The 7.8 eV nuclear isomer transition in 229 thorium has been suggested as a clock transition in a new type of optical frequency standard. Here we discuss the construction of a 'solid-state nuclear clock' from thorium nuclei implanted into single crystals transparent in the vacuum ultraviolet range. We investigate crystal-induced line shifts and broadening effects for the specific system of calcium fluoride. At liquid nitrogen temperatures, the clock performance will be limited by decoherence due to magnetic coupling of the thorium nuclei to neighboring nuclear moments, ruling out the commonly used Rabi or Ramsey interrogation schemes. We propose clock stabilization based on a fluorescence spectroscopy method and present optimized operation parameters. Taking advantage of the large number of quantum oscillators under continuous interrogation, a fractional instability level of 10 −19 might be reached within the solid-state approach.

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We demonstrate and analyze a novel scheme for complete transfer of atomic or molecular population between two bound states, by means of Stark-chirped rapid adiabatic passage ͑SCRAP͒. In this two-laser technique a delayed-pulse laser-induced Stark shift sweeps the transition frequency between two coupled states twice through resonance with the frequency of the population-transferring coupling laser. The delay of the Stark-shifting pulse with respect to the pulse of the coupling-laser Rabi frequency guarantees adiabatic passage of population at one of the two resonances while the evolution is diabatic at the other. The SCRAP method can give a population-transfer efficiency approaching unity. We discuss the general requirements on the intensity and timing of the pulses that produce the Rabi frequency and, independently, the Stark shift. We particularly stress extension to a double-SCRAP technique, a coherent variant of stimulated emission pumping in the limit of strong saturation. We demonstrate the success of the SCRAP method with experiments in metastable helium, where a two-photon transition provides the Rabi frequency.

We propose the use of Stark chirped rapid-adiabatic-passage method, a technique in which the energy of a target state is swept through resonance by a slowly varying dynamic Stark shift to induce complete population transfer from the ground 1s state to the metastable 2s state of the hydrogen atom. Parasitic ionization processes are strongly reduced by using a two-color excitation scheme. Our detailed numerical calculations show that under judicious choice of pulse parameters, up to 98% of the population can be found in the 2s state at the end of the process. ͓S1050-2947͑99͒51112-8͔ PACS number͑s͒: 42.50.Md FIG. 4. Calculated two-photon line shapes for three values of uv-pulse fluence: 50 J/cm 2 ͑1͒, 100 J/cm 2 ͑2͒, and 150 J/cm 2 ͑3͒.The vuv-pulse fluence is 0.01 J/cm 2 and the IR ͑Stark͒ pulse fluence is 1 J/cm 2 . The Stark pulse duration is T S ϭ1.5T p and the time delay is ϭ1.2T p . RAPID COMMUNICATIONS R4240PRA 60 YATSENKO, SHORE, HALFMANN, BERGMANN, AND VARDI