Click to increase image sizeClick to decrease image size Acknowledgments Reprinted from Laser Spectroscopy, Techniques and Applications, Marcel Dekker, Inc., New York, 1995, 5–43. In addition to the texts cited in the reference section, there are a number of classic texts that deal with atomic and molecular spectroscopy as well as group-theoretical considerations, and that might be useful to the reader. A few representative ones are:
We use ultracold spin--1/2 atomic fermions ($^6$Li) to realize the Hubbard model on a three-dimensional (3D) optical lattice. At relatively high temperatures and at densities near half-filling, we show that the gas forms a Mott insulator with unordered spins. To observe antiferromagnetic order that is predicted to occur at lower temperatures, we developed the compensated optical lattice method to evaporatively cool atoms in the lattice. This cooling has enabled the detection of short-range magnetic order by spin-sensitive Bragg scattering of light.
The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.
High-precision laser spectroscopy of atomic energy levels enables the measurement of nuclear properties. Sensitivity to these properties is particularly enhanced in muonic atoms which are bound systems of a muon and a nucleus. Exemplary is the measurement of the proton charge radius from muonic hydrogen performed by the CREMA collaboration which resulted in an order of magnitude more precise charge radius as extracted from other methods but at a variance of 7 standard deviations. Here, we summarize the role of muonic atoms for the extraction of nuclear charge radii, we present the status of the so called "proton charge radius puzzle", and we sketch how muonic atoms can be used to infer also the magnetic nuclear radii, demonstrating again an interesting interplay between atomic and particle/nuclear physics.
We report on the state of the art of quantum walk experiments with neutral atoms in state-dependent optical lattices. We demonstrate a novel state-dependent transport technique enabling the control of two spin-selective sublattices in a fully independent fashion. This transport technique allowed us to carry out a test of single-particle quantum interference based on the violation of the Leggett-Garg inequality and, more recently, to probe two-particle quantum interference effects with neutral atoms cooled into the motional ground state. These experiments lay the groundwork for the study of discrete-time quantum walks of strongly interacting, indistinguishable particles to demonstrate quantum cellular automata of neutral atoms.
We report on the current performance of our atom interferometry gravity gradiometer. After careful elimination of the main sources of fluctuations and biases in the atom interferometer, we achieve a sensitivity of 3×10-9 g per second to differential gravity; by modulating the position of a set of source masses, we achieve a relative statistical uncertainty of 1.1 × 10-4 to the gravitational constant G.
We demonstrate high resolution frequency comb spectroscopy in the extreme ultraviolet for the first time by exciting helium from the ground state using 51.56 nm pulses. Precision spectroscopy in the extreme ultraviolet on helium atoms and helium+ ions is very interesting as it could provide more stringent tests of quantum electrodynamics than currently possible with hydrogen. One problem is that spectroscopy in the extreme ultraviolet typically requires amplification and harmonic upconversion of visible light sources, which can introduce difficult to control systematic errors as a result of so called frequency -chirping effects.
Recently, there has been important progress in the formation of ultracold polar molecules in the rovibrational ground state, thus opening intriguing perspectives for the investigation of strongly correlated quantum systems under the influence of long-range dipolar forces. After an brief introduction into the field of ultracold molecules, we will review our recent experiments on the formation of ultracold LiCs molecules in the absolute ground state (XE+)-E-1, v=0, J=0 via a single photo-association step starting from laser-cooled atoms.
Entanglement, a key feature of quantum mechanics, is a resource that allows the improvement of precision measurements beyond the conventional bound attainable by classical means. This results in the standard quantum limit, which is reached in today's best available sensors of various quantities such as time and position. Many of these sensors are interferometers in which the standard quantum limit can be overcome by using quantum-entangled states (in particular spin squeezed states) at the two input ports. Bose-Einstein condensates of ultracold atoms are considered good candidates to provide such states involving a large number of particles. Here we demonstrate spin squeezed states suitable for atomic interferometry by splitting a condensate into a few parts using a lattice potential. Site-resolved detection of the atoms allows the measurement of the atom number difference and relative phase, which are conjugate variables. The observed fluctuations imply entanglement between the particles, a resource that would allow a precision gain of 3.8 dB over the standard quantum limit for interferometric measurements.
