In classical mechanics the “vacuum” is empty (nothingness). In contrast, the vacuum of quantum mechanics is a volatile sea of ephemeral virtual particles. This Colloquium describes several processes in which these vacuum fluctuations are amplified into real observable particles, and how superconducting circuits can be used to realize such amplification mechanisms, and therefore explore the properties of the quantum vacuum.

How does rotation change the evolution, end stages, and stellar winds as well as types of supernovae explosions? This question is not only of importance for the fate of individual stars in galaxies, but also for the populations of blue and red supergiants, Wolf-Rayet stars, the progenitors of supernovae, and gamma ray bursts. The results influence the abundance evolution of chemical elements in galaxies. All aspects of stellar rotation are reviewed, including hydrodynamic instabilities, angular momentum transport, and radial mixing of matter. Predictions from models including rotations provide a better description of the observations as those without rotations.

Since the discovery of charm mesons in 1974 precision measurements of their decay in fixed target and colliding beam experiments at particle accelerators have yielded a wealth of information on the weak and strong interactions of heavy flavor quarks. This review summarizes what is presently known experimentally and theoretically in the field and provides an excellent foundation for future charm studies at the LHC and the next generation of $e^{+}{e}^{-}$ colliders.

The formation of domains in thin films of ferroelectrics, ferromagnets, ferroelastics, or multiferroics can be thought of as a consequence of a finite-size effect driven by a minimization of a surface energy. This review, which focuses on ferroelectrics, describes the energetics of domain formation and how domain walls can act as mobile interfaces suited to a variety of nanoelectronic devices. High-resolution studies at the atomic scale reveal functional properties within domain walls of magnetoelectric materials and broadens the discussion to include comparisons to magnetic materials and multiferroics.

As the mass and complexity of objects, such as molecules and atoms, increase, they behave more classically than quantum mechanically. Certain small systems such as clusters and molecules are on the border line between the classical and quantum description. In this Colloquium, the developments in the interferometry of these systems are described as well as the new physics that they bring to light.

Cold atomic gases have numerous applications, ranging from matter-wave interferometry to many-body physics. Atoms from the noble gas family play a special role in this research. Indeed each atom must be prepared in a metastable electronic state in order to be manipulated by laser light, and it thus carries a large internal energy. This article surveys the specific properties of these metastable noble gases, such as their unique collision dynamics. The relevance of these gases for metrology is also discussed.

The top quark is the highest-mass fundamental constituent of matter observed so far. Because of this large mass, top quark interactions might receive sizable contributions from new heavy particles that impact its production and decays. Evidence for such effects can be observed as deviations from standard model expectations or as the production of exotic new particles, among them the Higgs particle. Over the past fifteen years of experimentation at the Tevatron, detailed studies have been performed and analysis techniques have been developed that have resulted in precision mass and cross section measurements and have led to more stringent limits on new phenomena. Many of these results and techniques, including a few puzzling signatures, are becoming the basis for research at higher energies at the Large Hadron Collider at CERN.

The complex oxide perovskite ${\mathrm{SrRuO}}_3$ is recognized as an almost ideal material for study: it can be grown epitaxially on a variety of complex oxide substrates, it is a good conductor without the need for added dopants, and it is a model system for the study of itinerant ferromagnetism with intermediate strength electron correlations. This review discusses the preparation, characterization, and applications of ${\mathrm{SrRuO}}_3$ thin films and addresses still incompletely understood properties, namely, bad metal behavior at high temperatures that evolves at low temperatures to Fermi liquid behavior accompanied by a paramagnetic-to-ferromagnetic transition having a high magnetocrystalline anisotropy.

Strongly correlated fermion systems provide large challenges to theoretical treatments. A particular tool, the functional renormalization group that goes back to Wilson, but has been much refined and further developed in recent years, has been successfully applied to problems ranging from quantum phase transitions to quantum dots and wires. In this review a pedagogical introduction to this important technique and its applications is provided.

To understand the origin of the elements heavier than iron, innovative nuclear-fuel cycles, and nuclear weapon test data, a detailed knowledge of certain reaction cross section is required. Oftentimes, when the key reactions cannot be studied directly or predicted reliably, it becomes necessary to develop indirect, or surrogate, techniques. This review discusses the foundations and applications of the surrogate nuclear reaction approach, and the prospects for the future, especially at rare-isotope facilities.

This review article surveys the theoretical structure, experimental status, and physics implications of the large variety of neutral and charged kaon decay modes. These have been important for establishing the fundamental structure of the electroweak interactions, determining elements of the Cabibbo-Kobayashi-Maskawa mixing matrix, discovering and studying $CP$ violation, probing the flavor symmetries of the strong interactions at low energy and developing chiral perturbation theory, and searching for new physics effects in rare decay modes.