Radio-frequency induced spin transitions of one individual proton are observed. The spin quantum jumps are detected via the continuous Stern-Gerlach effect, which is used in an experiment with a single proton stored in a cryogenic Penning trap. This is an important milestone towards a direct high-precision measurement of the magnetic moment of the proton and a new test of the matter-antimatter symmetry in the baryon sector.

We report the direct observation of optical precursors of heralded single photons with step- and square-modulated wave packets passing through cold atoms. Using electromagnetically induced transparency and the slow-light effect, we separate the single-photon precursor, which always travels at the speed of light in vacuum, from its delayed main wave packet. In the two-level superluminal medium, our result suggests that the causality holds for a single photon.

Three oriented bosonic dipoles are treated by using the hyperspherical adiabatic representation, providing numerical evidence that the Efimov effect persists near a two-dipole resonance and in a system where angular momentum is not conserved. Our results further show that the Efimov features in scattering observables become universal, with a known three-body parameter; i.e., the resonance energies depend only on the two-body physics, which also has implications for the universal spectrum of the four-dipole problem. Moreover, the Efimov states should be long-lived, which is favorable for their creation and manipulation in ultracold dipolar gases. Finally, deeply bound two-dipole states are shown to be relatively stable against collisions with a third dipole, owing to the emergence of a repulsive interaction originating in the angular momentum nonconservation for this system.

We have produced laser-cooled Wigner crystals of ${}^{229}\mathrm{Th}^{3+}$ in a linear Paul trap. The magnetic dipole ($A$) and electric quadrupole ($B$) hyperfine constants for four low-lying electronic levels and the relative isotope shifts with respect to ${}^{232}\mathrm{Th}^{3+}$ for three low-lying optical transitions are measured. Using the hyperfine $B$ constants in conjunction with prior atomic structure calculations, a new value of the spectroscopic nuclear electric quadrupole moment $Q=3.11(16)\mathrm{eb}$ is deduced. These results are a step towards optical excitation of the low-lying isomer level in the ${}^{229}\mathrm{Th}$ nucleus.

Atoms irradiated with combined femtosecond laser and extreme ultraviolet (XUV) fields ionize through multiphoton processes, even when the energy of the XUV photon is below the ionization potential. However, in the presence of two different XUV photons and an intense laser field, it is possible to induce full electromagnetic transparency. Taking helium as an example, the laser field modifies its electronic structure, while the presence of two different XUV photons and the laser field leads to two distinct ionization pathways that can interfere destructively. This work demonstrates a new approach for coherent control in a regime of highly excited states and strong optical fields.

The first experimental evidence of rotational Doppler broadening in photoelectron spectra, reported here, show good agreement with recently described theoretical predictions. The dependence of the broadening on temperature and photoelectron kinetic energy is quantitatively predicted by the theory. The experiments verify that the rotational contributions to the linewidth are comparable to those from translational Doppler broadening and must be considered in the analysis of high-resolution photoelectron spectra. A classical model accounting for this newly observed effect is presented.

We demonstrate the transverse confinement and guiding of a low energy electron beam of several electron volts in a miniaturized linear quadrupole guide. The guiding potential is generated by applying a microwave voltage to electrodes fabricated on a planar substrate, which allows the potential landscape to be precisely shaped on a microscopic scale. We realize transverse trapping frequencies of 100 MHz and guide electrons along a circular section of 37 mm length. A detailed characterization of the guiding properties in terms of potential depth and dynamic stability is given. This new technique of electron guiding promises various applications in guided matter-wave experiments such as electron interferometry.

We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of ${}^6\mathrm{Li}$ by ${}^{174}\mathrm{Yb}$ and extract the $s$-wave scattering length magnitude $|a_{{}^6\mathrm{Li}\mathrm{\text{−}}{}^{174}\mathrm{Yb}}|=(13\pm 3)a_0$ from the rate of interspecies thermalization. Using forced evaporative cooling of ${}^{174}\mathrm{Yb}$, we achieve reduction of the ${}^6\mathrm{Li}$ temperature to below the Fermi temperature, purely through interspecies sympathetic cooling.

In this work we show that light-matter excitations (polaritons) generated inside a hollow-core one-dimensional fiber filled with two types of atoms, can exhibit Luttinger liquid behavior. We first explain how to prepare and drive this quantum-optical system to a strongly interacting regime, described by a bosonic two-component Lieb-Liniger model. Utilizing the connection between strongly interacting bosonic and fermionic systems, we then show how spin-charge separation could be observed by probing the correlations in the polaritons. This is performed by first mapping the polaritons to propagating photon pulses and then measuring the effective photonic spin and charge densities and velocities by analyzing the correlations in the emitted photon spectrum. The necessary regime of interactions is achievable with current quantum-optical technology.

Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric ${}^{39}\mathrm{Ar}$ ($\mathrm{\text{half-life}}=269\mathrm{yr}$), a cosmogenic isotope with an isotopic abundance of $8\times {10}^{-16}$. In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

The nonlinear absorption mechanisms of neon atoms to intense, femtosecond kilovolt x rays are investigated. The production of ${\mathrm{Ne}}^{9+}$ is observed at x-ray frequencies below the ${\mathrm{Ne}}^{8+}$, $1s^2$ absorption edge and demonstrates a clear quadratic dependence on fluence. Theoretical analysis shows that the production is a combination of the two-photon ionization of ${\mathrm{Ne}}^{8+}$ ground state and a high-order sequential process involving single-photon production and ionization of transient excited states on a time scale faster than the Auger decay. We find that the nonlinear direct two-photon ionization cross section is orders of magnitude higher than expected from previous calculations.

We report experiments in which the line shape of the Lyman-alpha ($1S\mathrm{\text{−}}2P$) transition was measured for positronium (Ps) atoms both inside and outside a porous silica target. The energy interval $\Delta E$ for confined atoms was observed to be larger than that of free Ps by $1.26\pm 0.06\mathrm{meV}$. A configuration interaction calculation yields results that are consistent with our $\sim 5\mathrm{nm}$ sample, and suggests that $\Delta E$ decreases dramatically for larger cavity diameters. The linewidth of the transition, $(0.066\pm 0.004)\mathrm{nm}$ (FWHM), is about half of what one would expect for free Ps at room temperature due to the Dicke line narrowing effect of confinement. Such measurements can be used to determine void sizes in porous films and Ps dynamics therein, and elimination of the Doppler spread of atoms in a porous film could be useful for the efficient excitation of a Ps gas.

The detection of spatial and temporal electronic motion by scattering of subfemtosecond pulses of 10 keV electrons from coherent superpositions of electronic states of both H and $T_2^{+}$ is investigated. For the H atom, we predict changes in the diffraction images that reflect the time-dependent effective radius of the electronic charge density. For an aligned $T_2^{+}$ molecule, the diffraction image changes reflect the time-dependent localization or delocalization of the electronic charge density.

We report here the first successful synthesis of cold antihydrogen atoms employing a cusp trap, which consists of a superconducting anti-Helmholtz coil and a stack of multiple ring electrodes. This success opens a new path to make a stringent test of the CPT symmetry via high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atoms.

We propose a quantum optical method to do the subwavelength lithography. Our method is similar to the traditional lithography but adding a critical step before dissociating the chemical bound of the photoresist. The subwavelength pattern is achieved by inducing the multi-Rabi oscillation between the two atomic levels. The proposed method does not require multiphoton absorption and the entanglement of photons. It is expected to be realizable using current technology.

We demonstrate feedback cooling of the motion of a single rubidium atom trapped in a high-finesse optical resonator to a temperature of about $160\mu \mathrm{K}$. Time-dependent transmission and intensity-correlation measurements prove the reduction of the atomic position uncertainty. The feedback increases the $1/e$ storage time into the 1 s regime, 30 times longer than without feedback. Feedback cooling therefore rivals state-of-the-art laser cooling, but with the advantages that it requires less optical access and exhibits less optical pumping.

The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach.

We present a new method for the generation of rotationally and vibrationally state-selected, translationally cold molecular ions in ion traps. Our technique is based on the state-selective threshold photoionization of neutral molecules followed by sympathetic cooling of the resulting ions with laser-cooled calcium ions. Using ${\mathrm{N}}_2^{+}$ ions as a test system, we achieve $>90\%$ selectivity in the preparation of the ground rovibrational level and state lifetimes on the order of 15 minutes limited by collisions with background-gas molecules. The technique can be employed to produce a wide range of apolar and polar molecular ions in the ground and excited rovibrational states. Our approach opens up new perspectives for cold quantum-controlled ion-molecule-collision studies, frequency-metrology experiments with state-selected molecular ions and molecular-ion qubits.

Clusters of para-hydrogen ($p{\mathrm{H}}_2$) have been predicted to exhibit superfluid behavior, but direct observation of this phenomenon has been elusive. Combining experiments and theoretical simulations, we have determined the size evolution of the superfluid response of $p{\mathrm{H}}_2$ clusters doped with carbon dioxide (${\mathrm{CO}}_2$). Reduction of the effective inertia is observed when the dopant is surrounded by the $p{\mathrm{H}}_2$ solvent. This marks the onset of molecular superfluidity in $p{\mathrm{H}}_2$. The fractional occupation of solvation rings around ${\mathrm{CO}}_2$ correlates with enhanced superfluid response for certain cluster sizes.

We present an exact decomposition of the complete wave function for a system of nuclei and electrons evolving in a time-dependent external potential. We derive formally exact equations for the nuclear and electronic wave functions that lead to rigorous definitions of a time-dependent potential energy surface (TDPES) and a time-dependent geometric phase. For the ${\mathrm{H}}_2^{+}$ molecular ion exposed to a laser field, the TDPES proves to be a useful interpretive tool to identify different mechanisms of dissociation.