Double ionization of helium by electron impact is studied in a kinematical complete experiment in the threshold regime at 5 eV excess energy. As expected the recoil ion carries the full initial projectile momentum and the emitted electrons’ sum momentum in average is zero. The electron emission is revealed to be completely dominated by the symmetric 120° configuration predicted by many threshold theories but never observed experimentally before. Fully differential cross sections show a more complex structure than expected for a pure threshold collision dynamics.

We demonstrate spin squeezing in a room temperature ensemble of $\approx {10}^{12}$ cesium atoms using their internal structure, where the necessary entanglement is created between nuclear and electronic spins of each individual atom. This state provides improvement in measurement sensitivity beyond the standard quantum limit for quantum memory experiments and applications in quantum metrology and is thus a complementary alternative to spin squeezing obtained via interatom entanglement. Squeezing of the collective spin is verified by quantum state tomography.

We show that by using laser catalysis, we can employ translationally cold ($T_r\approx 1.75\mathrm{K}$) collisions to produce ultracold ($0.01\mathrm{mK}<T_p<1\mathrm{mK}$) (homonuclear) molecules. We illustrate this approach by studying the laser catalysis of the ${}^6\mathrm{Li}+{}^6\mathrm{Li}{}^7\mathrm{Li}\stackrel{\hslash \omega }{\to }({}^6\mathrm{Li}{}^6\mathrm{Li}{}^7\mathrm{Li}{)}^{*}(1^4{A}^{\prime \prime })\stackrel{\hslash \omega }{\to }{}^6\mathrm{Li}{}^6\mathrm{Li}+{}^7\mathrm{Li}$ reaction in the collinear approximation. Ultracold ${}^6\mathrm{Li}{}^6\mathrm{Li}$ product molecules are shown to be produced at an extraordinary yield of up to 99.97%, using moderate laser intensities of $I=100\mathrm{kW}/{\mathrm{cm}}^2-10\mathrm{MW}/{\mathrm{cm}}^2$.

We apply a feedback cooling technique to simultaneously cool the three electromechanical normal modes of the ton-scale resonant-bar gravitational wave detector AURIGA. The measuring system is based on a dc superconducting quantum interference device (SQUID) amplifier, and the feedback cooling is applied electronically to the input circuit of the SQUID. Starting from a bath temperature of 4.2 K, we achieve a minimum temperature of 0.17 mK for the coolest normal mode. The same technique, implemented in a dedicated experiment at subkelvin bath temperature and with a quantum limited SQUID, could allow to approach the quantum ground state of a kilogram-scale mechanical resonator.

We demonstrate laser-field-free molecular orientation with the combination of a moderate electrostatic field and an intense nonresonant rapidly turned-off laser field, which can be shaped with the plasma shutter technique. We use OCS (carbonyl sulfide) molecules as a sample. Molecular orientation is adiabatically created in the rising part of the laser pulse, and it is found to revive at around the rotational period of an OCS molecule with the same degree of orientation as that at the peak of the laser pulse in the virtually laser-field-free condition. This accomplishment means that a new class of molecular sample has become available for various applications.

We predict squeezed light generation through the spontaneous rotational symmetry breaking occurring in a degenerate optical parametric oscillator (DOPO) pumped above threshold. We show, within the linearized theory, that a DOPO with spherical mirrors, in which the signal and idler fields correspond to first-order Laguerre-Gauss modes, produces a perfectly squeezed vacuum with the shape of a Hermite-Gauss mode. This occurs at any pumping level above threshold; hence, the phenomenon is noncritical. Imperfections of the rotational symmetry, due, e.g., to cavity anisotropy, are shown to have a small impact.

We report the stopping of an atomic beam, using a series of pulsed electromagnetic coils. We use a supersonic beam of metastable neon created in a gas discharge as a monochromatic source of paramagnetic atoms. A series of coils is fired in a timed sequence to bring the atoms to near rest, where they are detected on a microchannel plate. Applications to fundamental problems in physics and chemistry are discussed.

We report the cooling of an atomic ensemble with light, where each atom scatters only a single photon on average. This is a general method that does not require a cycling transition and can be applied to atoms or molecules that are magnetically trapped. We discuss the application of this new approach to the cooling of hydrogenic atoms for the purpose of precision spectroscopy and fundamental tests.

We demonstrate a quantum stroboscope based on a sequence of identical attosecond pulses that are used to release electrons into a strong infrared (IR) laser field exactly once per laser cycle. The resulting electron momentum distributions are recorded as a function of time delay between the IR laser and the attosecond pulse train using a velocity map imaging spectrometer. Because our train of attosecond pulses creates a train of identical electron wave packets, a single ionization event can be studied stroboscopically. This technique has enabled us to image the coherent electron scattering that takes place when the IR field is sufficiently strong to reverse the initial direction of the electron motion causing it to rescatter from its parent ion.

A novel approach for the generation of subwavelength structures in interferometric optical lithography is described. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. Since this process only comprises resonant atom-field interactions, a multiphoton absorption medium is not required. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at very low laser intensities.

