We describe the operation of a laser cooled cesium fountain clock in the quantum limited regime. An ultrastable cryogenic sapphire oscillator is used to measure the short-term frequency stability of the fountain as a function of the number of detected atoms $N_{\mathrm{at}}$. For $N_{\mathrm{at}}$ varying from $4\times {10}^4$ to $6\times {10}^5$ the Allan standard deviation of the frequency fluctuations is in excellent agreement with the $N_{\mathrm{at}}^{-1/2\mathrm{}}$ law of atomic projection noise. With $6\times {10}^5$ atoms, the relative frequency stability is $4\times {10}^{-14\mathrm{}}{\tau }^{-1/2\mathrm{}}$, where τ is the integration time in seconds. This is the best short-term stability ever reported for primary frequency standards, a factor of 5 improvement over previous results.

We demonstrate an ultrastable ${\mathrm{CO}}_2$ laser trap that provides tight confinement of neutral atoms with negligible optical scattering and minimal laser-noise-induced heating. Using this method, fermionic ${}^6\mathrm{Li}$ atoms are stored in a 0.4 mK deep well with a $1/e$ trap lifetime of 300 sec, consistent with a background pressure of ${10}^{-11\mathrm{}}\mathrm{Torr}$. To our knowledge, this is the longest storage time ever achieved with an all-optical trap, comparable to the best reported magnetic traps.

Strong infrared fields can be used for controlled spinning of molecules to very high angular momentum states. The angular momentum acquired can be sufficient to break molecular bonds. The approach is suitable for all anisotropic molecules, and we illustrate it by dissociating a homonuclear diatomic ${\mathrm{Cl}}_2$, with optical centrifuge efficiently separating ${\mathrm{Cl}}^{35}$ and ${\mathrm{Cl}}^{37}$ isotopes and thus demonstrating high sensitivity to the moment of inertia.

A fourth-order Young interference experiment was done to demonstrate a practical way to measure the de Broglie wavelength of a two-photon wave packet. A two-photon collinear beam is generated by type-II spontaneous parametric down-conversion. By modifying the transverse field profile of the pump laser beam that generates the two-photon beam we demonstrate that it is possible to measure the de Broglie wavelength of the single-photon constituents of the two-photon wave packet, the de Broglie wavelength of the two-photon wave packet as a whole and an ill defined intermediate de Broglie wavelength between the two cases.

We demonstrate a juggling atomic fountain by launching two laser-cooled balls of ${}^{133}\mathrm{Cs}$ atoms in rapid succession. The atoms collide near the top of the fountain and, by varying the delay between launches, we scan the collision energy from 19 to $150\mu \mathrm{K}$. We measure the differential scattering cross section and isolate the contributions from different partial waves including their interferences. We observe the $s$-wave energy dependence and the $p$-wave scattering threshold. We infer a triplet $s$-wave scattering length of ${-400a}_0$ and a $p$ wave of $({-107a}_0{)}^3$ for $|F=4,m=4\mathrm{}〉+|3,3〉$.

Through use of quantum coherence in an atomic system, we demonstrate that an optical field can be used to completely control the polarization state of another field. Theoretical and experimental results show that by applying a field with a frequency tuned near one transition, an initially isotropic atomic vapor can be made to behave as a linearly or circularly birefringent material for fields tuned near an adjoining transition.

We observe the effects of noise and dissipation on dynamical localization. Our system consists of cold cesium atoms in a pulsed standing wave of light, and is an experimental realization of the $\delta$-kicked rotor. We compare the effects of amplitude noise with those of spontaneous scattering. The experimental signature in both cases is an increased growth in energy, with qualitatively similar momentum distributions.

We have studied the temporal coherence of high-order harmonics (up to the 15th order) produced by focusing 100 fs laser pulses into an argon gas jet. We measure the visibility of the interference fringes, produced when two spatially separated harmonic sources interfere in the far field, as a function of the time delay between the two sources. In general, we find long coherence times, comparable to the expected pulse durations of the harmonics. For some of the harmonics, the interference pattern exhibits two regions, with significantly different coherence times. These results are interpreted in terms of different electronic trajectories contributing to harmonic generation.

We have completely determined the amplitude and phase of a quantum wave packet. The wave packet was shaped using a programmable optical pulse. Phase information comes from analysis of covariant fluctuations due to interference between the wave packet and a well-characterized reference.

The combination of cold atoms and large coherent coupling enables investigations in a new regime in cavity QED with single-atom trajectories monitored in real time with high signal-to-noise ratio. The underlying “vacuum-Rabi” splitting is clearly reflected in the frequency dependence of atomic transit signals recorded atom by atom, with evidence for mechanical light forces for intracavity photon number $<1\mathrm{}$. The nonlinear optical response of one atom in a cavity is observed to be in accord with the one-atom quantum theory but at variance with semiclassical predictions.

A mesoscopic superposition of quantum states involving radiation fields with classically distinct phases was created and its progressive decoherence observed. The experiment involved Rydberg atoms interacting one at a time with a few photon coherent field trapped in a high $Q$ microwave cavity. The mesoscopic superposition was the equivalent of an “ $\mathrm{atom}+\mathrm{measuring}\mathrm{apparatus}$” system in which the “meter” was pointing simultaneously towards two different directions—a “Schrödinger cat.” The decoherence phenomenon transforming this superposition into a statistical mixture was observed while it unfolded, providing a direct insight into a process at the heart of quantum measurement.

We demonstrate that high-order harmonics generated by an atom in intense laser field form trains of ultrashort pulses corresponding to different trajectories of electrons that tunnel out of the atom and recombine. Propagation in an atomic jet allows us to select one of these trajectories, leading to a train of pulses of extremely short duration.