superradiant emission. The trap-loss measurements are consistent with black-body ionization as the dominant loss mechanism.

Four-wave mixing can be used to generate coherent output beams, with frequencies difficult to acquire in commercial lasers. Here, a single narrow external cavity diode laser locked to the two photon 5s-5d transition in rubidium is combined with a tapered amplifier system to produce a high power cw beam at 778 nm and used to generate coherent light at 420 nm through parametric four-wave mixing. This process is analyzed in terms of the intensity and frequency of the incoming beam as well as the atomic density of the sample. The efficiency of the process is currently limited when on resonance due to the absorption of the 420 nm beam, and modifications should allow a significant increase in output power.

Ultracold Rb atoms were used to demonstrate nondegenerate four-wave mixing through a Rydberg state. Continuous 5S-5P-nD two-photon excitation to the Rydberg state was combined with an nD-6P tuned laser in a phase-matched geometry. The angular dependence, spatial profile, and dependence on detuning were investigated, showing good agreement with theory. Under optimum conditions 50% of the radiation was emitted into the phase-matched direction. The directional emission is promising for studying quantum effects in blockaded atom clouds.

We demonstrate the production of micron-sized high density atom clouds of interest for mesoscopic quantum information processing. We evaporate atoms from 60 µK, 3 × 10 14 atoms/cm 3 samples contained in a highly anisotropic optical lattice formed by interfering diffracted beams from a holographic phase plate. After evaporating to 1 µK by lowering the confining potential, in less than a second the atom density reduces to 8×10 13 cm −3 at a phase space density approaching unity. Adiabatic recompression of the atoms then increases the density to levels in excess of 1 × 10 15 cm −3 . The resulting clouds are typically 8 µm in the longest dimension. Such samples are small enough to enable mesoscopic quantum manipulation using Rydberg blockade and have the high densities required to investigate new collision phenomena.

We have investigated the frequency characteristics of the coherent 420 nm beam generated via parametric four-wave mixing (FWM). A single, high-power 778 nm laser is directed through a high-density rubidium cell with a detuning of 1 THz from the intermediate state, generating fields at 420 nm and 5.23 μm through FWM. The frequency of the 420 nm light has been found to shift as the excitation laser is tuned. The measured frequency shift ratio of 1.87±0.04 corresponds with the selection of a different velocity class at each excitation frequency, implying that the 5.23 μm beam frequency is correspondingly shifted. The 420 nm light has been tuned over a range of 1 GHz. This parametric FWM process has potential application as a tunable photon source at novel wavelengths.