We present a precise theoretical prediction for the decay width of the bound state of two electrons and a positron (a negative positronium ion), $\Gamma ({\mathrm{Ps}}^{-})=2.087963(12)/\mathrm{ns}$. We include $O({\alpha }^2)$ effects of hard virtual photons as well as soft corrections to the wave function and the decay amplitude. An outcome of a large-scale variational calculation, this is the first result for second-order corrections to a decay of a three-particle bound state. It will be tested experimentally in the new positronium-ion facility in Garching in Germany.

We present experiments where a single subwavelength scatterer is used to examine and control the backscattering induced coupling between counterpropagating high-$Q$ modes of a microsphere resonator. Our measurements reveal the standing wave character of the resulting symmetric and antisymmetric eigenmodes, their unbalanced intensity distributions, and the coherent nature of their coupling. We discuss our findings and the underlying classical physics in the framework common to quantum optics and provide a particularly intuitive explanation of the central processes.

We show that photon nonlinearities in an electromagnetically induced transparency can be at least 1 order of magnitude larger than predicted in all previous approaches. As an application we demonstrate that in this regime they give rise to very strong photon-photon interactions which are strong enough to make an experimental realization of a photonic Mott insulator state feasible in arrays of coupled ultrahigh-$Q$ microcavities.

We present a method of simulating the Dirac equation in $3+1$ dimensions for a free spin-$1/2$ particle in a single trapped ion. The Dirac bispinor is represented by four ionic internal states, and position and momentum of the Dirac particle are associated with the respective ionic variables. We show also how to simulate the simplified $1+1$ case, requiring the manipulation of only two internal levels and one motional degree of freedom. Moreover, we study relevant quantum-relativistic effects, like the Zitterbewegung and Klein’s paradox, the transition from massless to massive fermions, and the relativistic and nonrelativistic limits, via the tuning of controllable experimental parameters.

Electromagnetically induced transparency is predicted for x rays in laser-dressed neon gas. The x-ray photoabsorption cross section and polarizability near the Ne $K$ edge are calculated using an ab initio theory suitable for optical strong-field problems. The laser wavelength is tuned close to the transition between $1s^{-1}3s$ and $1s^{-1}3p$ ($\sim 800\mathrm{nm}$). The minimum laser intensity required to observe electromagnetically induced transparency is of the order of ${10}^{12}\mathrm{W}/{\mathrm{cm}}^2$. The ab initio results are discussed in terms of an exactly solvable three-level model. This work opens new opportunities for research with ultrafast x-ray sources.

We demonstrate experimentally a procedure to obtain the maximum efficiency for the storage and retrieval of light pulses in atomic media. The procedure uses time-reversal to obtain optimal input signal pulse shapes. Experimental results in warm Rb vapor are in good agreement with theoretical predictions and demonstrate a substantial improvement of efficiency. This optimization procedure is applicable to a wide range of systems.

We demonstrate the reversible mapping of a coherent state of light with a mean photon number $\overline{n}\simeq 1.1$ to and from the hyperfine states of an atom trapped within the mode of a high-finesse optical cavity. The coherence of the basic processes is verified by mapping the atomic state back onto a field state in a way that depends on the phase of the original coherent state. Our experiment represents an important step toward the realization of cavity QED-based quantum networks, wherein coherent transfer of quantum states enables the distribution of quantum information across the network.

We report enhancement of the spin polarization of ${}^{133}\mathrm{Cs}$ nuclei in CsH salt by spin transfer from an optically pumped cesium vapor. The nuclear polarization was 4.0 times the equilibrium polarization at 9.4 T and $137°\mathrm{C}$, with larger enhancements at lower fields. This work is the first demonstration of spin transfer from a polarized alkali vapor to the nuclei of a solid, opening up new possibilities for research in hyperpolarized materials.

Optical pumping by blackbody radiation is a feature shared by all polar molecules and fundamentally limits the time that these molecules can be kept in a single quantum state in a trap. To demonstrate and quantify this, we have monitored the optical pumping of electrostatically trapped OH and OD radicals by room-temperature blackbody radiation. Transfer of these molecules to rotationally excited states by blackbody radiation at 295 K limits the $1/e$ trapping time for OH and OD in the $X^2{\Pi }_{3/2}$, $v^{\prime \prime }=0$, $J^{\prime \prime }=3/2(f)$ state to 2.8 and 7.1 s, respectively.

We report the generation of a beam of slow (translationally cold) KBr molecules formed by exoergic reactive collisions in counterpropagating beams of K atoms and HBr molecules. The intensity of the slow beam is estimated to $4\times {10}^{11}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$. The velocity distribution (density) peaks at $42.5\mathrm{m}/\mathrm{s}$ corresponding to a formal temperature of 13 K. About 7% of the molecules move at velocities between 14.2 and $20\mathrm{m}/\mathrm{s}$ and an estimated fraction of 7% is slower than $14.2\mathrm{m}/\mathrm{s}$.